$300,000,000

Ciena Corporation

       0.25% Convertible Senior Notes due 2013

       The notes will bear interest at a rate of 0.25% per annum. We will pay interest on the notes on May 1 and November 1 of each year, beginning November 1, 2006. The notes will mature on May 1, 2013.

       Notes may be converted prior to maturity (unless earlier repurchased or redeemed) at the option of the holder into shares of our common stock at the initial conversion rate of 177.1009 shares of our common stock per $1,000 in principal amount of notes, which is equal to an initial conversion price of approximately $5.65 per share.

       Shares of our common stock are traded on the Nasdaq National Stock Market under the symbol “CIEN.” The closing sale price of our common stock on April 4, 2006 was $4.91 per share.

       The notes are not redeemable prior to May 5, 2009. At any time on or after May 5, 2009, if the closing sale price of our common stock for at least 20 trading days in the 30 consecutive trading day period ending on the date one day prior to the date of a notice of redemption is greater than 130% of the applicable conversion price on the date of such notice, we may redeem the notes in whole or in part at a cash redemption price equal to 100% of the principal amount of the notes to be redeemed plus accrued and unpaid interest, if any, to the date of redemption.

       You may require us to repurchase, for cash, all or a portion of your notes upon the occurrence of a fundamental change (as defined in this prospectus supplement) at a purchase price equal to 100% of their principal amount, plus accrued and unpaid interest, if any, to the repurchase date or, in certain cases, to convert your notes at an increased conversion rate based on the price paid per share of our common stock in a transaction constituting a fundamental change.

       The notes will be our senior unsecured obligations and will rank pari passu with all of our other senior unsecured debt and senior to all of our future subordinated debt. The notes will be structurally subordinated to all present and future debt and other obligations of our subsidiaries. In addition, the notes are effectively subordinated to all of our present and future secured debt to the extent of the value of the collateral securing such debt.

       We do not intend to apply for a listing of the notes on any national securities exchange or for inclusion of the notes on any automatic quotation system.

       See “Risk Factors” beginning on page S-5 of this prospectus supplement to read about important factors you should consider before buying the notes.

       Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

       The public offering price set forth above does not include accrued interest, if any. Interest on the notes will accrue from the date of original issuance, expected to be April 10, 2006.

       To the extent Goldman, Sachs & Co. sells more than $300,000,000 in principal amount of notes, Goldman, Sachs & Co. will have the option to purchase up to an additional $45,000,000 in principal amount of notes from us at the offering price less the underwriting discount.

       Goldman, Sachs & Co. expects to deliver the notes through The Depository Trust Company against payment in New York, New York on April 10, 2006.

Goldman, Sachs & Co.

Prospectus Supplement dated April 4, 2006 to Prospectus dated April 3, 2006.

CALCULATION OF REGISTRATION FEE

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

       You should rely only on the information provided or incorporated by reference in this prospectus supplement, the accompanying prospectus and any “free writing prospectus” we may authorize to be delivered to you. We have not authorized anyone to provide you with different or additional information. We are not making an offer to sell the notes in any jurisdiction where the offer or sale of the notes is not permitted. You should not assume that the information appearing in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference is accurate as of any date other than their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

       When used in this prospectus supplement, except where the context otherwise requires, the terms “we,” “us” and “our” refer to Ciena Corporation.

       We have a 52 or 53 week fiscal year, which ends on the Saturday nearest to the last day of October in each year. For purposes of financial statement presentation, each fiscal year is described as having ended on October 31. Fiscal 2002, fiscal 2003, fiscal 2004 and fiscal 2005 comprised 52 weeks and fiscal 2001 comprised 53 weeks.

RISK FACTORS

       Your investment in the notes involves certain risks. Before deciding to invest, you should consider carefully, among other matters, the following discussion of risks and the other information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus.

Risk Factors Related to Our Business

       If any of these risks are realized our business, prospects, financial condition, results of operations and our ability to service debt could be materially adversely affected.

We face intense competition that could hurt our sales and our ability to achieve and maintain profitability.

       The markets in which we compete for sales of networking equipment, software and services are extremely competitive, particularly the market for sales to telecommunications service providers. Competition in these markets is based on any one or a combination of the following factors: price, functionality, manufacturing capability, installation, services, existing business and customer relationships, scalability and the ability of products and services to meet customers’ immediate and future network requirements. A small number of very large companies have historically dominated the communications networking equipment industry. Our industry has also increasingly experienced competition from low-cost producers in Asia. Many of our competitors have substantially greater financial, technical and marketing resources, greater manufacturing capacity and better established relationships with incumbent carriers and other potential customers than us. As a result of increased merger activity among communication service providers, there has been speculation of consolidation among networking equipment providers, which, if it occurred, could cause some competitors to grow even larger and more powerful. On April 2, 2006, Alcatel and Lucent, two large competitors, announced a definitive agreement to merge, and the effect of this merger on us, should it occur, may be adverse to our competitive position.

       We also compete with a number of smaller companies that provide significant competition for a specific product or market. These competitors often base their products on the latest available technologies. Due to the narrower focus of their efforts, these competitors may achieve commercial availability of their products more quickly and may be more attractive to customers. As we seek to expand our channel sales strategy, we also may face competition from resellers and distributors of some of our products, who may be competitors in other customer markets or with respect to complementary technologies.

       Increased competition in our markets has resulted in aggressive business tactics, including:

       The tactics described above can be particularly effective in an increasingly concentrated base of potential customers such as communications service providers. Our inability to compete successfully in our markets would harm our sales and our ability to achieve and maintain profitability.

       Our revenue can fluctuate unpredictably from quarter to quarter. Fluctuations in our revenue can lead to even greater fluctuations in our operating results. Our budgeted expense levels depend in part on our expectations of future revenue. Any substantial adjustment to expenses to account for lower levels of revenue is difficult and takes time. Consequently, if our revenue declines, our levels of inventory, operating expense and general overhead would be high relative to revenue, resulting in additional operating losses.

       Other factors contribute to fluctuations in our revenue and operating results, including:

       Many of these factors are beyond our control, particularly in the case of large carrier orders and multi-vendor or multi-technology network builds where the achievement of certain performance thresholds for acceptance is subject to the readiness and performance of the customer or other providers and changes in customer requirements or installation plans. Any one or a combination of the factors above may cause our revenue and operating results to fluctuate from quarter to quarter. These fluctuations may make it difficult to manage our business and achieve or maintain profitability. As a consequence, our revenues and operating results for a particular quarter may be difficult to predict and our prior results are not necessarily indicative of results likely in future periods.

Our gross margin may fluctuate from quarter to quarter and our product gross margins may be adversely affected by a number of factors, some of which are beyond our control.

       Our gross margin fluctuates from period to period and our product gross margin may be adversely affected by numerous factors, including:

Our business and results of operations are significantly affected by conditions in the communications industry, including increases in consolidation activity.

       The last few years have seen substantial changes in the communications industry. Many of our customers and potential customers, including telecommunications service providers that have historically provided a significant portion of our sales, have confronted static or declining revenue for their traditional voice services. Traditional communications service providers are under increasing competitive pressure from providers within their industry and other participants that offer, or seek to offer, overlapping or similar services. These pressures are likely to continue to cause communications service providers to seek to minimize the costs of the equipment that they buy and may cause static or reduced capital expenditures by customers or potential customers. These competitive pressures may also result in pricing becoming a more important factor in customer purchasing decisions. Increased focus on pricing may favor low-cost vendors in Asia and larger competitors that can spread the effect of price discounts across a broader offering of products and services and across a larger customer base.

       Several large communications service providers have recently completed merger transactions. These included the mergers of Verizon and MCI, and SBC and AT&T, all of which have been significant customers during prior periods. In addition, AT&T has also announced its plans to acquire BellSouth, which has also been a significant customer during prior periods. These mergers will have a major impact on the future of the telecommunications industry. They will further increase concentration of purchasing power among a few large service providers and may result in delays in, or the curtailment of, investments in communications networks, as a result of changes in strategy, network overlap, cost reduction efforts or other considerations. These industry conditions may negatively affect our business, financial condition and results of operation.

We may not be successful in selling our products into new markets and developing and managing new sales channels.

       We continue to take steps to sell our expanded product portfolio into new markets and to a broader customer base, including communication service providers, enterprises, cable operators, and federal, state and local governments. To succeed in these markets, we believe we must develop and manage new sales channels and distribution arrangements. We expect these relationships to be an increasing part of our business as we seek to grow. Because we have only limited experience in developing and managing such channels, we may not be successful in reaching additional customer segments, expanding into new geographic regions, or reducing the financial risks of entering new markets and pursuing new customer segments. In addition, sales to federal, state and local governments require compliance with complex procurement regulations with which we have little experience. We may be unable to increase our sales to government contractors if we determine that we cannot comply with applicable regulations. Our failure to comply with regulations for existing contracts could result in civil, criminal or administrative proceedings involving fines and suspension or debarment from federal government contracts. Failure to manage additional sales channels effectively would limit our ability to succeed in these new markets and could adversely affect our ability to grow our customer base and revenues.

       In recent years we have sought to add large, incumbent communication service providers as customers for our products, software and services. Our future success will depend on our ability to maintain and expand our sales to these existing communications service provider customers and add new customers. Many of our competitors have long-standing relationships with communications service providers, which can pose significant obstacles to our sales efforts. Sales to large communications service providers typically involve lengthy sales cycles, protracted or difficult contract negotiations, and extensive product testing and network certification. We are sometimes required to assume terms or conditions that negatively affect pricing, payment and the timing of revenue recognition in order to consummate a sale. This may negatively affect the timing of revenue recognition, which would, in turn, negatively affect our gross margin and results of operations. Communications service providers may ultimately insist upon terms and conditions, that we deem too onerous or not in our best interest. As a result, we may incur substantial expenses and devote time and resources to potential relationships that never materialize.

Continued shortages in component supply or manufacturing capacity could increase our costs, adversely affect our results of operations and constrain our ability to grow our business.

       As we have expanded our product portfolio, increased our use of contract manufacturers and increased our product sales in recent years, manufacturing capacity and supply constraints related to components and subsystems have become increasingly significant issues for us. We have encountered and continue to experience component shortages that have affected our operations and ability to deliver products timely to customers. Growth in customer demand for the communications networking products supplied by us, our competitors and other third parties, has resulted in supply constraints among providers of some components used in our products. Component shortages and manufacturing capacity constraints may also arise, or be exacerbated by difficulties with our suppliers or contract manufacturers, or our failure to adequately forecast our component or manufacturing needs. If shortages or delays persist or worsen, the price of required components may increase, or the components may not be available at all. If we are unable to secure the components or subsystems that we require at reasonable prices, or are unable to secure manufacturing capacity adequate to meet our needs, we may not be able to satisfy our contractual obligations to customers and our revenue and gross margin could be materially affected. We may also be subject to payment of liquidated damages for delays under customer contracts, and our customer relationships and business reputation may be harmed.

Product performance problems could damage our business reputation and limit our sales prospects.

