
<PAGE>   1




                 FIRST AMENDMENT TO AGREEMENT AND PLAN OF MERGER

           THIS FIRST AMENDMENT TO AGREEMENT AND PLAN OF MERGER (this "First
Amendment") is made as of this 27th day of August, 1998 among Tellabs, Inc., a
Delaware corporation ("Parent"), White Oak Merger Corp., a Delaware corporation
and a direct wholly owned subsidiary of Parent ("Sub"), and CIENA Corporation, a
Delaware corporation (the "Company").

           Parent, Sub and the Company are parties to that certain Agreement and
Plan of Merger dated as of June 2, 1998 (the "Merger Agreement"). Except as
otherwise defined or modified herein, all capitalized terms used in this First
Amendment shall have the meanings set forth in the Merger Agreement.

           Concurrently herewith Parent and the Company are entering into an
amendment to the Stock Option Agreement in the form of the attached Exhibit A.

           In consideration of the mutual agreements contained in the Merger
Agreement and in this First Amendment and other good and valuable consideration,
the receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

SECTION 1.  AMENDMENTS TO MERGER AGREEMENT.

           A. Amendment to Section 1.5(c) of the Merger Agreement. Section
1.5(c) of the Merger Agreement is hereby amended to read in its entirety as
follows:

              "Subject to the provisions of Sections 1.8 and 1.10 hereof, each 
            share of Company Common Stock issued and outstanding immediately 
            prior to the Effective Time (other than shares to be cancelled in
            accordance with Section 1.5(b)), together with the associated
            Rights, shall be converted into 0.80 (such number being the
            "Exchange Ratio") validly issued, fully paid and nonassessable
            shares of Parent Common Stock. All such shares of Company Common
            Stock and the associated Rights, when so converted, shall no longer
            be outstanding and shall automatically be cancelled and retired and
            each holder of a certificate representing any such shares shall
            cease to have any rights with respect thereto, except the right to
            receive any dividends and other distributions in accordance with
            Section 1.7, certificates representing the shares of Parent Common
            Stock into which such shares are converted and any cash, without
            interest, in lieu of fractional shares to be issued or paid in
            consideration therefor upon the surrender of such certificate in
            accordance with Section 1.6."
        


            B. Amendments to Section 5.7 of the Merger Agreement.

<PAGE>   2

           (I)        Section 5.7(b) of the Merger Agreement is hereby
           amended to read in its entirety as follows:

                      (i) Notwithstanding any provision in this Agreement to the
           contrary, if this Agreement is terminated (A) by the Company or
           Parent pursuant to Section 7.1(e) and a Takeover Proposal existed
           between the date hereof and the date of the Company Stockholder
           Meeting, (B) by the Company or Parent pursuant to Section 7.1(g) or
           (C) by Parent pursuant to Section 7.1(h) (except, in the case of
           Section 7.1(h)(i), as provided in Sections 5.7(d) and 5.7(e)), then,
           in each case, the Company shall (without prejudice to any other
           rights Parent may have against the Company for breach of this
           Agreement) reimburse Parent upon demand for all reasonable
           out-of-pocket fees and expenses incurred or paid by or on behalf of
           Parent or any Affiliate (as hereinafter defined) of Parent in
           connection with this Agreement, the Stock Option Agreement and the
           transactions contemplated herein or therein, including all fees and
           expenses of counsel, investment banking firms, accountants and
           consultants; provided, however, that the Company shall not be
           obligated to make payments pursuant to this Section 5.7(b)(i) in
           excess of $10,000,000 in the aggregate. As used herein, "Affiliate"
           shall have the meaning set forth in Rule 405 under the Securities
           Act.

