EXHIBIT 5.1


                              [TELLABS LETTERHEAD]

                                January 25, 2002

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549

         Re:  up to 40,916,698 shares of Common Stock,
              $.01 par value per share, of Tellabs, Inc.

Ladies and Gentlemen:

         I am Vice President and Deputy General Counsel of Tellabs Operations,
Inc., a Delaware corporation and wholly-owned subsidiary of Tellabs, Inc., a
Delaware corporation (the "Company"), and, in such capacity, I am familiar with
the proceedings to date in connection with the preparation and filing with the
Securities and Exchange Commission under the Securities Act of 1933, as amended
(the "Securities Act"), of the Company's registration statement on Form S-8 (the
"Registration Statement") relating to (i) the registration of up to 2,916,698
shares of Common Stock, $.01 par value per share, of the Company (the "New
Ocular Shares") pursuant to the terms of the Agreement and Plan of Merger dated
as of November 29, 2001 among the Company, Orbit Merger Sub, Inc., a Delaware
corporation and a wholly owned subsidiary of the Company ("Sub"), and Ocular
Networks, Inc., a Delaware corporation ("Ocular"), which provides for the merger
(the "Merger") of Sub with and into Ocular, with Ocular surviving as a wholly
owned subsidiary of the Company, and (ii) the registration of up to 38,000,000
shares of Common Stock, $.01 par value per share, of the Company (the "New
Company Shares"), reserved for issuance pursuant to the exercise of options
granted under the Tellabs, Inc. 2001 Stock Option Plan, effective as of January
24, 2001.

         Based on the foregoing, I am of the opinion that:

         1. The Company is duly incorporated and validly existing under the laws
of the State of Delaware.

         2. Each New Ocular Share that is newly issued will be legally issued,
fully paid and non-assessable when (i) the Registration Statement, as finally
amended, shall have become effective under the Securities Act and (ii) the
Merger shall have become effective under the Delaware General Corporation Law.

         3. Each New Company Share that is newly issued will be legally issued,
fully paid and non-assessable when the Registration Statement, as finally
amended, shall have become effective under the Securities Act

         The foregoing opinions are limited to the federal laws of the United
States of America and the Delaware General Corporation Law. I express no opinion
as to the application of the securities or blue sky laws of the various states
to the sale of the New Ocular Shares or the New Company Shares.

I hereby consent to the filing of this opinion as an Exhibit to the Registration
Statement and to all references to my name included in or made a part of the
Registration Statement.

                                             Very truly yours,

                                             /s/ James M. Sheehan

                                             James M. Sheehan
                                             Vice President and
                                             Deputy General Counsel
                                             Tellabs Operations, Inc.