POWER OF ATTORNEY

	The undersigned hereby constitutes and appoints Russell B. Stevenson, Jr.
 and Erik Lichter, or his assignee, the undersigneds true and
lawful attorney-in-fact to:

(1)	execute for and on behalf of the undersigned Form ID, Forms 3, 4
and 5 in accordance with Section 16(a) of the Securities and
Exchange Act of 1934 and the rules thereunder;

(2)	do and perform any and all acts for an on behalf of the undersigned
which may be necessary or desirable to complete the execution of
any such Form ID, Forms 3, 4 or 5 and the timely filing of such
form with the United States Securities and Exchange Commission, the
 Nasdaq Stock Market and any other authority; and

(3)	take any other action of any type whatsoever in connection with the
foregoing which, in the opinion of such attorney-in-fact, may be of
benefit to, in the best interest of, or legally required by, the
undersigned.

The undersigned hereby grants to each such attorney-in-fact full power and
authority to do and perform all and every act and thing whatsoever
requisite, necessary and proper to be done in the exercise of any of the
rights and powers herein granted, as fully to all intents and purposes as the
undersigned might or could do if personally present, with full power of
substitution or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorney-in-facts substitute or substitutes, shall
lawfully do or cause to be done by virtue of this power of attorney and the
rights and powers herein granted.  The undersigned acknowledges that the
foregoing attorney-in-fact, in serving in such capacity at the request of the
undersigned, is not assuming any of the undersigneds responsibilities to
comply with Section 16 of the Securities Exchange Act of 1934.  This Power
of Attorney can only be revoked by delivering a signed, original 'Revocation
of Power of Attorney' to the attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed as of this 15th day of December, 2006.
					Signature

					Andrew C. Petrik