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                                                                     EXHIBIT 8.1



                    [GIBSON, DUNN & CRUTCHER LLP LETTERHEAD]



                                  June 5, 2000


(213) 229-7000                                                     C 41507-00001


Harmonic Inc.
549 Baltic Way
Sunnyvale, California 94089

     Re:  Acquisition of C-Cube Microsystems Inc.

Ladies and Gentlemen:

     We have acted as counsel to Harmonic Inc., a Delaware corporation
("HARMONIC"), in connection with the preparation and execution of the Amended
and Restated Agreement and Plan of Merger and Reorganization (the "MERGER
AGREEMENT"), dated as of December 9, 1999, by and between Harmonic and C-Cube
Microsystems Inc., a Delaware corporation ("C-CUBE"). Pursuant to the Merger
Agreement, C-Cube has merged with and into Harmonic, with Harmonic surviving the
merger (the "MERGER"). The Merger and certain proposed transactions incident
thereto are described in the Registration Statement on Form S-4 (the
"REGISTRATION STATEMENT") of Harmonic, which includes the Joint Proxy
Statement/Prospectus/Information Statement (the "JOINT PROXY STATEMENT") of
C-Cube and Harmonic, that was filed with the Securities and Exchange Commission
under the Securities Act of 1933 and which became effective on March 24, 2000.

     You have requested our opinion regarding certain federal income tax
consequences of the Merger. In rendering this opinion, we have assumed and
relied upon (without any independent investigation):

     1.   The truth and accuracy of the statements, covenants, representations
and warranties contained (a) in the Merger Agreement, (b) in the representations
received from Harmonic and C-Cube (the "TAX REPRESENTATION LETTERS") that have
been provided to us and dated as of May 3, 2000, and (c) in the Registration
Statement;
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Harmonic Inc.
June 5, 2000
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     2.   that the Merger was consummated in accordance with the Merger
Agreement, without any waiver, breach or amendment of any material provisions of
the Merger Agreement, the effectiveness of the Merger under applicable state
law, and the performance of all covenants contained in the Merger Agreement and
the Tax Representation Letters without waiver or breach of any material
provisions thereof, in each case except as otherwise provided in the Waiver
Agreement entered into between Harmonic and C-Cube as of April 21, 2000;

     3.   the accuracy of any representation or statement made "to the knowledge
of" or similarly qualified without such qualification, and as to all matters in
which a person or entity is making a representation, that such person or entity
is not a party to, does not have, and is not aware of, any plan, intention,
understanding or agreement inconsistent with such representation, and there is
no such plan, intention, understanding, or agreement inconsistent with such
representation;

     4.   the reporting of the Merger as a reorganization, within the meaning of
Section 368(a) of the Internal Revenue Code of 1986, as amended (the "CODE"), by
Harmonic and C-Cube in their federal income tax returns;

     5.   the authenticity of original documents (including signatures),
conformity to the originals of documents submitted to us as copies, and due
execution and delivery of all documents where due execution and delivery are
prerequisites to effectiveness thereof; and

     6.   the absence of any occurrence since the date of the Tax Representation
Letters that could have caused any of the declarations and representations
contained in those letters to be untrue, incorrect, or incomplete in any respect
at any time since such date.

     Based upon the foregoing, the discussion contained in the Joint Proxy
Statement under the caption "Material Federal Income Tax Consequences of the
Merger," subject to the limitations and qualifications described therein and
herein, and as of March 24, 2000, is our opinion with respect to the federal
income tax consequences generally applicable to the Merger.

     This opinion represents our best judgment regarding the application of
federal income tax laws under the Code, existing judicial decisions,
administrative regulations and published rulings and procedures. Our opinion is
not binding upon the Internal Revenue Service or the courts, and there is no
assurance that the Internal Revenue Service will not successfully assert a
contrary position. Furthermore, no assurance can be given that future
legislative, judicial or administrative changes, on either a prospective or
retroactive basis, would not adversely affect the accuracy of the conclusions
stated herein. We undertake no responsibility to advise you of any new
developments in the application or interpretation of the federal income tax
laws. Furthermore, in the event any one of the statements, covenants,
representations, warranties or assumptions upon which we have relied to issue
this opinion is incorrect, our opinion might be adversely affected and may not
be relied upon.
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Harmonic Inc.
June 5, 2000
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     This opinion addresses only the matters described above, and does not
address any other federal, state, local or foreign tax consequences that may
result from the Merger or any other transaction (including any transaction
undertaken in connection with the Merger).

     This opinion may not be relied upon for any other purpose or by any other
person or entity, and may not be furnished to, quoted to or by or relied upon by
any other person or entity, without our prior written consent.

                                       Very truly yours,


                                       /s/ GIBSON, DUNN & CRUTCHER LLP
                                       -------------------------------
                                       Gibson, Dunn & Crutcher LLP