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                                                                     Exhibit 5.1





                                 May 12, 1998



Board of Directors
CIENA Corporation
1201 Winterson Road
Linthicum, MD  21090

Gentlemen:

                This firm has acted as counsel to CIENA Corporation (the
"Company"), a Delaware corporation, in connection with its registration,
pursuant to a registration statement on Form S-8 filed on or about the date
hereof (the "Registration Statement"), of 2,500,000 shares (the "Shares") of
Common Stock, par value $.01 per share, of the Company ("Common Stock"),
issuable under the CIENA Corporation Employee Stock Purchase Plan (the "Plan").
This letter is furnished to you pursuant to the requirements of Item 601(b)(5)
of Regulation S-K, 17 C.F.R. Section 229.601(b)(5), in connection with such
registration.

                For purposes of this opinion, we have examined copies of the
following documents:


                1.      An executed copy of the Registration Statement.


                2.      A copy of the Plan, as certified by the Secretary of
                        the Company on the date hereof as being complete,
                        accurate and in effect.

                3.      The Certificate of Incorporation of the Company, as
                        amended, as certified on April 21, 1998 by the
                        Secretary of State of the State of Delaware and as
                        certified by the Secretary of the Company on the date
                        hereof as being complete, accurate and in effect.

                4.      The Amended and Restated Bylaws of the Company as
                        certified by the Secretary of the Company on the date
                        hereof as being complete, accurate and in effect.

                5.      Resolutions of the Board of Directors of the Company
                        adopted on December 23, 1997, as certified by the
                        Secretary of the Company on the
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                        date hereof as being complete, accurate and in effect,
                        relating to, among other things, approval of the Plan.

                6.      A certificate of the Secretary of the Company, dated
                        May 11, 1998, as to certain facts relating to the
                        Company.

                For purposes of rendering this opinion, we have not, except as
specifically identified above, made any independent review or investigation of
factual or other matters, including the organization, existence, good standing,
assets, business or affairs of the Company.  In our examination of the
aforesaid certificates, records and documents, we have assumed the genuineness
of all signatures, the legal capacity of all natural persons, the accuracy and
completeness of all documents submitted to us, the authenticity of all original
documents and the conformity to authentic original documents of all documents
submitted to us as copies (including telecopies).  We also have assumed the
accuracy, completeness and authenticity of the foregoing certifications (of
public officials, governmental agencies and departments and corporate officers)
and statements of fact, on which we are relying, and have made no independent
investigations thereof.   This opinion is given in the context of the
foregoing.

                This opinion is based as to matters of law solely on the
General Corporation Law of the State of Delaware, as amended, and we express no
opinion as to any other laws, statutes, regulations, or ordinances, including,
without limitation, any federal or state tax or securities laws or regulations.

                Based upon, subject to, and limited by the foregoing, we are of
the opinion that the Shares, when issued and delivered in the manner and on the
terms contemplated in the Registration Statement and the Plan (with the Company
having received the consideration therefor, the form of which is in accordance
with applicable law), will be validly issued, fully paid and non-assessable.

                We assume no obligation to advise you of any changes in the
foregoing subsequent to the delivery of this opinion.  This opinion has been
prepared solely for your use in connection with the filing of the Registration
Statement on the date of this letter, and should not be quoted in whole or in
part or otherwise be referred to, nor be filed with or furnished to any
governmental agency or other person or entity, without the prior written
consent of this firm.

                We hereby consent to the filing of this opinion as Exhibit 5.1
to the Registration Statement.  In giving this consent, we do not thereby admit
that we are an "expert" within the meaning of the Securities Act of 1933, as
amended.

                                                Very truly yours,



                                                HOGAN & HARTSON  L.L.P.





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