Patent ID: 8472810

Claim:
An optical signal transmitter comprising: a first modulator to generate a first modulated optical signal, the first modulator including a pair of optical paths and a first phase shifter to give a phase difference to the pair of optical paths; a second modulator to generate a second modulated optical signal, the second modulator including a pair of optical paths and a second phase shifter to give a phase difference to the pair of optical paths; a combiner to generate a polarization multiplexed optical signal by combining the first and second modulated optical signals; a phase controller to control the phase difference by the first phase shifter to A−Δφ and control the phase difference by the second phase shifter to A+Δφ when the first and second modulators are driven by first and second control data signals respectively; and a power controller to control at least one of the first and second modulators based on an AC component of the polarization multiplexed optical signal when the first and second modulators are driven by the first and second control data signals respectively; wherein a data pattern of the first control data signal is same as the second control data signal or reversed pattern of the second control data signal; and wherein A is an optimal phase determined according to a modulation scheme of the first and second modulator at a time of data transmission, and Δφ is an arbitrary phase other than zero.