       The development and production of new products with high technology content is complicated and often involves problems with software, components and manufacturing methods. Modifying our products to enable customers to integrate them into a new type of network architecture entails similar risks. If significant reliability, quality, or network monitoring problems develop as a result of our product development, manufacturing or integration, a number of negative effects on our business could result, including:

       Because we outsource manufacturing and use a direct order fulfillment model for certain of our products, we may be subject to product performance problems resulting from the acts or omissions of these third parties. These product performance problems could damage our business reputation and negatively affect our sales.

We must continue to make substantial and prudent investments in product development in order to keep pace with technological advances and succeed in existing and new markets for our products.

       In order to be successful, we must balance our initiatives to reduce our operating costs against the need to keep pace with technological advances. The market for communications networking equipment, software and services is characterized by rapid technological change, frequent introductions of new products, and recurring changes in customer requirements. To succeed, we must continue to develop new products and new features for existing products that meet customer requirements and market demand. In addition, we must be able to identify and gain access, including any applicable third party licenses, to new technologies as our market segments evolve. Because our market segments are constantly evolving, we may allocate development resources toward products or technologies for which market demand is lower than anticipated. We may ultimately decide that such lower than expected demand no longer warrants continued investment in a product or technology. These decisions are difficult and may be disruptive to our business and our relationship with customers. Managing our efforts to keep pace with new technologies and reduce operating expense is difficult and there is no assurance that we will be successful.

We may be required to take further write-downs of goodwill and other intangible assets.

       As of January 31, 2006, we had $232.0 million of goodwill on our balance sheet. This amount primarily represents the remaining excess of the total purchase price of our acquisitions over the fair value of the net assets acquired. At January 31, 2006, we had $113.1 million of other intangible assets on our balance sheet. The amount primarily reflects purchased technology from our acquisitions. At January 31, 2006, goodwill and other intangible assets represented approximately 22.3% of our total assets. During the fourth quarter of 2005, we incurred a goodwill impairment charge of approximately $176.6 million and an impairment of other intangibles of $45.7 million. If we are required to record additional impairment charges related to goodwill and other intangible assets, such charges would have the effect of decreasing our earnings or increasing our losses in such period. If we are required to take a substantial impairment charge, our earnings per share or net loss per share could be materially adversely affected in such period.

We may experience unanticipated delays in the development and enhancement of our products that may negatively affect our competitive position and business.

       Because our products are based on complex technology, we can experience unanticipated delays in developing, improving, manufacturing or deploying them. Each step in the development life cycle of our products presents serious risks of failure, rework or delay, any one of which could decrease the timing and cost effective development of such product and could affect customer acceptance of the product. Specialized application specific integrated circuits (“ASICs”) and intensive software testing and validation are key to the timely introduction of enhancements to several of our products, and schedule delays are common in the final validation phase, as well as in the manufacture of specialized ASICs. In addition, unexpected intellectual property disputes, failure of critical design elements, and a host of other execution risks may delay or even prevent the introduction of these products. If we do not develop and successfully introduce products in a timely

We may incur significant costs and our competitive position may suffer as a result of our efforts to protect and enforce our intellectual property rights or respond to claims of infringement from others.

       Despite efforts to protect our proprietary rights, unauthorized parties may attempt to copy or otherwise obtain and use our products or technology. This is likely to become an increasingly important issue as we expand our operations and product development into countries that provide a lower level of intellectual property protection. Monitoring unauthorized use of our products is difficult, and we cannot be certain that the steps that we are taking will prevent unauthorized use of our technology. If competitors are able to use our technology, our ability to compete effectively could be harmed.

       In recent years, we have filed suit to enforce our intellectual property rights and, from time to time, have been subject to litigation and other third party intellectual property claims, including as a result of our indemnification obligations to customers or resellers that purchase our products. The frequency of these assertions is increasing as patent holders, including entities that are not in our industry and that purchase patents as an investment or to monetize such rights by obtaining royalties, use infringement assertions as a competitive tactic and a source of additional revenue. Intellectual property claims can significantly divert the time and attention of our personnel and result in costly litigation. Our pending patent infringement litigation with Nortel Networks, described in our Form 10-Q for the fiscal quarter ended January 31, 2006, which is incorporated by reference into the registration statement of which this prospectus is a part, has resulted in, and is likely to continue to result in, significant costs. If we are unsuccessful in this litigation, we may be required to pay significant damages, and could be enjoined from marketing or selling certain products. Intellectual property infringement claims can also require us to pay substantial royalties, enter into license agreements and/or develop non-infringing technology. Accordingly, the costs associated with third party intellectual property claims could adversely affect our business, results of operations and financial condition.

We may be required to write off significant amounts of inventory.

       In recent years, we have placed the majority of our orders to manufacture components or complete assemblies for many of our products only when we have firm orders from our customers. Because this practice can result in delays in the delivery of products to customers, we are increasingly ordering equipment and components from our suppliers based on forecasts of customer demand across all of our products. We believe this change is necessary in response to increased customer insistence upon shortened delivery terms. This change in our inventory purchases exposes us to the risk that our customers will not order those products for which we have forecasted sales, or will purchase fewer than the number of products we have forecasted. In such event, we may be required to write off, or write down inventory, potentially resulting in an accounting charge that could materially affect our results of operations for the quarter in which such charge occurs.

We must manage our relationships with electronic manufacturing service (EMS) providers in order to ensure that our product requirements are met timely and effectively.

       We rely on EMS providers to perform the majority of the manufacturing operations for our products and components, and are increasingly utilizing overseas suppliers, particularly in Asia. Because EMS providers are subject to many of the same risks as equipment vendors serving the communications industry, many EMS providers have experienced their own financial difficulties in recent years. The qualification of our EMS providers is a costly and time-consuming process, and these manufacturers build product for other companies, including our competitors. We are constantly reviewing our manufacturing capability, including the work of our EMS providers, to ensure that our

We depend on a limited number of suppliers, and for some items we do not have a substitute supplier.

       We depend on a limited number of suppliers for our product components and subsystems, as well as for equipment used to manufacture and test our products. Our products include several components for which reliable, high-volume suppliers are particularly limited. Some key optical and electronic components we use in our products are currently available only from sole or limited sources, and in some cases, that source also is a competitor. The loss of a source of key components could require us to re-engineer products that use those components, which would increase our costs. Increases in demand for components by us, our competitors or other third parties from sole or limited sources would result in additional supply constraints. Delays in component availability or delivery, or component performance problems, could result in delayed deployment of our products, and inability to recognize revenue, which would negatively affect our results of operations. These delays could also limit our opportunity to pursue additional growth or revenue opportunities and harm our business reputation and customer relationships.

Our international operations could expose us to additional risk and result in increased operating expense.

       We market, sell and service our products globally. We have established offices around the world, including in North America, Europe, Latin America and the Asia Pacific region. We have also established a development operation in India to pursue offshore development resources. In addition, we are increasingly relying upon overseas suppliers, particularly in Asia, to manufacture our products and components. We expect that our international activities will be dynamic over the foreseeable future as we enter some new markets and withdraw from or reduce operations in others in order to match our resources with revenue opportunities. These changes to our international operations will require significant management attention and financial resources. In some countries, our success will depend in part on our ability to form relationships with local partners. Our inability to identify appropriate partners or reach mutually satisfactory arrangements for international sales of our products could impact our ability to maintain or increase international market demand for our products.

       International operations are subject to inherent risks, and our future results could be adversely affected by a number of factors, including:

Our efforts to offshore certain resources and operations to India may not be successful and may expose us to unanticipated costs or liabilities.

       We have established a development operation in India and expect to increase hiring of personnel for this facility during the remainder of fiscal 2006. We have limited experience in offshoring our business functions, particularly development operations, and there is no assurance that our plan will enable us to achieve meaningful cost reductions or greater resource efficiency. Further, offshoring to India involves significant risks, including:

       Difficulties resulting from the factors above and other risks associated with offshoring could impair our development efforts, harm our competitive position and damage our reputation with existing and potential customers. These factors could be disruptive to our business and may cause us to incur substantial unanticipated costs or expose us to unforeseen liabilities.

The steps that we are taking to restructure our operations and align our resources with market opportunities could disrupt our business.

       We have taken several steps, including reductions in force, dispositions of assets and office closures, and internal reorganizations to reduce the size and cost of our operations and to better match our resources with our market opportunities. We expect to take additional steps to reduce our operating expenses. These efforts could be disruptive to our business. Reductions to headcount and other cost cutting measures may result in the loss of technical expertise that could adversely affect our research and development efforts and ability to meet product development schedules. Efforts to reduce operating expense often result in the recording of accounting charges, such as inventory and technology-related write-offs, workforce reduction costs, charges relating to consolidation of excess facilities, or claims from users of discontinued products. If we are required to take a substantial charge, our earnings per share or net loss per share would be adversely affected in such period. If we cannot manage our cost reduction and restructuring efforts effectively, our business, results of operations and financial condition could be harmed.

Our exposure to the credit risks of our customers and resellers may make it difficult to collect receivables and could adversely affect our operating results and financial condition.

       Industry and economic conditions have weakened the financial position of some of our customers. To sell to some of these customers, we may be required to take risks of uncollectible accounts. We may be exposed to similar risks relating to third party resellers and other sales channel partners, as we intend to increasingly utilize such parties as we enter into new geographic regions, particularly in Europe. While we monitor these situations carefully and attempt to take appropriate measures to protect ourselves, it is possible that we may have to write down or write off

If we are unable to attract and retain qualified personnel, we may be unable to manage our business effectively.

       If we are unable to retain and motivate our existing employees and attract qualified personnel to fill key positions, we may be unable to manage our business effectively, including the development of existing and new products. If we lose members of our management team or other key personnel, it may be difficult to replace them. Competition for highly skilled technical and other personnel with experience in our industry can be intense. Because we generally do not have employment contracts with our employees, we must rely upon providing competitive compensation packages and a high-quality work environment in order to retain and motivate employees. We have paid our employees significantly reduced or no bonuses for several years. In addition, we have informed employees that we will not be issuing stock options at the same level as historical grants. In addition to these compensation issues, we must continue to motivate and retain employees, which may be difficult due to morale challenges posed by our continuing workforce reductions and offshoring of certain operations.

Our failure to identify additional service delivery partners and manage our relationships with these partners effectively could adversely impact our financial results and relationship with customers.

       We rely on a number of service delivery partners, both domestic and international, to complement our global service and support resources. We expect to increasingly rely upon third party service delivery partners for the installation of our equipment in larger network builds, which often include more onerous installation, testing and acceptance terms. In order to ensure that we timely install our products and satisfy obligations to our customers, we must identify, train and certify additional appropriate partners. The certification of these partners can be costly and time-consuming, and these partners service products for other companies, including our competitors. There can be no assurance that we will be able to identify an adequate number of qualified service delivery partners. We may not be able to effectively manage our relationships with our partners and we cannot be certain that they will be able to deliver our services in the manner or time required. If our service partners are unsuccessful in delivering services:

We may be required to assume warranty, service and other unexpected obligations in connection with our resale of complementary products of other companies.

