Abstract: An optical transmission apparatus includes a Mach-Zehnder modulator, transmission lines which transmit modulation data to the Mach-Zehnder modulator, a phase varying section which is connected to at least one of the transmission lines, and a phase synchronization loop which is connected to the phase varying section, and which applies a control voltage on which a dither signal is superimposed to the phase varying section. The phase varying section adjusts a skew between the transmission lines to remain constant, based on the control voltage on which the dither signal is superimposed.

Abstract: An optical transmitter includes a modulation unit, an optical coupler, a photodetector and a control unit. The modulation unit sets up a phase difference between first and second optical signals acquired by branching an input light. The modulation unit modulates the first and second optical signals based on first and second input data signals, respectively. The optical coupler couples the first and second optical signals to generate a phase-modulated optical signal. The photodetector generates a received signal based on the phase-modulated optical signal. The control unit superimposes a dither signal having a frequency on at least one of the first and second optical signals. The control unit performs detection on the dither signal that is included in the received signal output from the photodetector. The control unit controls the phase difference that is to be set up by the modulation unit. The control of the phase difference is made based on a result of the detection.

Abstract: An optical receiver in which a failure in a certain channel affects no other channels is provided. An optical receiver inputs DQPSK optical signals supplied from the outside into each of first and second delay interferometers and reproduces optical output from the first and second delay interferometers as binary non-return-to-zero (NRZ) signals of first and second channels by first and second An optical receiving elements. The delay time of the first and second delay interferometers is performed a feedback control by a control system independent for each of the first and second channels.

Abstract: An optical transmitter for carrying out an optical modulation based on a data signal to be transmitted, thereby generating a transmission light signal, includes an optical phase modulating section for carrying out an optical phase modulation over an output light of a light source based on a data signal, an optical pulse modulating section for carrying out an optical pulse modulation over an output light of the optical phase modulating section based on a clock signal and outputting the light as an optical transmission output, an extending section for extending a code transition time of the data signal and applying the data signal to the optical phase modulating section, and a phase control section for modulating a phase shift amount of the data signal or the clock signal with a dither signal and carrying out a synchronous detection over the optical transmission output, and controlling the phase shift amount with a synchronous detection signal.

Abstract: An optical receiver for receiving a transmission light signal which is subjected to an optical phase modulation based on a data signal to be transmitted and has a dither signal superposed thereon includes a delay interferometer to which the transmission light signal having the dither signal superposed thereon is applied and which converts the transmission light signal into a light intensity modulation signal based on a control signal, a photodetector for converting two light outputs of the delay interferometer into an electric signal, two current detecting sections for differentially detecting a photocurrent flowing to the photodetector as a detection voltage, a data clock reproducing section for outputting the data signal and a clock signal based on an output of the photodetector, two filter sections for extracting dither signal components of the differential detection voltages respectively, and a control section for determining the control signal and applying the control signal to the delay interferometer i