Patent ID: 9735878
Date: 2017-08-15
CPC Classifications: H04B

Claim:
1. An optical transmitter comprising: an optical modulation unit that modulates an incident light beam; a modulation signal drive unit that inputs a modulation signal to said optical modulation unit; and a controller that controls said optical modulation unit and said modulation signal drive unit, wherein said optical modulation unit includes: a branch unit that branches a light beam incident from a light source into two light beams; two mach-zehnder optical modulators that modulate said respective two light beams based on applied bias voltages and input modulation signals; an optical phase regulator that is connected to one of said two optical modulators, and regulates a phase of the light beam incident on the one optical modulator based on an applied bias voltage; a multiplexer that multiplexes output light beams from said two optical modulators and outputs a multiplexed light; and a light intensity detector that detects intensity of the light beam output from said multiplexer, said modulation signal drive unit inputs said modulation signal to each of said two optical modulators, and said controller is a controller that searches for bias voltages to be applied to said two optical modulators in an initial state as a state where said modulation signals are not input, and determines the bias voltages, wherein the applied bias voltages are determined in a state where said modulation signal is not input to each of said two optical modulators, while keeping bias voltages applied to one optical modulator of said two optical modulators and said optical phase regulator constant, said controller determines the bias voltage applied to the other optical modulator as a first initial bias voltage such that an intensity of an output light beam from the other optical modulator of said two optical modulators becomes zero, based on the intensity of the light beam detected by said light intensity detector, and thereafter, the controller determines the bias voltage applied to the one optical modulator as a second initial bias voltage such that an intensity of an output light beam from said one optical modulator becomes zero, based on the intensity of the light beam detected by said light intensity detector, while applying said first initial bias voltage to the other optical modulator, and keeping the bias voltage applied to said optical phase regulator constant.