                        (ii)  Notwithstanding any provision in this Agreement 
            to the contrary, if this Agreement  is terminated by the Company or
            Parent pursuant to Section 7.1(f) and a Parent Takeover Proposal (as
            defined below) existed between the date hereof and the date of the
            Parent Stockholder Meeting, then Parent shall (without prejudice to
            any other rights the Company may have against Parent for breach of
            this Agreement) reimburse the Company upon demand for all reasonable
            out-out-pocket fees and expenses incurred or paid by or on behalf of
            the Company or any Affiliate of the Company in connection with this
            Agreement, the Stock Option Agreement and the transactions
            contemplated herein or therein, including all fees and expenses of
            counsel, investment banking firms, accountants and consultants;
            provided, however, that Parent shall not be obligated to make
            payments pursuant to this Section 5.7(b)(ii) in excess of
            $10,000,000 in the aggregate.  As used herein, "Parent Takeover
            Proposal" means any proposal or offer, or any expression of
            interest, by any third party relating to Parent's willingness or
            ability to receive or discuss a proposal or offer for a merger,
            consolidation or other business combination, in each case pursuant
            to which Parent is  acquired by a third party.
        
            (II)        The first paragraph of Section 5.7(c) of the Merger 
            Agreement is hereby amended to read in its entirety as follows:

                        "Notwithstanding any provision in this Agreement to the
            contrary, if (i) 

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            this Agreement is terminated by the Company or Parent pursuant to
            Section 7.1(e) and a Takeover Proposal existed between the date
            hereof and the date of the Company Stockholder Meeting and,
            concurrently with or within twelve months after any such termination
            a Third Party Acquisition Event (as defined below) occurs or the
            Company shall enter into any letter of intent, agreement in
            principle, acquisition agreement or other similar agreement with
            respect to a Third Party Acquisition Event, (ii) this Agreement is
            terminated by Parent or the Company pursuant to Section 7.1(g) or
            (iii) this Agreement is terminated by Parent pursuant to Section
            7.1(h) (except, in the case of Section 7.1(h)(i), as provided in
            Sections 5.7(d) and 5.7(e)), then, in each case, the Company shall
            (in addition to any obligation under Section 5.7(b) and without
            prejudice to any other rights that Parent may have against the
            Company for a breach of this Agreement) pay to Parent a fee (the
            "Termination Fee") of $200,000,000 in cash, such payment to be made
            promptly, but in no event later than, in the case of clause (i), the
            later to occur of such termination and such Third Party Acquisition
            Event or, in the case of clauses (ii) or (iii), such termination."

            (III)       Section 5.7(d) of the Merger Agreement is hereby amended
            to read in its entirety as follows:

                        "No payment shall be required to be made by the Company
            pursuant to Section 5.7(b)(i)(C) or 5.7(c)(iii) (in each case, with
            respect to a termination of this Agreement pursuant to Section
            7.1(h)(i)) if the following conditions are satisfied: (i) no
            Takeover Proposal existed between the date hereof and the date of
            the Company Stockholder Meeting; (ii) the event described in Section
            7.1(h)(i) causing the termination of this Agreement occurred solely
            as a result of Parent entering into a definitive written agreement
            pursuant to which (x) Parent acquires, or one of Parent's
            Subsidiaries merges with, another entity and (y) in consideration
            therefor Parent agrees to issue Parent Common Stock or other voting
            securities representing, in the aggregate, 20% or more of the then
            outstanding shares of Parent Common Stock and other Parent voting
            securities (a "Parent Acquisition Event"); and (iii) prior to the
            occurrence of the event described in Section 7.1(h)(i) causing such
            termination, (A) the Board of Directors of the Company, after due
            deliberation and in the good faith exercise of its fiduciary duties
            under applicable law (as advised by outside corporate counsel of the
            Company), determined (1) to withdraw or modify such recommendation
            solely because Parent notified the Company that it intended to enter
            into or had entered into a definitive written agreement to effect a
            Parent Acquisition Event and (2) that, solely as a result of such
            Parent Acquisition Event, the Merger was no longer in the best
            interests of the Company and its stockholders and (B) the Board of
            Directors of the Company notified Parent that it had resolved to
            withdraw or modify its recommendation in favor of the approval of
            this Agreement within five business days of the receipt of Parent's


