Optical modulator, optical transmitter, and method for controlling operating point of optical modulator

A method for controlling an operating point of an optical modulator, wherein

• the optical modulator includes a ring resonator in which input light is input to an input port, a heater that is driven by a drive signal to control a temperature of the ring resonator, a modulator that modulates the input light propagating through the ring resonator according to an applied modulation signal, the modulator being provided in the ring resonator, a first light detector that detects first light output from a drop port of the ring resonator and outputs a first detection signal indicating a detection result, and a second light detector that detects second light output from a through port of the ring resonator and outputs a second detection signal indicating a detection result, and
• the method comprises:
• monitoring an intensity ratio that is a ratio of an intensity of the first light to an intensity of the second light based on the first and second detection signals;
• and
• controlling an operating point of the ring resonator by applying the drive signal based on a monitoring result of the intensity ratio to the heater.