Abstract: An optical transmitter includes a signal processor and transmission circuit. The signal processor modulates a first signal to generate a first modulated signal, determines a modulo amplitude that is larger than an amplitude of the first modulated signal, inserts a second modulated signal into the first modulated signal to generate a transmission signal, corrects a symbol of the transmission signal by using an amplitude of one or a plurality of previous symbols to generate a pre-equalized signal, and performs modulo calculation based on the modulo amplitude on the pre-equalized signal. The transmission circuit generates a modulated optical signal based on an output signal of the signal processor and transmits the modulated optical signal to a reception node. An amplitude of the second modulated signal is equal to the modulo amplitude.

Abstract: An optical transmission system includes: a WDM transmission device configured to output WDM signal light including rays of a plurality of wavelengths; a wavelength converter configured to convert the WDM signal light into converted light in a different wavelength band; and a processor configured to control a signal level of the WDM signal light incident on the wavelength converter, wherein the processor controls the signal level of the WDM signal light so as to make the signal level of the WDM signal light decrease in a direction away from a wavelength of pump light used in the wavelength converter.

Abstract: A quantizer includes: a clipper configured to clip a portion exceeding a quantization range of a sample value sampled at a predetermined rate; and a noise shaper configured to determine a plurality of candidates for a quantization level based on the clipped sample value, and outputs, as a quantization value, a value obtained by adding a minimum noise in which a noise in a low-frequency region is minimum among noises generated in each candidate to the sample value before clipping.

Abstract: A phase compensation device configured to compensate phase of a received signal obtained by photoelectrically converting a phase-modulated optical signal, the phase compensation device includes a processor configured to: detect whether reversal of a phase of the received signal is present, based on a known signal contained in the received signal; compensate the phase of the received signal, based on whether reversal of the phase is detected; and after compensating the phase, compensate reversal of the phase of the received signal, based on whether reversal of the phase is detected.

Abstract: A nonlinearity compensation circuit includes a detector that detects a combination of input levels of a plurality of input signals, a memory that saves a correction value information item to compensate for nonlinear distortion, the correction value information item being saved corresponding to the combination of the input levels, and a compensator that corrects a target signal among said plurality of input signals using the correction value information item acquired from the memory based on the combination of the input levels detected by the detector.

Abstract: A quantizer includes: a clipper configured to clip a portion exceeding a quantization range of a sample value sampled at a predetermined rate; and a noise shaper configured to determine a plurality of candidates for a quantization level based on the clipped sample value, and outputs, as a quantization value, a value obtained by adding a minimum noise in which a noise in a low-frequency region is minimum among noises generated in each candidate to the sample value before clipping.

Abstract: First transmission device includes a first counter that generates counter value incremented in a specified cycle. Second transmission device includes a second counter that generates counter value incremented in the specified cycle. Polarization variation monitoring device acquires a first counter value generated by the first counter and a second counter value extracted by the first transmission device from a received frame transmitted from the second transmission device when the first transmission device detects polarization variation, and a third counter value generated by the second counter and a fourth counter value extracted by the second transmission device from a frame transmitted from the first transmission device when the second detector detects the polarization variation. The polarization variation monitoring device determines an occurrence position of the polarization variation based on the first counter value, the second counter value, the third counter value and the fourth counter value.

Abstract: First transmission device includes a first counter that generates counter value incremented in a specified cycle. Second transmission device includes a second counter that. generates counter value incremented in the specified cycle. Polarization variation monitoring device acquires a first counter value generated by the first counter and a second counter value extracted by the first transmission device from a received frame transmitted from the second transmission device when the first transmission device detects polarization variation, and a third counter value generated by the second counter and a fourth counter value extracted by the second transmission device from a frame transmitted from the first transmission. device when the second detector detects the polarization variation. The polarization variation monitoring device determines an occurrence position of the polarization variation based on the first counter value, the second counter value, the third counter value and the fourth counter value.