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            notice.
            (IV)        A new Section 5.7(e) of the Merger Agreement is hereby 
            added to the Merger Agreement to read as follows:

                        "Notwithstanding any provision in this Agreement to the
            contrary, and in lieu of any payments otherwise required to be made
            by the Company pursuant to Section 5.7(b)(i)(C) or 5.7(c)(iii), if
            (i) this Agreement is terminated by Parent pursuant to Section
            7.1(h)(i) and (A) no Takeover Proposal existed between the date
            hereof and the date of the Company Stockholder Meeting, (B) the
            event described in Section 7.1(h)(i) causing the termination of this
            Agreement occurred solely as a result of the occurrence of a
            Material Adverse Effect on Parent (provided that, for purposes of
            this Section 5.7(e)(i), a Material Adverse Effect on the results of
            operations of Parent and its Subsidiaries shall only be deemed to be
            such to the extent it relates to the long-term prospects of the
            results of operations of Parent and its Subsidiaries taken as a
            whole) and (C) prior to the occurrence of the event described in
            Section 7.1(h)(i) causing the termination of this Agreement, the
            Board of Directors of the Company determined in its reasonable good
            faith judgment, on the basis of the advice of outside corporate
            counsel of the Company, that the making of its recommendation to the
            stockholders of the Company in favor of approval of this Agreement,
            or the failure to withdraw or modify such recommendation, would
            violate its fiduciary duties under applicable law solely in light of
            the Material Adverse Effect on Parent or (ii) (A) no Takeover
            Proposal existed between the date hereof and the proposed Closing
            Date, (B) all of the conditions set forth in Sections 6.1 and 6.2
            (other than Section 6.2(c)) of the Merger Agreement have been
            fulfilled and (C) the Company has elected not to consummate the
            transactions contemplated hereby on the basis of Section 6.2(c) not
            being fulfilled, then, in each case, the Company shall (without
            prejudice to any other rights that Parent may have against the
            Company for a breach of this Agreement) pay to Parent a termination
            fee of $50,000,000 in cash, such payment to be made promptly, but in
            no event later than such termination."

            (V)         A new Section 5.7(f) is hereby added to the Merger
            Agreement to read as follows:

                        "Notwithstanding any provision in this Agreement to the
            contrary, if (i) this Agreement is terminated by the Company
            pursuant to Section 7.1(i) or (ii) (A) all of the conditions set
            forth in Sections 6.1 and 6.3 (other than Section 6.3(c)) of the
            Merger Agreement have been fulfilled and (B) Parent has elected not
            to consummate the transactions contemplated hereby on the basis of
            Section 6.3(c) not being fulfilled, then, in each case, Parent shall
            (without prejudice to any other rights the Company may have against
            Parent for breach of this Agreement) pay to the Company a fee of
            $100,000,000 in cash, such 

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            payment to be made promptly, but in no event later than such
            termination."

            C.          Amendment to Section 7.1 of the Merger Agreement. New
Sections 7.1(j) and 7.1(k) are hereby added to the Merger Agreement to read as 
follows:

                        "(j)        by the Company if the Company shall have
            made the $50,000,000 payment pursuant to Section 5.7(e)(ii); or

                        (k)         by Parent if Parent shall have made the
            $100,000,000 payment pursuant to Section 5.7(f)(ii)."

SECTION 2.  REPRESENTATIONS AND WARRANTIES.

