Patent ID: 9007675
Filing Date: 2015-04-14
Classification: G02F,H04B

Abstract:
1. An optical modulation device comprising: a first modulation unit that includes: a first modulator that forms a first optical modulation signal by modulating a light based on a first drive signal and a first bias signal; a second modulator that forms a second optical modulation signal by modulating a light based on a second drive signal and a second bias signal; and a phase shifter that makes a phase difference between the first optical modulation signal and the second optical modulation signal closer to π/2 by shifting a phase of the first optical modulation signal with respect to the second optical modulation signal based on a third bias signal, the first drive signal and the second drive signal being superimposed over a first pilot having a first frequency, the first bias signal and the second bias signal being superimposed over a second pilot having a second frequency, the third bias signal being superimposed over a third pilot; a detection unit that detects the first pilot, the second pilot, and the third pilot included in a synthesized signal synthesizing the first optical modulation signal phase-shifted in the phase shifter and the second optical modulation signal; and a controller that repeatedly adjusts a signal as a target of adjustment in each of a plurality of adjustment periods, wherein the controller adjusts the third bias signal based on a detection result for the third pilot in a first adjustment period, adjusts the first drive signal and the first bias signal based on a detection result for the first pilot and a detection result for the second pilot in a second adjustment period next to the first adjustment period, and adjusts the second drive signal and the second bias signal based on the detection result for the first pilot and the detection result for the second pilot in a third adjustment period next to the second adjustment period, wherein the controller controls a length of the first adjustment period to be equal to or greater than one cycle of the third pilot and equal to or less than a time constant at the time of adjustment of the third bias signal, controls a length of the second adjustment period to be equal to or greater than one cycle of the first pilot and equal to or less than a time constant at the time of adjustment of the first drive signal and the first bias signal, and controls a length of the third adjustment period to be equal to or greater than one cycle of the second pilot and equal to or less than a time constant at the time of adjustment of the second drive signal and the second bias signal.