       We have entered into agreements with strategic partners that permit us to distribute the products of other companies. As part of our strategy to diversify our product portfolio and customer base, we may enter into additional resale agreements in the future. To the extent we succeed in reselling the products of these companies, we may be required by customers to assume certain warranty and service obligations. While our suppliers often agree to support us with respect to these obligations, we may be required to extend greater protection in order to effect a sale. Moreover, our suppliers are relatively small companies with limited financial resources. If they are unable to provide the required support, we may have to expend our own resources to do so. This risk is amplified because the equipment that we are selling has been designed and manufactured by other third parties and may be subject to warranty claims, the magnitude of which we are unable to evaluate

Our strategy of pursuing strategic acquisitions and investments may expose us to increased costs and unexpected liabilities.

       Our business strategy includes acquiring or making strategic investments in other companies to increase our portfolio of products and services, expand the markets we address, diversify our customer base and acquire or accelerate the development of new or improved products. To do so, we may use cash, issue equity that would dilute our current shareholders’ ownership, incur debt or assume indebtedness. Strategic investments and acquisitions involve numerous risks, including:

       As a result of these and other risks, any acquisitions or strategic investments may not reap the intended benefits and may ultimately have a negative impact on our business, results of operation and financial condition.

We may be adversely affected by fluctuations in currency exchange rates.

       Historically, our primary exposure to currency exchange rates has been related to non-U.S. dollar denominated operating expenses in Europe, Asia and Canada where we sell primarily in U.S. dollars. As we increase our international sales and utilization of international suppliers, we expect to transact additional business in currencies other than the U.S. dollar. As a result, we will be subject to the possibility of greater effects of foreign exchange translation on our financial statements. For those countries outside the United States where we have significant sales, a devaluation in the local currency would result in reduced revenue and operating profit and reduce the value of our local inventory presented in our financial statements. In addition, fluctuations in foreign currency exchange rates may make our products more expensive for customers to purchase or increase our operating costs, thereby adversely affecting our competitiveness. To date, we have not significantly hedged against foreign currency fluctuations; however, we may pursue hedging alternatives in the future. Although exposure to currency fluctuations to date has not had an adverse effect on our business, there can be no assurance that exchange rate fluctuations in the future will not have a material adverse effect on our revenue from international sales and, consequently, our business, operating results and financial condition.

Failure to maintain effective internal controls over financial reporting could have a material adverse effect on our business, operating results and stock price.

       Section 404 of the Sarbanes-Oxley Act of 2002 requires that we include in our annual report on Form 10-K, a report containing management’s assessment of the effectiveness of our internal

       We initially became subject to these requirements for our fiscal year ended October 31, 2005. Compliance with these requirements has resulted in, and is likely to continue to result in, significant costs, the commitment of time and operational resources and the diversion of management’s attention. Growth of our business, including our broader product portfolio and increased transaction volume, will necessitate ongoing changes to our internal control systems, processes and infrastructure, including our information systems. Our increasingly global operations, including our development facility in India and offices abroad, will pose additional challenges to our internal control systems as their operations become more significant. We cannot be certain that our current design for internal control over financial reporting, and any modifications necessary to reflect changes in our business, will be sufficient to enable management or our independent registered public accounting firm to determine that our internal controls are effective as of the end of fiscal 2006 or on an ongoing basis. If we are unable to assert that our internal controls over financial reporting are effective (or if our independent registered public accounting firm is unable to attest that our management’s report is fairly stated or they are unable to express an opinion on our management’s assessment of the effectiveness of internal controls over financial reporting or on the effectiveness of our internal controls over financial reporting), our business may be harmed. Market perception of our financial condition and the trading price of our stock may be adversely affected and customer perception of our business may suffer.

Our stock price is volatile.

       Our common stock price has experienced substantial volatility in the past, and may remain volatile in the future. Volatility can arise as a result of a number of the factors discussed in this “Risk Factors” section, as well as divergence between our actual or anticipated financial results and published expectations of analysts, and announcements that we, our competitors, or our customers may make.

Risks Related to an Investment in the Notes

Hedging transactions and other transactions may affect the value of the notes.

       Concurrently with the closing of the offering of the notes, we intend to use a portion of the net proceeds to purchase a call spread option relating to shares of our common stock from Goldman Sachs Financial Markets, L.P. (“GSFM”), an affiliate of Goldman, Sachs & Co. The call spread option is expected to reduce the potential dilution from conversion of the notes by effectively increasing the conversion price to us. The call spread option may subject us to certain risks and may not achieve the desired effect.

       The mitigating effect of the call spread option on dilution will be capped, which means that the call spread option may not completely mitigate dilution from conversion of the notes as intended. For example, if all notes were converted on the expiration date of the call spread option, the exercise of the call spread option would not mitigate dilution to the extent the market price per share of our common stock at the time of conversion exceeded the higher strike price of the call spread option. See “Call Spread Option” below.

       GSFM and its affiliates expect to engage in hedging transactions with respect to the call spread option. These hedging transactions involve entering into various derivative transactions such as swaps, with the initial hedging activity involving derivatives structured to achieve a similar position as would result from purchases of shares. Such hedging arrangements could increase the price of our common stock. These hedging transactions may occur in advance of and around the time of the

       GSFM, or any transferee of any of its positions, is likely to modify its hedge positions from time to time during the term of the call spread option by purchasing or selling shares of our common stock, our other securities or other instruments it may wish to use in connection with such hedging. The effect, if any, of these transactions and activities on the market price of our common stock or the notes will depend in part on market conditions and the settlement methods under the call spread option and cannot be ascertained at this time, but any of these activities may adversely affect the value of the notes and our common stock, and as a result, the value of the common stock you will receive upon the conversion of the notes.

       In connection with the call spread option described above, entities affiliated with GSFM may borrow shares in the stock loan market in advance of and around the time of the offering of the notes and may continue to borrow shares throughout the terms of the notes and the call spread option. These transactions may affect the liquidity and price to borrow shares in the stock loan market. We cannot assure you that such activity will not adversely affect the market price of our common stock and other equity-linked securities. In addition, the existence of the notes may encourage short selling in our common stock by market participants, which could depress the price of our common stock and other equity-linked securities.

Significant leverage and debt service obligations may adversely affect our cash flow and our ability to repay or repurchase the notes.

       We will have significant amounts of outstanding indebtedness, primarily related to the notes and our outstanding 3.75% Convertible Notes due February 1, 2008, upon the completion of this offering.

       As a result of this indebtedness, our principal and interest payment obligations will increase substantially. We may be unable to generate sufficient cash to pay the principal of, interest on and other amounts due in respect of our indebtedness, including the notes, when due. We may also add equipment loans and lease lines to finance capital expenditures and may obtain additional long-term debt, working capital lines of credit and lease lines.

       Our significant leverage could have important negative consequences, including:

       In addition, the notes will be our obligation exclusively. The indenture for the notes does not limit our ability, or that of our subsidiaries, to incur other indebtedness and liabilities. We may have difficulty paying what we owe under the notes if we or our subsidiaries incur additional indebtedness or other liabilities.

       Prior to the sale of the notes in this offering, there has been no public market for any of the notes, and there can be no assurance as to:

       If such a market were to exist, the notes could trade at prices that may be higher or lower than the principal amount or purchase price of the notes, depending on many factors, including prevailing interest rates, the market for similar notes, and our financial performance. We do not presently intend to apply for the listing of the notes on any securities exchange or for inclusion of the notes on any automated quotation system.

       The underwriters have advised us that they presently intend to make a market in the notes. The underwriters are not obligated, however, to make a market in the notes, and any such market-making may be discontinued at any time at the sole discretion of the underwriters. In addition, such market-making activity will be subject to the limits imposed by the Securities Act of 1933 and the Securities Exchange Act of 1934. Accordingly, no assurance can be given as to the development or liquidity of any market for the notes.

Holders of the notes may have to pay tax with respect to distributions on our common stock that they do not receive.

       The terms of the notes allow for changes in the conversion price of the notes in certain circumstances. A change in conversion price that allows holders of notes to receive more shares of common stock on conversion may increase those note holders’ proportionate interests in our earnings and profits or assets. In that case, U.S. holders (as defined under “Important United States Federal Income Tax Consequences”) could be treated as though they received a dividend in the form of our common stock under United States tax laws. Such a constructive stock dividend could be taxable to those note holders, although they would not actually receive any cash or other property. You should carefully consider the information under “Important United States Federal Income Tax Consequences.”

USE OF PROCEEDS

       We estimate that the net proceeds from this offering, after deducting estimated fees and expenses and underwriting discounts and commissions, will be approximately $292,200,000 ($336,075,000 if the underwriter exercises its option to purchase additional notes in full). We expect to use the net proceeds to provide additional funds for general corporate purposes. These purposes may include repurchases of our outstanding 3.75% Convertible Notes due February 1, 2008. These repurchases may occur at various prices from time to time.

       We also intend to use approximately $28,500,000 of the net proceeds from this offering (or approximately $32,800,000 if the underwriter exercises its option to purchase additional notes in full) to purchase a call spread option with respect to our common stock. See “Call Spread Option” and “Capitalization.” The call spread option is intended to reduce the potential dilution from conversion of the notes.

CALL SPREAD OPTION

       Concurrently with the closing of the offering of the notes, we will purchase from Goldman Sachs Financial Markets, L.P., an affiliate of Goldman, Sachs & Co. (such affiliate being referred to as the “option seller”), a call spread option on our common stock. The call spread option covers approximately 53.1 million shares of our common stock, which is the number of shares that are initially issuable upon conversion of the notes in full. We will pay the option seller an aggregate of approximately $28,500,000 in consideration of their sale of the call spread option. The call spread option is a so-called “European” option, which means that it is exercisable only on its specified expiration date, which will be May 1, 2013.

       The call spread option is designed to mitigate dilution from conversion of the notes to the extent that the market price per share of our common stock at the time of exercise of the call spread option is greater than $5.6465 (the “lower strike price”) and is less than or equal to $6.50575 (the “higher strike price”). The number of shares subject to the call spread option and the lower strike price and higher strike price will be subject to customary adjustments for transactions of this type similar to the conversion price adjustments in the indenture. However, there could be circumstances where the number of shares subject to the call spread option, the lower strike price or the higher strike price are adjusted and the conversion price of the notes is not adjusted.

       If the market value of our common stock at the time of the exercise of the call spread option is above the lower strike price, we will receive from the option seller, for no additional consideration, shares of our common stock valued at an amount equal to the then current market price of our common stock minus the lower strike price, multiplied by the number of shares of common stock underlying the call spread option; provided, however, if the then current market price of our common stock exceeds the higher strike price, this amount will be determined by using the difference between the higher strike price and the lower strike price. Alternatively, and for no additional consideration on our part, we may elect to receive the amount calculated above from the option seller in cash upon our exercise of the option. If the market value of our common stock at the time of exercise of the call spread option is between the lower strike price and the higher strike price, in lieu of the settlement elections above, we may elect to receive from the option seller, upon payment by us of the aggregate exercise price of the option, the full number of shares of common stock underlying the call spread option.

       If the market price of our common stock exceeds the higher strike price at time of exercise of the call spread option, the dilution mitigation under the call spread option will be capped, which means that the call spread option will not mitigate dilution from conversion of the notes to the extent the market price per share of our common stock exceeds $6.50575 at the time of conversion.

