OPTICAL TRANSMITTER, AND BIAS CONTROL METHOD OF LIGHT MODULATOR

摘要

PROBLEM TO BE SOLVED: To provide a technique capable of stably controlling a bias voltage of a light modulator to an optimal point irrespective of a driving amplitude of the light modulator.SOLUTION: An optical transmitter includes: a light modulator including a pair of Mach-Zehnder type modulators and a phase shift unit that applies a predetermined phase difference between the pair of Mach-Zehnder type modulators; a pair of modulator drivers that drives the light modulators; a low-frequency generator that produces a low-frequency signal which varies the ratio of a half-wavelength voltage of each of the light modulators to a driving amplitude; a photo-detection unit that detects part of an output of each of the light modulators; a wave detection unit that uses the low-frequency signal to detect a low-frequency component contained in an output of the photo-detection unit; and a bias voltage control unit that controls a bias voltage of each of the light modulators so that the low-frequency component to be detected becomes in phase with the low-frequency signal and becomes maximum.SELECTED DRAWING: Figure 7