System and method for controlling a difference in optical phase and an optical signal transmitter

An optical signal transmitter comprising:

• a plurality of modulators for receiving a plurality of optical short-pulse trains and encoding the plurality of optical short-pulse trains to output a plurality of modulated optical signals;
• an interferometer for receiving part of a single optical time-division multiplexed signal, obtained by multiplexing the plurality of modulated optical signals encoded by said modulators, to split it into first and second signals, and giving, between the first and second signals, a phase difference equivalent to one bit of the optical time-division multiplexed signal, and thereafter multiplexing the first and second signals;
• a low-frequency extractor for adding together signals, output from said interferometer, which have similar intensity every two successive bits, and extracting a low-frequency waveform signal as a signal for controlling the phase difference of the single optical time-division multiplexed signal;
• and
• a controller connected to said modulators and said interferometer for adjusting said modulators so that the signal extracted by said low-frequency extractor has a maximum value.

An optical signal transmitter comprising:

• a plurality of modulators for receiving a plurality of optical short-pulse trains and encoding the plurality of optical short-pulse trains to output a plurality of modulated optical signals;
• a first interferometer for receiving part of a single optical time-division multiplexed transmission signal, obtained by multiplexing the plurality of modulated optical signals encoded by said modulators, to split it into first and second signals, and giving, between the first and second signals, a phase difference equivalent to one bit of the optical time-division multiplexed signal, and thereafter multiplexing the first and second signals;
• a low-frequency extractor for adding together signals, output from the first interferometer, which have similar intensity every two successive bits, and extracting a low-frequency waveform signal as a signal for controlling the phase difference of the single optical time-division multiplexed signal;
• a second interferometer for receiving one of two optical time-division multiplexed transmission signals being under multiplexing, obtained by multiplexing the plurality of modulated optical signals, to split it into third and fourth signals, and giving, between the third and fourth signals, a phase difference equivalent to one bit of the one optical time-division multiplexed signal, and thereafter multiplexing the third and fourth signals;
• a third interferometer for receiving another of the two optical time-division multiplexed transmission signals to split it into fifth and sixth signals, and giving, between the fifth and sixth signals, a phase difference equivalent to one bit of the other optical time-division multiplexed signal, and thereafter multiplexing the fifth and sixth signals;
• and
• a controller connected to said modulators and said first, second and third interferometers for receiving the optical time-division multiplexed signals from said second and third interferometers, and adjusting said modulators so that an optical phase difference in the two optical time-division multiplexed signals is zero, and for adjusting said modulators so that the signal extracted by the low-frequency extractor has a maximum value.