Patent ID: 8364038

Claim:
A polarization multiplexed optical transmitter comprising: a first modulation unit to generate a first modulated optical signal by phase modulation and intensity modulation according to first data, the first modulation unit including a Mach-Zehnder interferometer and a first phase shifter to give a phase difference between optical paths of the Mach-Zehnder interferometer; a second modulation unit to generate a second modulated optical signal by phase modulation and intensity modulation according to second data, the second modulation unit including a Mach-Zehnder interferometer and a second phase shifter to give a phase difference between optical paths of the Mach-Zehnder interferometer; a combiner to generate a polarization multiplexed optical signal by combining the first and second modulated optical signals; a phase controller to control phase differences by the first and second phase shifters; and a signal controller to control an operation state of at least one of the first and second modulation units, wherein the phase controller controls the phase differences by the first and second phase shifters to a specified target value when the first and second data are transmitted, and controls the phase difference by the first phase shifter to the target value and the phase difference by the second phase shifter to a value shifted by an amount of π from the target value during an adjustment operation; a data pattern of the first data is same as the second data or reversed pattern of the second data during the adjustment operation; and the signal controller controls an operation state of at least one of the first and second modulation units based on an optical intensity waveform of the polarization multiplexed optical signal during the adjustment operation.