Patent ID: 8463138

Claim:
A multi-value optical transmitter for converting an input data series which is an input electrical signal into an optical multi-value signal and outputting the optical multi-value signal, comprising: a first D/A converter to perform D/A conversion on first modulation data set based on the input data series to generate a first multi-value signal; a second D/A converter to perform D/A conversion on second modulation data set based on the input data series to generate a second multi-value signal; a light source; a dual-electrode MZ modulator comprising: a first phase modulator to modulate light from the light source based on the first multi-value signal, and a second phase modulator to modulate the light from the light source based on the second multi-value signal, the dual-electrode MZ modulator outputting the optical multi-value signal by combining an optical signal from the first phase modulator and an optical signal from the second phase modulator; a power monitor to detect an average power of the optical multi-value signal; and a DC bias controller to control a DC bias for determining an operating point of the dual-electrode MZ modulator, to maximize the average power, the DC bias controller combining a signal detected by the power monitor with a phase-shifted dither signal, phase-shifted relative to a component of the signal detected by the power monitor, to generate the DC bias.