Abstract: A light receiving circuit includes: a filter, arranged in a downstream of an electric signal amplifier to amplify an electric signal based on a light signal, to adjust a bandwidth of an amplified electric signal; a monitor circuit to monitor a communication quality of the light signal and output a monitored value; and a control circuit to control a bandwidth of the filter based on a control value corresponding to the monitored value.

Abstract: An optical apparatus comprising: a branching unit branching an input light modulated by DQSPK format and thereby outputting a first branched light and a second branched light; a first branch and a second branch inputting the first branched light and the second branched light, respectively, the first branch and the second branch having an interferometer, a photo detector, and discriminator and demodulating I-signal and Q-signal, respectively; and an abnormality detection unit detecting an abnormality of the input light based on a synchronized detection of a first demodulated signal output from the photo detector in the first branch and a first recovered signal output from the discriminator in the first branch, and a synchronized detection of a second demodulated signal output from the photo detector in the second branch and a second recovered signal output from the discriminator in the second branch.

Abstract: A calculation processing unit controls temperature of a Peltier device based on a slope of a waveform obtained by subtracting a waveform of a B-arm monitoring signal from a waveform of an A-arm monitoring signal and a value obtained by subtracting a value B of the B-arm monitoring signal from a value A of the A-arm monitoring signal. Similarly, the calculation processing unit controls a phase of the A-arm and a phase of the B-arm. An A-arm side micro-controller controls temperature of an A-arm side heater 22 based on the value of the A-arm monitoring signal, and controls the phase of the A-arm. A B-arm side micro-controller controls temperature of a B-arm side heater based on the value B of the B-arm monitoring signal, and controls the phase of the B-arm.

Abstract: First and second delay interferometers respectively have a phase-shift element. First and second photo detectors respectively detect optical signals output from the first and second delay interferometers. First and second data recovery circuits recover data from signals detected by the first and second photo detectors, respectively. A common adjustment unit adjusts the phase-shift elements of both first and second delay interferometers in accordance with an output signal from the first photo detector and an output signal from the second data recovery circuit. An individual adjustment unit adjusts the phase-shift element of the second delay interferometer in accordance with the output signal from the first photo detector and an output signal from the second photo detector.

Abstract: An optical apparatus comprising: a branching unit branching an input light modulated by DQSPK format and thereby outputting a first branched light and a second branched light; a first branch and a second branch inputting the first branched light and the second branched light, respectively, the first branch and the second branch having an interferometer, a photo detector, and discriminator and demodulating I-signal and Q-signal, respectively; and an abnormality detection unit detecting an abnormality of the input light based on a synchronized detection of a first demodulated signal output from the photo detector in the first branch and a first recovered signal output from the discriminator in the first branch, and a synchronized detection of a second demodulated signal output from the photo detector in the second branch and a second recovered signal output from the discriminator in the second branch.

Abstract: A calculation processing unit controls temperature of a Peltier device based on a slope of a waveform obtained by subtracting a waveform of a B-arm monitoring signal from a waveform of an A-arm monitoring signal and a value obtained by subtracting a value B of the B-arm monitoring signal from a value A of the A-arm monitoring signal. Similarly, the calculation processing unit controls a phase of the A-arm and a phase of the B-arm. An A-arm side micro-controller controls temperature of an A-arm side heater 22 based on the value of the A-arm monitoring signal, and controls the phase of the A-arm. A B-arm side micro-controller controls temperature of a B-arm side heater based on the value B of the B-arm monitoring signal, and controls the phase of the B-arm.