Abstract: A signal processing device includes: a memory; and a processor coupled to the memory and configured to: compensate an electric field signal representing an electric field component in an optical signal input from a transmission channel for an optical frequency offset between light sources on a transmission side and a reception side of the optical signal based on a compensation value; calculate an estimated value of the optical frequency offset from data having a fixed pattern in the electric field signal; generate a plurality of candidates for the compensation value from the estimated value; calculate power of the optical signal compensated for the optical frequency offset based on each of the plurality of candidates; and select an initial value of the compensation value from the plurality of candidates based on the power of the optical signal.

Abstract: An optical modulator includes: a Mach-Zehnder modulator; and a processor that controls a bias of the Mach-Zehnder modulator. The Mach-Zehnder modulator includes first and second Mach-Zehnder interferometers that are respectively formed on first and second optical paths, a phase shifter that adjusts a phase difference between the first optical path and the second optical path. The processor outputs a first bias signal for controlling an operation point of the first Mach-Zehnder interferometer, a second bias signal for controlling an operation point of the second Mach-Zehnder interferometer, and a third bias signal for controlling a phase-shift amount of the phase shifter, a low-frequency signal being superimposed on the third bias signal. The processor controls the first through third bias signals based on a frequency component of the low-frequency signal that is included in the optical signal output from the Mach-Zehnder modulator.

Abstract: An optical transmitter includes: an optical modulator including a pair of waveguides of a Mach-Zehnder interferometer to which signal light is input, and a plurality of optical phase shifters that are provided in each of the pair of waveguides and that each modulate a phase of the signal light with a plurality of drive signals; a plurality of drivers that generate the plurality of drive signals based on a plurality of digital signals corresponding to a symbol to which data signals are mapped and output the plurality of drive signals to the plurality of optical phase shifters, respectively; and a processor that shapes a waveform of the signal light such that a bandwidth of a spectrum of the signal light modulated by the optical modulator is equal to or less than a bandwidth corresponding to a rate of the symbol.

Abstract: A signal processing device includes: a memory; and a processor coupled to the memory and configured to: compensate an electric field signal representing an electric field component in an optical signal input from a transmission channel for an optical frequency offset between light sources on a transmission side and a reception side of the optical signal based on a compensation value; calculate an estimated value of the optical frequency offset from data having a fixed pattern in the electric field signal; generate a plurality of candidates for the compensation value from the estimated value; calculate power of the optical signal compensated for the optical frequency offset based on each of the plurality of candidates; and select an initial value of the compensation value from the plurality of candidates based on the power of the optical signal.

Abstract: A transmission device includes a receiver configured to receive a frame signal including synchronization data, main signal data, and an error correction code, a compensator configured to compensate for distortion of the frame signal based on a compensation coefficient, a detector configured to detect synchronization timing of the frame signal from the synchronization data; a corrector configured to correct an error of the frame signal after the distortion is compensated, based on the error correction code according to the synchronization timing, a generator configured to generate a replica signal from the frame signal after the error is corrected by the corrector, based on the synchronization timing, the replica signal corresponding to the frame signal before the distortion is compensated, and an update processor configured to update the compensation coefficient based on the replica signal and the frame signal before the distortion is compensated.

Abstract: Optical transmission device is provided in one of a plurality of nodes in an optical network. Different carrier frequencies are respectively allocated to the plurality of nodes. The optical transmission device includes: transmitter, splitter and receiver. The transmitter generates a first subcarrier optical signal with a first subcarrier established on a low-frequency side of a first carrier frequency and a second subcarrier optical signal with a second subcarrier established on a high-frequency side of the first carrier frequency. The splitter splits an optical signal including the first subcarrier optical signal and the second subcarrier optical signal. The output of the splitter is guided to first and second adjacent nodes. The receiver recovers data carried by the first subcarrier and data carried by the second subcarrier from received optical signal. A difference between carrier frequencies of adjacent nodes corresponds to a bandwidth of the subcarrier.

