Bias control circuit and optical transmitter including the same

PROBLEM TO BE SOLVED: To achieve decrease in circuit scale and reduction in power consumption.SOLUTION: A bias control circuit 200 is configured to apply a bias voltage to a DP-QPSK modulator 100 having a child modulator 51 and an optical power monitor 11, and comprises: a D/A converter 62c which generates and applies a bias voltage having a dither signal superposed to the child modulator 51; a differential amplifier 63a which outputs a voltage signal having an amplitude corresponding to the potential difference between a reference voltage signal and a monitor electric signal; an A/D converter 61c which converts the voltage signal that the differential amplifier 63a generates into a digital signal; and a controller 65 which detects a frequency component generated with the dither signal from the digital signal output from the A/D converter 61c, generates a digital signal for bias voltage control according to intensity of the frequency component, and inputs the digital signal to the D/A converter 62c.SELECTED DRAWING: Figure 1