METHOD AND CIRCUIT FOR COMPENSATING FOR DISTORTION OF OPTICAL MODULATOR

摘要

PROBLEM TO BE SOLVED: To simplify a distortion compensating circuit requiring a complex configuration for generating negative-phase distortion. SOLUTION: This distortion compensating circuit 31 is connected in series with an input route of an optical modulator/demodulator system 22 or an output route, and generates a distortion for offsetting a distortion caused by a non- linear characteristic of an optical modulator 23 in the optical modulator/ demodulator system 22. The optical modulator 23 is an electro-absorption optical modulator, and the distortion compensating circuit 31 is used under the condition that a bias voltage to be applied to the electro-absorption optical modulator is set to a voltage value by which the phase of the distortion generated by the electro-absorption optical modulator is shifted by 180 deg.. The distortion compensating circuit 31 comprises an amplifier 32 generating distortion and a variable attenuator 6 for adjusting attenuation of the distortion generated from the amplifier 32, and offsets the distortion generated in the optical modulator 23 by adjusting the attenuation of the distortion generated from the amplifier 32 by the variable attenuator 6.