Ruo Y Li, 34Cambridge, MA

6580531, Jun 17, 2003

Dec 30, 1999

09/475836

Eric A. Swanson - Acton MA
Ruo Ding Li - Acton MA

Sycamore Networks, Inc. - Chelmsford MA

H04B 1004

359110, 359161, 359187

A method and apparatus for in-circuit biasing of a modulated laser and bit error rate testing of an optical transmitter and/or optical receiver under the control of a test controller. The test controller is communicably coupled to an interface of a module under test, as well as to external test equipment. The test controller modifies operational parameters of the modulated laser, in order to obtain a desired output power and to obtain a predetermined extinction ratio. The operational parameters of the laser include a laser bias current, an electro-absorption modulator offset bias current and a modulation depth. The disclosed test controller also determines whether the optical transmitter and/or receiver exhibit acceptable bit error rates. The disclosed test controller uses a variable optical attenuator, in combination with an erbium-doped fiber amplifier (EDFA) to control an optical signal to noise ratio for a signal terminating at either the transmitter or the receiver of the optical transceiver under test. The system measures a number of relatively low bit error rates corresponding to a number of generated signal to noise ratios and, based upon the measured values, projects a signal to noise ratio for a relatively low bit error rate so as to avoid the long period of time necessary to perform actual testing to acquire bit error rate information at high optical signal to noise ratios.