       The call spread option is a contract entered into by us with the option seller, and is not part of the terms of the notes and will not affect the holders’ rights under the notes. As a holder of the notes, you will not have any rights with respect to the call spread option.

CAPITALIZATION

       The following table sets forth:

       The table does not take into account any repurchases of our outstanding 3.75% Convertible Notes due February 1, 2008 that we may make from the proceeds of this offering or otherwise. This table should be read in conjunction with our consolidated financial statements and the related notes as filed in our annual report on Form 10-K for our fiscal year ended October 31, 2005 and our quarterly report on Form 10-Q for the fiscal quarter ended January 31, 2006.

DESCRIPTION OF THE NOTES

       The notes will be issued under an indenture to be dated as of April 10, 2006, between us and The Bank of New York, a New York banking corporation (the “trustee”) (the “indenture”). The terms of the notes will include those stated in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”).

       The following description is a summary of the material provisions of the indenture. It does not restate the indenture in its entirety. A copy of the indenture will be filed by us with the SEC and will be available as described under the heading “Where You Can Find More Information” in the prospectus accompanying this prospectus supplement.

Brief Description of the Notes

       The notes will be:

General

       The notes are convertible prior to maturity at the election of the holder (unless earlier redeemed or repurchased) into shares of our common stock at the initial conversion rate of 177.1009 shares of our common stock per $1,000 in principal amount of notes, which is equal to an initial conversion price of approximately $5.65 per share, as described under “— Conversion of Notes.” We are offering $300,000,000 in aggregate principal amount of notes ($345,000,000 aggregate principal amount if the underwriter’s option to purchase additional notes is exercised in full). The notes will be issued only in denominations of $2,000 or in integral multiples of $1,000 in excess thereof. The notes will mature on May 1, 2013, unless earlier redeemed at our option or converted by you or repurchased by us at your option upon a fundamental change.

       Neither we nor our subsidiaries are restricted from paying dividends, incurring debt, granting liens, selling assets or issuing or repurchasing our securities under the indenture. In addition, there are no financial covenants in the indenture.

       The notes will bear interest at the annual rate of 0.25% commencing on the date of issuance. Interest will be payable on May 1 and November 1 of each year, beginning November 1, 2006, subject to limited exceptions if the notes are redeemed, converted or repurchased prior to the interest payment date. The record dates for the payment of interest will be April 15 and October 15. We will not, however, pay accrued interest on any notes that are converted except under the limited circumstances described under “— Conversion Procedures.” We may, at our option, pay interest on the notes by check mailed to the holders. However, beneficial owners of notes issued in global form will be paid by wire transfer in immediately available funds in accordance with DTC’s settlement procedures, and a holder of certificated notes with an aggregate principal amount in excess of $2.0 million will be paid by wire transfer in immediately available funds upon its election if the holder has provided us with wire transfer instructions at least 10 business days prior to the payment date. Interest on the notes will accrue and be paid on the basis of a 360-day year comprised of twelve 30-day months. We will not be required to make any payment on the notes due on any day which is

       We will maintain an office in New York, New York where the notes may be presented for registration, transfer, exchange or conversion. This office will initially be an office or agency of the trustee. Except under limited circumstances described below, the notes will be issued only in fully-registered book entry form, without coupons, and will be represented by one or more global notes. There will be no service charge for any registration of transfer or exchange of notes. We may, however, require holders to pay a sum sufficient to cover any tax or other governmental charge payable in connection with certain transfers or exchanges as described under “— Conversion Procedures.”

Conversion of Notes

       You may convert all or any portion of the principal amount of your notes in integral multiples of $1,000 (provided that the principal amount of any such notes to remain outstanding after such conversion is equal to $2,000 or any integral multiple of $1,000 in excess thereof) into shares of our common stock at any time on or prior to the close of business on the maturity date, unless the notes have been previously redeemed or repurchased. The conversion rate is initially 177.1009 shares of our common stock per $1,000 principal amount of notes (which is equivalent to an initial conversion price of approximately $5.65 per share). The conversion rate in effect at any given time is referred to in this prospectus supplement as the “applicable conversion rate” and will be subject to adjustments as described below under “— Anti-Dilution Adjustments” and “— Adjustment to Conversion Rate Upon a Fundamental Change,” but will not be adjusted for accrued interest. The “applicable conversion price” at any given time is equal to the principal amount of a $1,000 note divided by the applicable conversion rate.

       If you have submitted your notes for repurchase upon a fundamental change, you may only convert your notes if you withdraw your election in accordance with the indenture.

Conversion Procedures

       If you wish to exercise your conversion right, you must deliver an irrevocable conversion notice, together, if the notes are in certificated form, with the certificated security (the date of such delivery of notice and all other requirements for conversion having been satisfied, the “conversion date”), to the conversion agent and us. The conversion agent will, on your behalf, convert the notes into shares of common stock. You may obtain copies of the required form of the conversion notice from the conversion agent. Upon conversion, we will satisfy our conversion obligation with respect to the principal amount of the notes to be converted in shares of our common stock.

       Shares of our common stock deliverable upon conversion will be delivered to the conversion agent no later than the third business day following the conversion date.

       We will not issue fractional shares of our common stock upon conversion of the notes. In lieu of fractional shares otherwise issuable (calculated on an aggregate basis in respect of all the notes you have surrendered for conversion), you will be entitled to receive cash based on the closing sale price of our common stock on the trading day immediately preceding the conversion date.

       Upon conversion of notes, you generally will not receive any cash payment of interest. By delivering to the holder the number of shares of our common stock issuable upon conversion of a note and any cash in lieu of fractional shares of common stock, we will be deemed to have satisfied all of our obligations with respect to such note through the conversion date. That is, we will not pay accrued but unpaid interest, if any, and we will not adjust the conversion rate to account for any accrued interest.

       The term “business day” means any day other than a Saturday, Sunday or a day on which banking institutions in the City of New York, New York are authorized by law, regulation or executive order to remain closed.

       If you convert notes, we will pay any documentary, stamp or similar issue or transfer tax due on the issue of shares of our common stock upon the conversion, unless the tax or duty is due because you request the shares to be issued or delivered in a name other than your own, in which case you will pay the tax or duty. Certificates representing our common stock will be issued or delivered only after all applicable taxes and duties payable by you, if any, have been paid.

Anti-dilution Adjustments

       The applicable conversion rate will be subject to adjustment, without duplication, from time to time, upon the occurrence of any of the following events:

               The “daily adjustment” for any given trading day is equal to a fraction:

        For purposes of this clause (8):

       We may increase the conversion rate as our board of directors considers advisable to avoid or diminish any income tax to holders of our common stock or rights to purchase our common stock resulting from any dividend or distribution of stock or issuance of rights or warrants to purchase or subscribe for stock or from any event treated as such for income tax purposes. We may also, from time to time, to the extent permitted by applicable law, increase the conversion rate by any amount for any period of at least 20 business days if our board of directors has determined that such increase would be in our best interests. If our board of directors makes such a determination, it will be conclusive. We will give you notice at least 15 days prior to the effective date of such change in the conversion rate, with a copy to the trustee and conversion agent, of such an increase in the conversion rate. Any increase, however, will not be taken into account for purposes of determining whether the closing price of our common stock equals or exceeds 105% of the conversion price in connection with an event that otherwise would be a fundamental change as defined below.

       No adjustment to the conversion rate or your ability to convert will be made if you otherwise participate in the distribution without conversion or in certain other cases.

       The applicable conversion rate will not be adjusted:

       We will not be required to make an adjustment in the conversion rate unless the adjustment would require a change of at least 1% in the conversion rate. However, we will carry forward any adjustment that is less than 1% of the conversion rate, take such carried-forward adjustments into account in any subsequent adjustment, and make such carried-forward adjustments, regardless of whether the aggregate adjustment is less than 1%, (a) annually on the anniversary of the first date of issue of the notes and (b) otherwise (1) five business days prior to the stated maturity of the

       Upon conversion of your notes into shares of our common stock, you will also receive the associated rights issued under our Rights Agreement dated December 29, 1997, as amended, or any other stockholder rights plan we may adopt, whether or not the rights have separated from the common stock at the time of conversion unless, prior to conversion, the rights have expired, terminated or been exchanged.

       In the case of consolidations, mergers, conveyances, sales or transfers of all or substantially all of our assets or other transactions that cause our common stock to be converted into the right to receive other securities, cash or property, upon conversion of your notes, you will be entitled to receive the same type of consideration that you would have been entitled to receive if you had converted the notes into our common stock immediately prior to any of these events.

       For purposes of the foregoing, the type and amount of consideration that you would have been entitled to receive as a holder of our common stock in the case of consolidations, mergers, conveyances, sales or transfers of assets or other transactions that cause our common stock to be converted into the right to receive more than a single type of consideration (determined based in part upon any form of stockholder election) will be deemed to be the weighted average of the types and amounts of consideration received by the holders of our common stock that affirmatively make such an election.

Optional Redemption by Ciena

       The notes may not be redeemed prior to May 5, 2009. At any time on or after May 5, 2009, we will have the right, at our option, to redeem the notes in cash, in whole or in part, but only if the closing sale price of our common stock for at least 20 trading days in the 30 consecutive trading day period ending on the date one trading day prior to the day we give a notice of redemption is greater than 130% of the applicable conversion price on the date of such notice, at a redemption price equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, on the principal amount of the notes redeemed to the date of redemption.

       No sinking fund is provided for the notes.

       We may, to the extent permitted by law, at any time, and from time to time, purchase the notes at any price or prices in the open market or otherwise.

Selection and Notice of Redemption

       In the event that less than all of the notes are to be redeemed at any time pursuant to an optional redemption, selection of the notes for redemption will be made by the trustee in compliance with the requirements of the principal national securities exchange, if any, on which such notes are listed or, if such notes are not then listed on a national securities exchange, on a pro rata basis, by lot or by such method as the trustee shall deem fair and appropriate; provided, however, that no notes of a principal amount of $1,000 or less shall be redeemed in part.

       Notice of redemption will be mailed by first-class mail, given electronically or by any other means approved by the trustee, at least 30 but not more than 60 days before the redemption date to each holder of notes to be redeemed at its registered address. If any note is to be redeemed in part only, the notice of redemption that relates to that note will state the portion of the principal amount of the note to be redeemed. A note in a principal amount equal to the unredeemed portion of the note will be issued in the name of the holder of the note upon cancellation of the original note. On

Repurchase at Option of the Holder Upon a Fundamental Change

       If a fundamental change (as defined below) occurs at any time prior to stated maturity, you may have the right to require us to purchase any or all of your notes for cash, at a price equal to 100% of the principal amount of the notes to be repurchased plus accrued and unpaid interest, if any, to (but not including) the fundamental change repurchase date, unless such repurchase date falls after a regular record date and on or prior to the corresponding interest payment date, in which case we will pay the full amount of accrued and unpaid interest payable on such interest payment date to the holder of record at the close of business on the corresponding regular record date. For a discussion of the U.S. federal income tax treatment of a holder receiving cash, see “Important United States Federal Income Tax Consequences.”