            A.          Representations and Warranties of Parent and Sub. 
Parent and Sub represent and warrant to the Company as follows:

                        (1) Authority. On or prior to the date of this First
            Amendment, the Boards of Directors of Parent and Sub have declared
            the Merger (on terms and conditions set forth in the Merger
            Agreement as amended by this First Amendment) advisable and fair to
            and in the best interest to Parent and Sub, respectively, and their
            respective stockholders, approved and adopted the Merger Agreement
            (as amended hereby) in accordance with the DGCL, and the Board of
            Directors of Parent has confirmed its resolution to recommend the
            approval by Parent's stockholders of the issuance of Parent Common
            Stock in connection with the Merger. Each of Parent and Sub has all
            requisite corporate power and authority to enter into this First
            Amendment and, subject to the approval by the stockholders of Parent
            of the Share Issuance, to consummate the transactions contemplated
            by the Merger Agreement, as amended hereby. The execution and
            delivery of this First Amendment by Parent and Sub and the
            consummation by Parent and Sub of the transactions contemplated by
            the Merger Agreement, as amended hereby, have been duly authorized
            by all necessary corporate action on the part of Parent and Sub
            subject to (x) the approval by the stockholders of Parent of the
            Share Issuance and (y) the filing of appropriate Merger documents as
            required by the DGCL. This First Amendment has been duly executed
            and delivered by Parent and Sub and (assuming the valid
            authorization, execution and delivery of this First Amendment by the
            Company and the valid and binding effect hereof on the Company)
            constitutes the valid and binding obligation of Parent and Sub,
            enforceable against each of them in accordance with its terms.

                        (2) Consents and Approvals; No Violation. Assuming that
            all consents, approvals, authorizations and other actions described
            in this Section 2.A.(2) have been obtained and all filings and
            obligations described in this Section 2.A.(2) have been made, except
            as set forth in Section 2.4 of the Parent 

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            Letter, the execution and delivery of this First Amendment does not,
            and the consummation of the transactions contemplated by the Merger
            Agreement, as amended hereby, will not, result in any violation of,
            or default (with or without notice or lapse of time, or both) under,
            or give to others a right of termination, cancellation or
            acceleration of any obligation or the loss of a material benefit
            under, or result in the creation of any lien, security interest,
            charge or encumbrance upon any of the properties or assets of Parent
            or any of its Subsidiaries under, any provision of (i) the Parent
            Charter or the Parent Bylaws or the Certificate of Incorporation or
            Bylaws of Sub, (ii) any provision of the comparable charter or
            organization documents of any of Parent's Subsidiaries, (iii) any
            loan or credit agreement, note, bond, mortgage, indenture, lease or
            other agreement, instrument, permit, concession, franchise or
            license applicable to Parent or any of its Subsidiaries or (iv) any
            judgment, order, decree, statute, law, ordinance, rule or regulation
            applicable to Parent or any of its Subsidiaries or any of their
            respective properties or assets, other than, in the case of clauses
            (ii), (iii) or (iv), any such violations, defaults, rights, liens,
            security interests, charges or encumbrances that, individually or in
            the aggregate, would not have a Material Adverse Effect on Parent,
            materially impair the ability of Parent or Sub to perform their
            respective obligations hereunder or prevent the consummation of any
            of the transactions contemplated by the Merger Agreement, as amended
            hereby. No filing or registration with, or authorization, consent or
            approval of, any Governmental Entity is required by or with respect
            to Parent or any of its Subsidiaries in connection with the
            execution and delivery of this First Amendment by Parent or Sub or
            is necessary for the consummation of the Merger and the other
            transactions contemplated by the Merger Agreement, as amended
            hereby, except for (i) in connection, or in compliance, with the
            provisions of the HSR Act, the Securities Act and the Exchange Act,
            (ii) the filing of the Certificate of Merger with the Secretary of
            State of the State of Delaware and appropriate documents with the
            relevant authorities of other states in which Parent or any of its
            Subsidiaries is qualified to do business, (iii) such filings,
            authorizations, orders and approvals as may be required to obtain
            the State Takeover Approvals, (iv) such filings as may be required
            in connection with the taxes described in Section 5.11 of the Merger
            Agreement, (v) applicable requirements, if any, of state securities
            or Blue Sky Laws and NASDAQ, (vi) as may be required under foreign
            laws and (vii) such other consents, orders, authorizations,
            registrations, declarations and filings the failure of which to be
            obtained or made would not, individually or in the aggregate, have a
            Material Adverse Effect on Parent, materially impair the ability of
            Parent or Sub to perform its obligations hereunder or prevent the
            consummation of any of the transaction contemplated by the Merger
            Agreement, as amended hereby.