Abstract: A transmission device includes an imparter configured to impart redundant data to the beginning of each of a plurality of data blocks divided from a data signal, a plurality of THP operators configured to parallelly precode the plurality of data blocks to which the redundant data is imparted, a transmitter configured to sequentially transmit the plurality of data blocks precoded by the plurality of THP operators and the redundant data imparted to each of the plurality of data blocks to a transmission line according to an arrangement order in the data signal, wherein the plurality of THP operators feed back a plurality of pieces of the redundant data to the plurality of data blocks, respectively.

Abstract: Optical transmission device is provided in one of a plurality of nodes in an optical network. Different carrier frequencies are respectively allocated to the plurality of nodes. The optical transmission device includes: transmitter, splitter and receiver. The transmitter generates a first subcarrier optical signal with a first subcarrier established on a low-frequency side of a first carrier frequency and a second subcarrier optical signal with a second subcarrier established on a high-frequency side of the first carrier frequency. The splitter splits an optical signal including the first subcarrier optical signal and the second subcarrier optical signal. The output of the splitter is guided to first and second adjacent nodes. The receiver recovers data carried by the first subcarrier and data carried by the second subcarrier from received optical signal. A difference between carrier frequencies of adjacent nodes corresponds to a bandwidth of the subcarrier.

Abstract: An adaptive equalizer includes a sample buffer that temporarily stores data obtained by fractional sampling at a sampling rate that is larger than one time and smaller than two times a symbol rate; and a processor coupled to the sample buffer and configured to: specify position of a training sequence in the data based on a correlation value between a first set of (f×T) samples and a second set of (f×T) samples following the first set of samples, assuming that the sampling rate is f, and a symbol length of a code pattern included in the training sequence inserted in the data is T, and calculate an initial value of a tap coefficient set to a tap of an adaptive equalization filter based on the specified training sequence, wherein the symbol length is set to be changeable so that f×T is an integer.

Abstract: An adaptive equalizer, includes a sample buffer; and a processor coupled to the sample buffer and configured to: perform an adaptive equalization on data which has been fractionally sampled at a sampling rate higher than once a symbol rate and lower than twice the symbol rate, determine an initial value of a tap coefficient of the adaptive equalizer by using a training sequence inserted in the data, shift, by a predetermined shift amount, a sample point of one pattern from among two consecutive patterns included in the training sequence, specify a position of the training sequence in the data by replacing an original sample value with a sample value at the shifted sample point, and update the initial value of the tap coefficient based on the specified training sequence.

Abstract: A transmission device includes a receiver configured to receive a frame signal including synchronization data, main signal data, and an error correction code, a compensator configured to compensate for distortion of the frame signal based on a compensation coefficient, a detector configured to detect synchronization timing of the frame signal from the synchronization data; a corrector configured to correct an error of the frame signal after the distortion is compensated, based on the error correction code according to the synchronization timing, a generator configured to generate a replica signal from the frame signal after the error is corrected by the corrector, based on the synchronization timing, the replica signal corresponding to the frame signal before the distortion is compensated, and an update processor configured to update the compensation coefficient based on the replica signal and the frame signal before the distortion is compensated.

Abstract: An optical modulator includes: a Mach-Zehnder modulator; and a processor that controls a bias of the Mach-Zehnder modulator. The Mach-Zehnder modulator includes first and second Mach-Zehnder interferometers that are respectively formed on first and second optical paths, a phase shifter that adjusts a phase difference between the first optical path and the second optical path. The processor outputs a first bias signal for controlling an operation point of the first Mach-Zehnder interferometer, a second bias signal for controlling an operation point of the second Mach-Zehnder interferometer, and a third bias signal for controlling a phase-shift amount of the phase shifter, a low-frequency signal being superimposed on the third bias signal. The processor controls the first through third bias signals based on a frequency component of the low-frequency signal that is included in the optical signal output from the Mach-Zehnder modulator.