       A “fundamental change” will be deemed to have occurred at the time after the notes are originally issued that any of the following occurs:

       However, notwithstanding the foregoing, holders of the notes will not have the right to require us to repurchase any notes under clauses (2), (3) or (4) above (and we will not be required to deliver the fundamental change repurchase right notice incidental thereto), if either:

       For purposes of these provisions, whether a person is a “beneficial owner” will be determined in accordance with Rule 13d-3 under the Exchange Act, and “person” includes any syndicate or group that would be deemed to be a “person” under Section 13(d)(3) of the Exchange Act.

       The term “continuing directors” means, as of any date of determination, any member of our board of directors who (a) was a member of our board of directors on the date of the indenture or (b) becomes a member of our board of directors subsequent to that date and was appointed, nominated for election or elected to our board of directors with the approval of (1) a majority of the continuing directors who were members of our board of directors at the time of such appointment, nomination or election or (2) a majority of the continuing directors that were serving at the time of such appointment, nomination or election on a committee of our board of directors that appointed or nominated for election or reelection such board member.

       The term “capital stock” means (a) in the case of a corporation, corporate stock, (b) in the case of an association or business entity, shares, interests, participations, rights or other equivalents (however designated) of corporate stock, (c) in the case of a partnership or limited liability company, partnership or membership interests (whether general or limited) and (d) any other interest or participation that confers on a person the right to receive a share of the profits and losses of, or distribution of the assets of, the issuing person.

       At least 20 business days prior to the anticipated date on which a fundamental change will become effective (or if we do not have actual notice of a fundamental change 20 business days prior to the effective date, as soon as we have actual notice of the fundamental change), we will provide to all holders of the notes, the trustee, the paying agent and the conversion agent a notice (the “fundamental change notice”) stating:

       In addition to the fundamental change notice, on or before the 20th trading day after the date on which a fundamental change transaction becomes effective (which fundamental change results in the holders of notes having the right to cause us to repurchase their notes), we will provide to all holders of the notes and the trustee and paying agent and conversion agent a notice of the occurrence of the fundamental change and of the resulting repurchase right (the “fundamental change repurchase right notice”).

       To exercise the fundamental change repurchase right, you must deliver, before the close of business on the second business day immediately preceding the repurchase date, the notes to be repurchased, together with the repurchase notice duly completed, to the paying agent. Your repurchase notice must state:

       If the notes are not in certificated form, your fundamental change repurchase notice must comply with appropriate DTC procedures.

       If you exercise your right to have any portion of your note repurchased, you may not surrender that portion of your note for conversion unless you withdraw your repurchase notice in accordance with the indenture. You may withdraw any such repurchase notice (in whole or in part) by a written notice of withdrawal delivered to the paying agent prior to 5:00 p.m., New York City time, on the second business day prior to the repurchase date. The notice of withdrawal must state:

       If the notes are not in certificated form, the notice of withdrawal must comply with appropriate DTC procedures.

       We will be required to repurchase the notes on a date chosen by us in our sole discretion that is no less than 20 and no more than 35 business days after the date of our mailing of the relevant fundamental change repurchase right notice, subject to extension to comply with applicable law. To receive payment of the repurchase price, you must either effect book-entry transfer or deliver the notes, together with necessary endorsements, to the office of the paying agent after delivery of the repurchase notice. Holders will receive payment of the repurchase price promptly following the later of the repurchase date or the time of book-entry transfer or the delivery of the notes. If the paying

       We will under the indenture:

Adjustment to Conversion Rate Upon a Fundamental Change

       If and only to the extent that you convert your notes in connection with a fundamental change described in clause (2), (3) or (4) of the definition of fundamental change, we will increase the conversion rate for the notes surrendered for conversion by a number of additional shares (the “additional shares”) as described below; provided, however, that no increase will be made in the case of a fundamental change if at least 90% of the consideration paid for our common stock (excluding cash payments for fractional shares and cash payments made pursuant to dissenters’ appraisal rights) in such fundamental change transaction consists of shares of capital stock traded on the New York Stock Exchange or another U.S. national securities exchange or quoted on The Nasdaq Stock Market or another established automated over-the-counter trading market in the United States (or that will be so traded or quoted immediately following the transaction) and as a result of such transaction or transactions the notes become convertible solely into such common stock.

       The number of additional shares will be determined by reference to the table below, based on the effective date of the fundamental change and the price (the “stock price”) paid per share for our common stock in such fundamental change transaction. If holders of our common stock receive only cash in such fundamental change transaction, the stock price will be the cash amount paid per share. Otherwise, the stock price will be the average of the last closing sale prices of our common stock on each of the five consecutive trading days prior to but not including the effective date of such fundamental change.

       A conversion of notes by a holder will be deemed for these purposes to be “in connection with” a fundamental change if the conversion notice is received by the conversion agent on or after the effective date of the fundamental change and prior to the 45th day following the effective date of the fundamental change (or, if earlier and to the extent applicable, the close of business on the second business day immediately preceding the fundamental change repurchase date (as specified in the fundamental change repurchase right notice described under “— Repurchase at Option of the Holder Upon a Fundamental Change”)).

       The stock prices set forth in the first row of the following table (i.e., the column headers) will be adjusted as of any date on which the conversion rate of the notes is adjusted, as described above under “— Anti-dilution Adjustments.” The adjusted stock prices will equal the stock prices applicable immediately prior to such adjustment, multiplied by an adjustment factor equal to a fraction, the numerator of which is the conversion rate immediately prior to the adjustment giving rise to the stock price adjustment and the denominator of which is the conversion rate as so adjusted. The number of

       The following table sets forth the hypothetical increase in the conversion rate, expressed as a number of additional shares issuable per $1,000 initial principal amount of notes as a result of a fundamental change that occurs in the corresponding period:

       The stock prices and additional share amounts set forth above are based upon a closing sale price of $4.91 on April 4, 2006 and an initial conversion rate of 177.1009 shares of our common stock per $1,000 in principal amount of notes, which is equal to an initial conversion price of approximately $5.65 per share.

       The exact stock price and conversion dates may not be set forth in the table in which case, if the stock price is:

       Notwithstanding the foregoing, in no event will the total number of shares issuable upon conversion of a note exceed 203.6660 per $1,000 initial principal amount of the notes, after giving effect to the increase in the conversion rate described above, subject to anti-dilution adjustments described under “— Anti-dilution Adjustments.”

Consolidation, Merger and Sale of Assets

       We may not, directly or indirectly, consolidate with or merge into any person in a transaction in which we are not the surviving corporation or convey, transfer or lease our properties and assets substantially as an entirety to any successor person, unless:

       Notwithstanding the foregoing, we may merge with an affiliate solely for the purpose of reincorporating in another jurisdiction.

       Each of the following is an “event of default” under the indenture:

       If an event of default, other than an event of default described in clause (9) above with respect to us, occurs and is continuing, either the trustee or the holders of at least 25% in aggregate principal amount of the outstanding notes may declare the principal amount of the notes to be due and payable immediately. However, after such acceleration, provided that such rescission would not conflict with any judgment or decree of a court of competent jurisdiction, the holders of a majority in aggregate principal amount of outstanding notes may, under certain circumstances, rescind and annul the acceleration if all events of default, other than the non-payment of principal or interest of notes that have become due solely by such declaration of acceleration, have been cured or waived as provided in the indenture. If an event of default arising from events of bankruptcy, insolvency or reorganization with respect to us occurs, then the principal of, and accrued interest on, all the notes will automatically become immediately due and payable without any declaration or other act on the part of the holders of the notes or the trustee. For information as to waiver of defaults, see “— Modification and Waiver” below.

       In the event of a declaration of acceleration of the notes because an event of default described in clause (7) has occurred and is continuing, the declaration of acceleration of the notes shall be automatically annulled if such event of default triggering such declaration of acceleration pursuant to

       Subject to the trustee’s duties in the case of an event of default, the trustee will not be obligated to exercise any of its rights or powers at the request of the holders, unless the holders have offered to the trustee reasonable indemnity. Subject to the indenture, applicable law and the trustee’s indemnification, the holders of a majority in aggregate principal amount of the outstanding notes will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to the notes.

       No holder will have any right to institute any proceeding under the indenture, or for the appointment of a receiver or a trustee, or for any other remedy under the indenture unless:

       However, the above limitations do not apply to a suit instituted by a holder for the enforcement of payment of the principal of or interest on any note on or after the applicable due date or the right to convert the note in accordance with the indenture.

       Generally, the holders of a majority of the aggregate principal amount of outstanding notes may waive any default or event of default unless:

       We are required to furnish to the trustee, on an annual basis, an officer’s certificate as to whether or not Ciena, to such officers’ knowledge, is in default in the performance or observance of any of the terms, provisions and conditions of the indenture, specifying any known defaults.

Modification and Waiver

       We and the trustee may amend or supplement the indenture or the notes with the consent of the holders of a majority in aggregate principal amount of the outstanding notes. In addition, the holders of a majority in aggregate principal amount of the outstanding notes may waive our compliance in any instance with any provision of the indenture without notice to the note holders. However, no amendment, supplement or waiver may be made without the consent of the holder of each outstanding note if such amendment, supplement or waiver would:

       We and the trustee may amend or supplement the indenture or the notes without notice to, or the consent of, the note holders to, among other things, cure any ambiguity, defect or inconsistency or make any other change that does not adversely affect the rights of any note holder in any material respect.

Satisfaction and Discharge

       We may discharge our obligations under the indenture while notes remain outstanding if all outstanding notes have or will become due and payable at their scheduled maturity within one year or are to be called for redemption within one year and we have deposited with the trustee or a paying agent an amount sufficient to pay and discharge all outstanding notes; provided, however, that the foregoing will not discharge our obligation to effect conversion, registration of transfer or exchange of securities in accordance with the terms of the indenture.

Transfer and Exchange

       We have initially appointed the trustee as the security registrar, paying agent and conversion agent, acting through its corporate trust office. We reserve the right to:

Purchase and Cancellation

       All notes surrendered for payment, registration of transfer or exchange or conversion will, if surrendered to any person other than the trustee, be delivered to the trustee. All notes delivered to the trustee will be cancelled promptly by the trustee. No notes will be authenticated in exchange for any notes cancelled as provided in the indenture.

       We may, to the extent permitted by law, at any time, and from time to time, repurchase notes in the open market or otherwise at any price or prices. Any notes repurchased by us may, to the extent permitted by law, be reissued or resold or may, at our option, be surrendered to the trustee for cancellation. Any notes surrendered for cancellation may not be reissued or resold and will be promptly cancelled. Any notes held by us or one of our subsidiaries will be disregarded for voting

Replacement of Notes

       We will replace mutilated, destroyed, stolen or lost notes at your expense upon delivery to the trustee of the mutilated notes, or evidence of the loss, theft or destruction of the notes satisfactory to us and the trustee. In the case of a lost, stolen or destroyed note, indemnity satisfactory to the trustee and us may be required at the expense of the holder of such note before a replacement note will be issued.