                        (3) Opinion of Financial Advisor. Parent has received
            the written 

<PAGE>   7

            opinion of Goldman, Sachs & Co., dated the date hereof, to the
            effect that, as of the date hereof, the Exchange Ratio (as amended
            by this First Amendment) is fair to Parent from a financial point of
            view.

            B.          Representations and Warranties of the Company.  The 
Company represents and warranties to Parent and Sub as follows:

                        (1) Authority. On or prior to the date of this First
            Amendment, the Board of Directors of the Company has declared the
            Merger (on terms and conditions set forth in the Merger Agreement as
            amended by this First Amendment) advisable and fair to and in the
            best interest of the Company and its stockholders, approved and
            adopted this First Amendment in accordance with the DGCL, confirmed
            its approval of the Stockholder Agreements and the Stock Option
            Agreement (as amended), confirmed its resolution to recommend the
            approval and adoption of the Merger Agreement (as amended hereby) by
            the Company's stockholders and directed that the Merger Agreement
            (as amended hereby) be submitted to the Company's stockholders for
            approval and adoption. The Company has all requisite corporate power
            and authority to enter into this First Amendment and, subject to
            approval by the stockholders of the Company, to consummate the
            transactions contemplated by the Merger Agreement, as amended
            hereby. The execution and delivery of this First Amendment by the
            Company and the consummation by the Company of the transactions
            contemplated by the Merger Agreement, as amended hereby, have been
            duly authorized by all necessary corporate action on the part of the
            Company, subject, in the case of the Merger Agreement, as amended
            hereby, only to (x) the approval of the Merger Agreement, as amended
            hereby, by the stockholders of the Company and (y) the filing of
            appropriate Merger documents as required by the DGCL. This First
            Amendment has been duly executed and delivered by the Company and
            (assuming the valid authorization, execution and delivery of this
            First Amendment by Parent and Sub and the validity and binding
            effect of this First Amendment on Parent and Sub) constitutes the
            valid and binding obligation of the Company enforceable against the
            Company in accordance with its terms.

                        (2) Consents and Approvals; No Violation. Assuming that
            all consents, approvals, authorizations and other actions described
            in this Section 2.B.(2) have been obtained and all filings and
            obligations described in this Section 2.B.(2) have been made, except
            as set forth in Section 3.4 of the Company Letter, the execution and
            delivery of this First Amendment by the Company does not, and the
            consummation of the transactions contemplated by the Merger
            Agreement, as amended hereby, and compliance with the provisions of
            the Merger Agreement, as amended hereby, will not, result in any
            violation of, or default (with or without notice or lapse of time,
            or both) under, or give to others a right of termination,
            cancellation or acceleration of any obligation or

