An optical reception device includes a coefficient update section which optimizes a dispersion coefficient used in compensation of wavelength dispersion of a received signal obtained by receiving an optical signal according to a coherent detection method and a phase rotation amount used in compensation of a nonlinear optical effect of the received signal, and a transmission characteristic estimation section which estimates a transmission characteristic of a transmission line by using the optimized dispersion coefficient and the optimized phase rotation amount.

A detector coherent-receives a signal being transmitted from a transmitter. A filter group includes a plurality of filters connected in series along a signal path of a reception signal. The plurality of filters include a plurality of non-linear distortion compensation filters and one or more linear distortion compensation filters. A coefficient updating unit controls a filter coefficient of the plurality of non-linear distortion compensation filters and a filter coefficient of at least some of the linear distortion compensation filters. The coefficient updating unit adaptively controls the filter coefficient, by using an error back propagation method, based on a difference between an output signal being output from the filter group and a predetermined value of the output signal.

An optical reception device includes a nonlinear optical compensation section which performs compensation of wavelength dispersion of a received signal obtained by receiving an optical signal according to a coherent detection method and compensation of a nonlinear optical effect of the received signal N (N is an integer of at least 1) step(s), and a coefficient update section which updates a coefficient so as to optimize the coefficient used in each step of the nonlinear optical compensation section based on a signal having been subjected to the compensation by the nonlinear optical compensation section and a predetermined training signal.

A coherent receiver includes a receive signal path including i) an input configured to connect a receive signal, ii) one or more signal paths connected to the input and to one or more optical hybrids, and iii) a variable optical attenuator (VOA) in each of the one or more signal paths; and a local oscillator (LO) signal path including i) an input configured to connect to an LO and the one or more optical hybrids, and ii) one or more complementary VOAs located between the input and the one or more optical hybrids, wherein the one or more complementary VOAs are configured to cancel any phase changes from the VOA in each of the one or more signal paths. The VOA in each of the one or more signal paths and the one or more complementary VOAs can be p-i-n junctions.

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.

The invention provides a method for nonlinear compensation of coherent high-capacity high-order QAM system, including: deploying an OPC on an intermediate link of communication between a transmitter and receiver, and performing phase conjugation on a transmitted signal based on the OPC to generate idler; performing phase recovery on a compensated signal at the receiver to obtain a constellation diagram, simulating a nonlinear function relationship between a transmitted signal and a received signal by using a trained and learned CVDNN, and performing nonlinear compensation on the constellation diagram to obtain the compensated constellation diagram; and calculating a Q-factor based on the compensated constellation diagram, and evaluating communication performance by the Q-factor. Nonlinear compensation is performed on a transmitted signal by using an OPC+CVDNN method to equalize nonlinear degradation of an optical fiber in a WDM coherent optical communication system.

An apparatus and method to measure nonlinear system noises may include a processor to generate a bilateral notch signal, a unilateral notch signal and a multi-tone signal; to measure power of an additive Gaussian white noise of a nonlinear system by using the multi-tone signal; to measure a first power-to-noise ratio of the nonlinear system by using the bilateral notch signal; to measure a second power-to-noise ratio of the nonlinear system by using the unilateral notch signal. The processor is to calculate a nonlinear power-to-noise ratio of the nonlinear system and a power-to-noise ratio introduced by IQ imbalance according to the power of the additive Gaussian white noise, the first power-to-noise ratio and the second power-to-noise ratio.

A system and method for mitigating nonlinearity in an optical communication link with multiple carriers uses mutual frequency referencing to stabilize at least a portion of the multiple carriers. Using at least one frequency-referenced signal, carrier nonlinearity can be determined and compensated within the link by pre-distortion, back-propagation, or a combination of both. Mutual frequency referencing may be performed at the emitting end of the link, at the receiving end, or a combination of both.

An optical transmission system according to an embodiment includes: an optical transmission unit which modulates an optical signal into which a known signal is inserted and transmits the optical signal; and an optical reception unit which receives the optical signal from the optical transmission unit, wherein the optical reception unit includes: an optical receiver which performs coherent detection of a reception signal of the optical signal received from the optical transmission unit; a receiver transfer function estimation section which estimates a nonlinear response transfer function of the optical receiver based on the known signal included in the reception signal after the detection by the optical receiver; and a receiver compensation section which compensates nonlinear distortion of the reception signal after the detection based on the nonlinear response transfer function which the receiver transfer function estimation section estimates.

An optical receiving device that divides receive signals obtained by receiving an optical signal using a coherent detection scheme into a plurality of frequency bands, matches timing of the receive signals along a time axis between the frequency bands resulting from the division, performs a combining process of combining the receive signals contained in the plurality of frequency bands, and compensates the receive signals for waveform distortion either before or after the combining process, includes: a first wavelength dispersion compensation unit adapted to compensate the receive signals for waveform distortion in each of the frequency bands resulting from the division; a first nonlinear compensation unit adapted to compensate the receive signals belonging to each of the frequency bands and timed with each other in a time domain for a nonlinear optical effect; and a second wavelength dispersion compensation unit adapted to compensate the receive signals belonging to each of the frequency bands and compensated for the nonlinear optical effect for wavelength dispersion in each of the frequency bands.