Calculations in Respect of the Notes

       We will be responsible for making many of the calculations called for under the notes. These calculations include, but are not limited to, determination of the closing sale price of our common stock in the absence of reported or quoted prices and adjustments to the conversion rate. We will make all these calculations in good faith and, absent manifest error, our calculations will be final and binding on the holders of notes. We will provide a schedule of our calculations to the trustee, and the trustee is entitled to rely conclusively on the accuracy of our calculations without independent verification.

No Personal Liability of Directors, Officers, Employees or Stockholders

       No director, officer, employee, incorporator or stockholder of Ciena, as such, will have any liability for any obligations of Ciena under the notes or the indenture or for any claim based on, in respect of, or by reason of, such obligations or their creation. Each holder of notes by accepting a note waives and releases all such liability. The waiver and release are part of the consideration for issuance of the notes. The waiver may not be effective to waive liabilities under the federal securities laws.

Governing Law

       The indenture and the notes will be governed by, and construed in accordance with, the laws of the State of New York.

Concerning the Trustee

       The Bank of New York has agreed to serve as the trustee under the indenture. The trustee will be permitted to deal with us and any of our affiliates with the same rights as if it were not trustee. However, under the Trust Indenture Act, if the trustee acquires any conflicting interest and there exists a default with respect to the notes, the trustee must eliminate such conflict or resign.

       The holders of a majority in principal amount of all outstanding notes will have the right to direct the time, method and place of conducting any proceeding for exercising any remedy or power available to the trustee. However, any such direction may not conflict with any law or the indenture, may not be unduly prejudicial to the rights of another holder or the trustee and may not involve the trustee in personal liability.

Book-Entry, Delivery and Form

       We will initially issue the notes in the form of one or more global securities. The global security will be deposited with the trustee as custodian for DTC and registered in the name of a nominee of DTC. Except as set forth below, the global security may be transferred, in whole and not in part, only to DTC or another nominee of DTC. You will hold your beneficial interests in the global security directly through DTC if you have an account with DTC or indirectly through organizations that have

       DTC has advised us that it is:

       DTC was created to hold securities of institutions that have accounts with DTC, called “participants” and to facilitate the clearance and settlement of securities transactions among its participants in such securities through electronic book-entry changes in accounts of the participants, thereby eliminating the need for physical movement of securities certificates. DTC’s participants include securities brokers and dealers, which may include the underwriter, banks, trust companies, clearing corporations and certain other organizations. Access to DTC’s book-entry system is also available to others such as banks, brokers, dealers and trust companies, called “indirect participants,” that clear through or maintain a custodial relationship with a participant, whether directly or indirectly.

       We expect that pursuant to procedures established by DTC upon the deposit of the global security with DTC, DTC will credit, on its book-entry registration and transfer system, the principal amount of notes represented by such global security to the accounts of participants. The accounts to be credited will be designated by the underwriter. Ownership of beneficial interests in the global security will be limited to participants or persons that may hold interests through participants. Ownership of beneficial interests in the global security will be shown on, and the transfer of those beneficial interests will be effected only through, records maintained by DTC (with respect to participants’ interests), the participants and the indirect participants. The laws of some jurisdictions may require that certain purchasers of securities take physical delivery of such securities in definitive form. These limits and laws may impair the ability to transfer or pledge beneficial interests in the global security.

       Owners of beneficial interests in global securities who desire to convert their interests into common stock should contact their brokers or other participants or indirect participants through whom they hold such beneficial interests to obtain information on procedures, including proper forms and cutoff times, for submitting requests for conversion.

       So long as DTC, or its nominee, is the registered owner or holder of a global security, DTC or its nominee, as the case may be, will be considered the sole owner or holder of the notes represented by the global security for all purposes under the indenture and the notes. In addition, no owner of a beneficial interest in a global security will be able to transfer that interest except in accordance with the applicable procedures of DTC. Except as set forth below, as an owner of a beneficial interest in the global security, you will not be entitled to have the notes represented by the global security registered in your name, will not receive or be entitled to receive physical delivery of certificated securities and will not be considered to be the owner or holder of any notes under the global security. We understand that under existing industry practice, if an owner of a beneficial interest in the global security desires to take any action that DTC, as the holder of the global security, is entitled to take, DTC would authorize the participants to take such action. Additionally, in such case, the participants would authorize beneficial owners owning through such participants to take such action or would otherwise act upon the instructions of beneficial owners owning through them.

       We will make payments of principal of and interest on the notes represented by the global security registered in the name of and held by DTC or its nominee to DTC or its nominee, as the

       We expect that DTC or its nominee, upon receipt of any payment of principal of or interest on the global security, will credit participants’ accounts with payments in amounts proportionate to their respective beneficial interests in the principal amount of the global security as shown on the records of DTC or its nominee. We also expect that payments by participants or indirect participants to owners of beneficial interests in the global security held through such participants or indirect participants will be governed by standing instructions and customary practices and will be the responsibility of such participants or indirect participants. We will not have any responsibility or liability for any aspect of the records relating to, or payments made on account of, beneficial interests in the global security for any note or for maintaining, supervising or reviewing any records relating to such beneficial interests or for any other aspect of the relationship between DTC and its participants or indirect participants or the relationship between such participants or indirect participants and the owners of beneficial interests in the global security owning through such participants.

       Transfers between participants in DTC will be effected in the ordinary way in accordance with DTC rules and will be settled in same-day funds.

       DTC has advised us that it will take any action permitted to be taken by a holder of notes only at the direction of one or more participants to whose account the DTC interests in the global security is credited and only in respect of such portion of the aggregate principal amount of notes as to which such participant or participants has or have given such direction. However, if DTC notifies us that it is unwilling to be a depositary for the global security or ceases to be a clearing agency or there is an event of default under the notes, DTC will exchange the global security for certificated securities which it will distribute to its participants. Although DTC is expected to follow the foregoing procedures in order to facilitate transfers of interests in the global security among participants of DTC, it is under no obligation to perform or continue to perform such procedures, and such procedures may be discontinued at any time. Neither we nor the trustee will have any responsibility, or liability for the performance by DTC or the participants or indirect participants of their respective obligations under the rules and procedures governing their respective operations.

IMPORTANT UNITED STATES FEDERAL INCOME TAX CONSEQUENCES

       This section describes the material United States federal income tax considerations relating to the purchase, ownership and disposition of the notes and of the common stock acquired upon conversion of the notes. This description does not provide a complete analysis of all potential tax considerations. The information provided below is based on the Internal Revenue Code of 1986, as amended, referred to as the “Code,” Treasury regulations issued under the Code, published rulings and court decisions, all as in effect on the date hereof. These authorities may change, possibly on a retroactive basis, or the Internal Revenue Service, referred to as the “IRS,” might interpret the existing authorities differently. In either case, the tax consequences of purchasing, owning or disposing of the notes or our common stock could differ from those described below.

       As used herein, “U.S. Holder” means a beneficial owner of the notes or the common stock who or which is:

       As used herein, a “Non-U.S. Holder” means a beneficial owner of the notes or the common stock who or which is a nonresident alien or a corporation, trust or estate for U.S. federal income tax purposes that is not a U.S. Holder.

       If a partnership or other entity taxable as a partnership holds the notes or the common stock, the tax treatment of a partner will generally depend on the status of the partner and the activities of the partnership. Any such partnership or other entity owning the notes or the common stock, and any owner of an interest in any such partnership or other entity, should consult its own tax advisor as to the tax consequences of the purchase, ownership and disposition of the notes and the common stock.

       This description generally applies only to investors that purchase notes for cash in the initial offering at their issue price, which is the first price at which a substantial amount of the notes are sold for money to the public (not including sales to bond houses, brokers or similar persons or organizations acting in the capacity of underwriters, placement agents or wholesalers), and that hold the notes and common stock as “capital assets” (generally, for investment). This description is general in nature and does not discuss all aspects of U.S. federal income taxation that may be relevant to a particular holder in light of the holder’s particular circumstances, or to certain types of holders subject to special treatment under U.S. federal income tax laws (such as financial institutions, real estate investment trusts, regulated investment companies, grantor trusts, insurance companies, tax-exempt organizations, brokers, dealers or traders in securities or foreign currencies, and persons holding notes or common stock as part of a position in a “’straddle” or as part of a “hedging,” “conversion” or “integrated” transaction for U.S. federal income tax purposes). In addition, this description does not consider the effect of any foreign, state, local or other tax laws, or any U.S. tax considerations (e.g., estate or gift tax) other than U.S. federal income tax considerations, that may be applicable to particular holders.

       We urge prospective investors to consult their own tax advisors with respect to the application of the U.S. federal income tax laws to their particular situations as well as any tax consequences arising under the U.S. federal estate or gift tax laws or under the laws of any state, local or foreign taxing jurisdiction or under any applicable treaty or the possible effects of changes in the United States federal and other tax laws.

Consequences to U.S. Holders

       The following is a summary of the U.S. federal income tax consequences that apply to U.S. Holders of notes or common stock.

Interest

       Stated interest on the notes will generally be included in a U.S. Holder’s gross income as ordinary income for U.S. federal income tax purposes at the time it is received or accrued in accordance with the U.S. Holder’s regular method of accounting.

Sale, Exchange or Redemption of the Notes

       A U.S. Holder generally will recognize capital gain or loss if the U.S. Holder disposes of a note in a sale, redemption or exchange (other than a conversion of the note into common stock). The U.S. Holder’s gain or loss will equal the difference between the amount realized by the U.S. Holder

       A U.S. Holder’s adjusted tax basis in a note will generally equal the amount the U.S. Holder paid for the note if the U.S. Holder is a cash basis taxpayer. The amount realized by the U.S. Holder will include the amount of any cash and the fair market value of any other property received for the note.

       Gain or loss recognized by a U.S. Holder on a disposition of the note will be long-term capital gain or loss if the U.S. Holder held the note for more than one year. Long-term capital gains of non-corporate taxpayers are taxed at lower rates than those applicable to ordinary income. The deductibility of capital losses is subject to certain limitations.

Conversion of the Notes

       A U.S. Holder who converts a note into our common stock will not recognize any income, gain or loss, except for any gain or loss attributable to the receipt of cash in lieu of a fractional share. The U.S. Holder’s aggregate adjusted basis in the common stock will equal its adjusted basis in the note (less the portion of the basis allocable to a fractional share of common stock for which cash is received), and the U.S. Holder’s holding period for the stock will include the period during which the U.S. Holder held the note. The receipt of cash in lieu of a fractional share of common stock generally will result in capital gain or loss measured by the difference between the cash received for the fractional share and the U.S. Holder’s adjusted tax basis allocable to such fractional share.

Dividends on Common Stock

       If a U.S. Holder converts a note into common stock and we make a distribution (other than certain distributions of our own stock) in respect of that stock, the distribution will be treated as a dividend to the extent it is paid from our current or accumulated earnings and profits. If the distribution exceeds our current and accumulated earnings and profits, the excess will be treated as a nontaxable return of capital reducing the U.S. Holder’s adjusted tax basis in the U.S. Holder’s common stock to the extent of the U.S. Holder’s adjusted tax basis in that stock. Any remaining excess will be treated as capital gain.