<PAGE>   8

            the loss of a material benefit under, or result in the creation of
            any lien, security interest, charge or encumbrance upon any of the
            properties or assets of the Company or any of its Subsidiaries
            under, any provision of (i) the Company Charter or the Company
            Bylaws, (ii) any provision of the comparable charter or organization
            documents of any of the Company's Subsidiaries, (iii) any loan or
            credit agreement, note, bond, mortgage, indenture, lease or other
            agreement, instrument, permit, concession, franchise or license
            applicable to the Company or any of its Subsidiaries or (iv) any
            judgment, order, decree, statute, law, ordinance, rule or regulation
            applicable to the Company or any of its Subsidiaries or any of their
            respective properties or assets, other than, in the case of clauses
            (ii), (iii) or (iv), any such violations, defaults, rights, liens,
            security interests, charges or encumbrances that, individually or in
            the aggregate, would not have a Material Adverse Effect on the
            Company or materially impair the ability of the Company to perform
            its obligations hereunder or prevent the consummation of any of the
            transactions contemplated by the Merger Agreement, as amended
            hereby. No filing or registration with, or authorization, consent or
            approval of, any Governmental Entity is required by or with respect
            to the Company or any of its Subsidiaries in connection with the
            execution and delivery of this First Amendment by the Company or is
            necessary for the consummation of the Merger and the other
            transactions contemplated by the Merger Agreement, as amended
            hereby, except for (i) in connection, or in compliance, with the
            provisions of the HSR Act, the Securities Act and the Exchange Act,
            (ii) the filing of the Certificate of Merger with the Secretary of
            State of the State of Delaware and appropriate documents with the
            relevant authorities of other states in which the Company or any of
            its Subsidiaries is qualified to do business, (iii) such filings,
            authorizations, orders and approvals as may be required to obtain
            the State Takeover Approvals, (iv) such filings as may be required
            in connection with the taxes described in Section 5.11 of the Merger
            Agreement, (v) applicable requirements, if may, of Blue Sky Laws and
            NASDAQ, (vi) as may be required under foreign laws and (vii) such
            other consents, orders, authorizations, registrations, declarations
            and filings the failure of which to be obtained or made would not,
            individually or in the aggregate, have a Material Adverse Effect on
            the Company, materially impair the ability of the Company to perform
            its obligations hereunder or prevent the consummation of any of the
            transactions contemplated by the Merger Agreement, as amended 
            hereby.
            
                        (3) Opinion of Financial Advisor. The Company has
            received the written opinion of Morgan Stanley & Co. Incorporated,
            dated the date hereof, to the effect that, as of the date hereof,
            the Exchange Ratio (as amended by this First Amendment) is fair to
            the Company's stockholders from a financial point of view, a copy of
            which opinion has been delivered to Parent.



<PAGE>   9

                        (4) State Takeover Statutes; Certain Charter Provisions.
            The Board of Directors of the Company has, to the extent such
            statutes are applicable, taken all action (including appropriate
            approvals of the Board of Directors of the Company) necessary to
            exempt Parent, its Subsidiaries and affiliates, the Merger, this
            First Amendment, the Stock Option Agreement, as amended, and the
            transactions contemplated by the Merger Agreement, as amended
            hereby, from Section 203 of the DGCL. To the Knowledge of the
            Company, no other state takeover statutes or charter or bylaw
            provisions are applicable to the Merger, this First Amendment, the
            Stock Option Agreement, as amended, and the transactions
            contemplated by the Merger Agreement, as amended hereby.

SECTION 3.  MISCELLANEOUS.

            A. The terms and provisions of the Merger Agreement, as amended
hereby, shall remain in full force and effect. All references to the Merger
Agreement contained therein shall mean the Merger Agreement, as amended hereby.

            B. This First Amendment may be executed in counterparts, all of
which shall be considered one and the same agreement, and shall become effective
when one or more counterparts have been signed by each of the parties and
delivered to the other parties.

            C. This First Amendment shall be governed by, and construed in
accordance with, the laws of the State of Delaware, regardless of the laws that
might otherwise govern under applicable principles of conflicts of laws thereof.


<PAGE>   10

            IN WITNESS WHEREOF, Parent, Sub and the Company have caused this
First Amendment to be signed by their respective officers thereunto duly
authorized all as of the date first written above.

                                     TELLABS, INC.


                                     By:   /s/ MICHAEL J. BIRCK
                                          ----------------------------
                                           Name:  Michael J. Birck
                                           Title:  President and
                                                      Chief Executive Officer


                                     WHITE OAK MERGER CORP.


                                     By:   /s/ MICHAEL J. BIRCK
                                          ----------------------------
                                           Name:  Michael J. Birck
                                           Title:  President


                                     CIENA CORPORATION


                                     By:    /s/ PATRICK H. NETTLES
                                          ----------------------------
                                           Name:  Patrick H. Nettles
                                           Title:  President and
                                                      Chief Executive Officer