       Recent legislation provides for special treatment of dividends paid to individual taxpayers in taxable years beginning before January 1, 2009. Under this legislation, dividend income that is received by individual taxpayers and that satisfies certain requirements is generally subject to tax at a favorable rate. We are required to provide stockholders who receive dividends with an information return on Form 1099-DIV that states the extent to which the dividend is paid from our current or accumulated earnings and profits.

       If a U.S. Holder is a U.S. corporation, it will be able to claim the deduction allowed to U.S. corporations in respect of dividends received from other U.S. corporations equal to a portion of any dividends received, subject to generally applicable limitations on that deduction. In general, a dividend distribution to a corporate U.S. Holder may qualify for the 70% dividends received deduction if the U.S. Holder owns less than 20% of the voting power and value of our stock.

Constructive Dividends to Holders of Notes or Common Stock

       The terms of the notes allow for changes in the conversion price of the notes in certain circumstances. A change in conversion price that allows U.S. Holders of notes to receive more shares of common stock on conversion may increase those note holders’ proportionate interests in our earnings and profits or assets. In that case, those note holders could be treated as though they

Sale of Common Stock

       A U.S. Holder will generally recognize capital gain or loss on a sale or exchange of common stock. The U.S. Holder’s gain or loss will equal the difference between the amount realized by the U.S. Holder and the U.S. Holder’s adjusted tax basis in the stock. The amount realized by the U.S. Holder will include the amount of any cash and the fair market value of any other property received for the stock. A U.S. Holder’s adjusted tax basis in common stock received upon conversion of a note will generally be as described above in “— Conversion of the Notes.” Gain or loss recognized by a U.S. Holder on a sale or exchange of common stock will be long-term capital gain or loss if the U.S. Holder held the stock for more than one year. Long-term capital gains of non-corporate taxpayers are taxed at lower rates than those applicable to ordinary income. The deductibility of capital losses is subject to certain limitations.

Information Reporting and Backup Withholding

       When required, we or our paying agent will report to the holders of the notes and the common stock and the IRS amounts paid or accrued on or with respect to the notes and the common stock during each calendar year and the amount of tax, if any, withheld from such payments. A U.S. Holder may be subject to backup withholding on payments made on the notes and dividends paid on the common stock, and on the proceeds from a sale of the notes or the common stock, at the applicable rate (which is currently 28%) if the U.S. Holder (a) fails to provide us or our paying agent (or the broker or other relevant paying agent) with a correct taxpayer identification number or certification of exempt status (such as certification of corporate status), (b) has been notified by the IRS that it is subject to backup withholding as a result of the failure to properly report payments of interest or dividends or (c) in certain circumstances, has failed to certify under penalties of perjury that it is not subject to backup withholding. A U.S. Holder may be eligible for an exemption from backup withholding by providing a properly completed IRS Form W-9. Any amounts withheld under the backup withholding rules will generally be allowed as a refund or a credit against a U.S. Holder’s United States federal income tax liability provided the required information is properly furnished to the IRS on a timely basis.

Consequences to Non-U.S. Holders

       The following is a summary of the U.S. federal income tax consequences that apply to Non-U.S. Holders of notes or common stock. Special rules may apply to certain Non-U.S. Holders such as “controlled foreign corporations,” “passive foreign investment companies,” “foreign personal holding companies,” certain United States expatriates and investors in entities that are treated as

Interest

       Interest paid to a Non-U.S. Holder of the notes will not be subject to United States federal withholding tax under the “portfolio interest exception,” provided that:

       Interest paid to a Non-U.S. Holder that does not qualify for the portfolio interest exception and that is not effectively connected to a United States trade or business will be subject to United States federal withholding tax at a rate of 30%, unless a United States income tax treaty applies to reduce or eliminate withholding.

       A Non-U.S. Holder will generally be subject to tax in the same manner as a U.S. Holder with respect to interest that is effectively connected with the conduct of a trade or business by the Non-U.S. Holder in the United States and, if an applicable tax treaty so provides, such interest is attributable to a United States permanent establishment maintained by the Non-U.S. Holder. Such effectively connected interest received by a Non-U.S. Holder that is a corporation may in certain circumstances be subject to an additional “branch profits tax” at a 30% rate or, if applicable, a lower treaty rate.

       To claim the benefit of a lower treaty rate or to claim exemption from withholding because the interest is effectively connected with a United States trade or business, a Non-U.S. Holder must provide a properly executed IRS Form W-8BEN or IRS Form W-8ECI (or a suitable substitute form), as applicable. Such certificate must contain, among other information, the name and address of the Non-U.S. Holder.

       Non-U.S. Holders should consult their own tax advisors regarding applicable income tax treaties, which may provide different rules.

Conversion of the Notes

       A Non-U.S. Holder who converts a note into common stock will not recognize any income, gain or loss, except for any gain or loss attributable to the receipt of cash in lieu of a fractional share. Cash received in lieu of a fractional share on conversion may give rise to gain that would be subject to the rules described below with respect to the sale or exchange of a note or common stock. The Non-U.S. Holder’s aggregate adjusted basis in the common stock will equal the Non-U.S. Holder’s adjusted basis in the note (less the portion of the basis allocable to a fractional share of common stock for which cash is received), and the Non-U.S. Holder’s holding period for the stock will include the period during which the Non-U.S. Holder held the note.

       Subject to the discussion below of backup withholding, dividends paid on the common stock to a Non-U.S. Holder (including any deemed dividend payments as discussed in “Consequences to U.S. Holders — Constructive Dividends to Holders of Notes or Common Stock”) generally will be subject to a 30% U.S. federal withholding tax, unless either: (a) an applicable income tax treaty reduces or eliminates such tax, and the Non-U.S. Holder claims the benefit of that treaty by providing a properly completed and duly executed IRS Form W-8BEN (or suitable successor or substitute form) establishing qualification for benefits under the treaty, or (b) the dividend is effectively connected with the Non-U.S. Holder’s conduct of a trade or business in the United States and the Non-U.S. Holder provides an appropriate statement to that effect on a properly completed and duly executed IRS Form W-8ECI (or suitable successor form).

       If dividends paid on the common stock to a Non-U.S. Holder are effectively connected with the Non-U.S. Holder’s trade or business in the United States, the Non-U.S. Holder will be required to pay United States federal income tax on that dividend on a net income basis generally in the same manner as a U.S. Holder. If a Non-U.S. Holder is eligible for the benefits of a tax treaty between the United States and its country of residence, any dividend income that is effectively connected with a United States trade or business will be subject to United States federal income tax in the manner specified by the treaty and generally will only be subject to such tax if such income is attributable to a permanent establishment (or a fixed base in the case of an individual) maintained by the Non-U.S. Holder in the United States and the Non-U.S. Holder claims the benefit of the treaty by properly submitting an IRS Form W-8BEN. In addition, a Non-U.S. Holder that is treated as a foreign corporation for United States federal income tax purposes may be subject to a branch profits tax equal to 30% (or lower applicable treaty rate) of its earnings and profits for the taxable year, subject to adjustments, that are effectively connected with its conduct of a trade or business in the United States.

Dispositions of Notes and Common Stock

       Generally, a Non-U.S. Holder will not be subject to federal income tax on gain realized upon the sale, exchange, redemption, conversion or other disposition of a note or common stock unless: (a) such holder is an individual present in the United States for 183 days or more in the taxable year of the sale, exchange, redemption or other disposition and certain other conditions are met, (b) the gain is effectively connected with the conduct of a trade or business in the United States by the Non-U.S. Holder, and if an applicable income tax treaty so provides, the gain is attributable to a permanent establishment (or in the case of an individual, to a fixed base) in the United States, or (c) we are or have been a U.S. real property holding corporation, as defined in the Code, at any time within the 5-year period preceding the disposition or the Non-U.S. Holder’s holding period, whichever period is shorter. In the case of a disposition of our common stock, even if we were a U.S. real property holding corporation, such gain would not be taxable under the rules described in clause (c) in the preceding sentence if the common stock is regularly traded on an established securities market and the Non-U.S. holder owns no more than 5% of our common stock. We are not, and do not anticipate becoming, a U.S. real property holding corporation.

       If the first exception (i.e., for an individual present in the United States for 183 days or more in the taxable year of the disposition) applies, the Non-U.S. Holder generally will be subject to tax at a rate of 30% on the amount by which the Non-U.S. Holder’s United States-source capital gains for the taxable year of the disposition exceed its capital losses allocable to United States sources for such year.

       If the second exception (i.e., for gain that is effectively connected with the conduct of a United States trade or business) applies, the Non-U.S. Holder will be required to pay United States federal income tax on the net gain derived from the disposition in the same manner as U.S. Holders, as described above. If a Non-U.S. Holder is eligible for the benefits of a tax treaty between the United

Information Reporting and Backup Withholding

       When required, we or our paying agent will report to the IRS and to each Non-U.S. Holder any amount paid with respect to the notes and the amount of any dividend paid on the common stock in each calendar year, and the amount of tax withheld, if any, with respect to these payments.

       Non-U.S. Holders who have provided the forms and certification mentioned above or who have otherwise established an exemption will generally not be subject to backup withholding tax if neither we nor our agent has actual knowledge or reason to know that any information in those forms and certification is unreliable or that the conditions of the exemption are in fact not satisfied. Payments of the proceeds from the sale of a note or common stock effected outside the United States by or through a foreign office of a broker generally will not be subject to information reporting or backup withholding. However, information reporting, but not backup withholding, may apply to those payments if the broker is, for United States federal income tax purposes, one of the following: (a) a United States person, (b) a controlled foreign corporation, (c) a foreign person 50 percent or more of whose gross income from all sources for the three-year period ending with the close of its taxable year preceding the payment was effectively connected with a United States trade or business, (d) a foreign partnership with specified connections to the United States, or (e) a U.S. branch of a foreign bank or insurance company.

       Payment of the proceeds from a sale of a note or common stock to or through the United States office of a broker will be subject to information reporting and backup withholding unless the beneficial owner certifies as to its taxpayer identification number or otherwise establishes an exemption from information reporting and backup withholding.

       Backup withholding is not an additional tax. The amount of any backup withholding from a payment to a Non-U.S. Holder will be allowed as a credit against such holder’s United States federal income tax liability and may entitle the holder to a refund, provided the required information is furnished to the IRS on a timely basis.

       The preceding discussion of certain U.S. federal income tax consequences is for general information only and is not tax advice. Accordingly, each investor should consult its own tax advisor as to particular tax consequences to it of purchasing, holding and disposing of the notes and the common stock, including the applicability and effect of any state, local or foreign tax laws, and of any proposed changes in applicable laws.

UNDERWRITING

       We and Goldman, Sachs & Co. have entered into an underwriting agreement with respect to the notes being offered. Subject to certain conditions, Goldman, Sachs & Co. has agreed to purchase $300,000,000 aggregate principal amount of the notes.

       Goldman, Sachs & Co. is committed to take and pay for all of the notes being offered, if any are taken, other than the notes covered by the option described below unless and until this option is exercised.

       If Goldman, Sachs & Co. sells more notes than the $300,000,000 aggregate principal amount, Goldman, Sachs & Co. has an option to buy up to an additional $45,000,000 aggregate principal amount of notes from us to cover such sales. Goldman, Sachs & Co. may exercise that option for 13 days.

       The following table shows the per note and total underwriting discounts and commissions to be paid to Goldman, Sachs & Co. Such amounts are shown assuming both no exercise and full exercise of Goldman, Sachs & Co.’s option to purchase an additional $45,000,000 aggregate principal amount of notes.

       We and our executive officers and directors have agreed with Goldman, Sachs & Co. not to dispose of or hedge any of our common stock or securities convertible into or exchangeable for notes of common stock during the period from the date of this prospectus continuing through the date 60 days after the date of this prospectus; however, these agreements are subject to a number of significant exceptions and, in any event, may be waived with the prior written consent of Goldman, Sachs & Co.

       We intend to use a portion of the net proceeds of this offering to purchase a call spread option, the exposure for which will be held by GSFM, an affiliate of Goldman, Sachs & Co. In connection with this call spread option, GSFM will enter into various derivative transactions prior to, at or after the pricing of the notes. See “Call Spread Option” and “Capitalization.” Such hedging arrangements could increase the price of our common stock. GSFM or any transferee of any of its positions, is likely to modify its hedge position from time to time during the term of the call spread option, by purchasing or selling shares of our common stock, our other securities or other instruments it may wish to use in connection with such hedging. The effect, if any, of these transactions and activities on the market price of our common stock or the notes will depend in part on market conditions and the settlement methods under the call spread option and cannot be ascertained at this time, but any of these activities may adversely affect the value of the notes and our common stock, and as a result, the value or amount of the common stock you will receive upon the conversion of the notes.

       These activities by Goldman, Sachs & Co. may stabilize, maintain or otherwise affect the market price of the notes. As a result, the price of the notes may be higher than the price that otherwise might exist in the open market. If these activities are commenced, they may be discontinued by Goldman, Sachs & Co. at any time. These transactions may be effected in the over-the-counter market or otherwise.

       Goldman, Sachs & Co. has represented and agreed that:

       In relation to each Member State of the European Economic Area which has implemented the Prospectus Directive (each, a Relevant Member State), Goldman, Sachs & Co. has represented and agreed that with effect from and including the date on which the Prospectus Directive is implemented in that Relevant Member State (the Relevant Implementation Date) it has not made and will not make an offer of notes to the public in that Relevant Member State prior to the publication of a prospectus in relation to the notes which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Directive, except that it may, with effect from and including the Relevant Implementation Date, make an offer of notes to the public in that Relevant Member State at any time:

       The notes may not be offered or sold by means of any document other than to persons whose ordinary business is to buy or sell shares or debentures, whether as principal or agent, or in circumstances which do not constitute an offer to the public within the meaning of the Companies Ordinance (Cap. 32) of Hong Kong, and no advertisement, invitation or document relating to the notes may be issued, whether in Hong Kong or elsewhere, which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to notes which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap. 571) of Hong Kong and any rules made thereunder.

       This prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the notes may not be circulated or distributed, nor may the notes be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions, specified in Section 275 of the SFA or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

       Where the notes are subscribed or purchased under Section 275 by a relevant person which is: (a) a corporation (which is not an accredited investor) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor, or (b) a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary is an accredited investor, shares, debentures and units of shares and debentures of that corporation or the beneficiaries’ rights and interest in that trust shall not be transferable for 6 months after that corporation or that trust has acquired the notes under Section 275 except: (1) to an institutional investor under Section 274 of the SFA or to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions, specified in Section 275 of the SFA; (2) where no consideration is given for the transfer; or (3) by operation of law.

       The notes have not been and will not be registered under the Securities and Exchange Law of Japan (the Securities and Exchange Law) and Goldman, Sachs & Co. has agreed that it will not offer or sell any notes, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to a resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the Securities and Exchange Law and any other applicable laws, regulations and ministerial guidelines of Japan.

       We have agreed to indemnify Goldman, Sachs & Co. against certain liabilities, including liabilities under the Securities Act.

       Goldman, Sachs & Co. and its affiliates have, from time to time, performed, and may in the future perform, various financial advisory and investment banking services for us and our affiliates, for which they received or will receive customary fees and expenses.

LEGAL MATTERS

       The legal validity of the notes offered hereby will be passed upon for us by Hogan & Hartson L.L.P., Baltimore, Maryland and for the underwriters by Wilmer Cutler Pickering Hale and Dorr LLP, Washington, DC.

Ciena Corporation

Convertible Senior Notes due 2013

       This prospectus relates to our Convertible Senior Notes due 2013 that we may offer and sell. The notes will be convertible into our common stock.

       The terms of the notes that are offered, and other information, will be set forth in one or more supplements to this prospectus, post-effective amendments to the registration statement of which this prospectus is a part, or in one or more documents incorporated by reference herein.

       Our common stock is traded on the Nasdaq National Market under the symbol “CIEN.”

       Investing in our securities involves risks. See “Risk Factors” contained in the accompanying prospectus supplement and in the documents incorporated herein by reference.

       Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

The date of the prospectus is April 3, 2006.

TABLE OF CONTENTS

       You should rely only on the information provided or incorporated by reference in this prospectus, any applicable prospectus supplement and any “free writing prospectus” we may authorize to be delivered to you. We have not authorized anyone to provide you with different or additional information. We are not making an offer to sell the Notes in any jurisdiction where the offer or sale of the Notes is not permitted. You should not assume that the information appearing in this prospectus, the accompanying prospectus supplement or the documents incorporated by reference herein or therein is accurate as of any date other than their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

       You should read carefully the entire prospectus, as well as the documents incorporated by reference in the prospectus and the applicable prospectus supplement, before making an investment decision.

       When used in this prospectus, except where the context otherwise requires, the terms “we,” “us” and “our” refer to Ciena Corporation.

       We have a 52 or 53 week fiscal year, which ends on the Saturday nearest to the last day of October in each year. For purposes of financial statement presentation, each fiscal year is described as having ended on October 31. Fiscal 2002, fiscal 2003, fiscal 2004 and fiscal 2005 comprised 52 weeks and fiscal 2001 comprised 53 weeks.

FORWARD-LOOKING STATEMENTS

       Some of the statements contained, or incorporated by reference, in this prospectus and the accompanying prospectus supplement discuss future expectations, contain projections of results of operations or financial condition or state other “forward-looking” information within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Those statements are subject to known and unknown risks, uncertainties and other factors that could cause the actual results to differ materially from those contemplated by the statements. The “forward-looking” information is based on various factors and was derived using numerous assumptions. In some cases, you can identify these so-called “forward-looking statements” by words like “may,” “will,” “should,” “expects,” “plans,” “anticipates,” “believes,” “estimates,” “predicts,” “potential,” or “continue” or the negative of those words and other comparable words. You should be aware that those statements only reflect our predictions. Actual events or results may differ substantially. Important factors that could cause our actual results to be materially different from the forward-looking statements are disclosed under the heading “Risk Factors” in the accompanying prospectus supplement and are disclosed in the information incorporated by reference in this prospectus, including in Item 1A, Risk Factors, page 36, of our Form 10-Q for the fiscal quarter ended January 31, 2006.

       We undertake no obligation to update or revise these forward-looking statements, whether as a result of new information, future events or otherwise.

WHERE YOU CAN FIND MORE INFORMATION

       We file annual, quarterly and current reports, proxy statements and other information with the SEC under the Securities Exchange Act of 1934. You may read and copy any reports, statements or other information on file at the SEC’s public reference room located at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the operation of the public reference room. These filings and other information that we file electronically with the SEC are available at the Internet website maintained by the SEC at http://www.sec.gov.

       We have filed with the SEC a “shelf” registration statement on Form S-3 under the Securities Act of 1933 relating to the notes that may be offered by this prospectus. This prospectus is a part of that registration statement, but does not contain all of the information in the registration statement. We have omitted parts of the registration statement in accordance with the rules and regulations of the SEC. For more detail about us and any notes that may be offered by this prospectus, you may examine the registration statement on Form S-3 and the exhibits filed with it at the location listed in the previous paragraph.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

       We incorporate information into this prospectus by reference, which means that we disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is deemed to be part of this prospectus, except to the extent superseded by information contained herein or by information contained in documents filed with the SEC after the date of this prospectus. This prospectus incorporates by reference the documents set forth below, the file number for each of which is 0-21969, that have been previously filed with the SEC (other than, in each case, documents or information deemed to have been furnished and not filed in accordance with SEC rules):

       We also incorporate by reference into this prospectus additional documents that we may file with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 from the date of this prospectus until we have sold all of the securities to which this prospectus relates or the offering is terminated. We do not incorporate by reference additional documents or information furnished to, but not filed with, the SEC.

       You may obtain copies of any of these filings through Ciena Corporation as described below, through the SEC or through the SEC’s Internet website as described above. Documents incorporated by reference are available without charge, excluding all exhibits unless an exhibit has been specifically incorporated by reference into this prospectus, by requesting them in writing, by telephone or via the Internet at:

Investor Relations

Ciena Corporation

1201 Winterson Road

Linthicum, Maryland 21090

(410) 865-8500

www.ciena.com

ir@ciena.com

       The information contained on our website does not constitute a part of this prospectus, and our website address supplied above is intended to be an inactive textual reference only and not an active hyperlink to our website.

THE COMPANY

       Ciena Corporation supplies communications networking equipment, software and services to telecommunications service providers, cable operators, governments and enterprises. We are a network specialist, with expertise in optical networking, data networking and broadband access networks. Our product and service offerings seek to enable customers to converge, transition and connect communications networks that deliver voice, video and data services. In recent years, we have expanded our product portfolio and enhanced product functionality through internal development and acquisition. We have sought to build upon our historical expertise in core optical networking by adding complementary products, software and services to support new high bandwidth applications and network convergence. This strategy has enabled us to increase penetration of our historical telecommunications customers with additional products, and to broaden our addressable markets to include participants in the cable, government and enterprise markets.

       Our principal office is located at 1201 Winterson Road, Linthicum, Maryland 21090, and our telephone number is (410) 865-8500.

USE OF PROCEEDS

       We intend to use the net proceeds from sales of the notes to provide additional funds for general corporate purposes. These purposes may include repurchases of our 3.75% Convertible Notes due February 1, 2008. These repurchases may occur at various prices from time to time.

RATIO OF EARNINGS TO FIXED CHARGES

       For the years ended October 31, 2001, 2002, 2003, 2004 and 2005, and the fiscal quarter ended January 31, 2006, earnings are inadequate to cover fixed charges and the dollar amount of coverage deficiency is disclosed in the above table, in thousands.

       These computations include us and our consolidated subsidiaries. For purposes of calculating the ratio of earnings to fixed charges, earnings consist of income (loss) before provision for income taxes, plus fixed charges. Fixed charges include interest expense on debt and the portion of rental expense under operating leases that we deem to be representative of the interest factor.

LEGAL MATTERS

       Hogan & Hartson L.L.P., Baltimore, Maryland, will provide us with an opinion as to the legal validity of the notes offered hereby.

EXPERTS

       The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended October 31, 2005 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

$300,000,000

Ciena Corporation

0.25% Convertible Senior Notes due 2013

Goldman, Sachs & Co.