An optical device includes a light source and diffuser, such as non-linear material, to form a supercontinuum of light energy of different wavelengths. An optical channel generator forms channels from the supercontinuum and forwards a multiplexed signal carrying the channels. The signal travels to an optical receiver through an optical fiber. The optical receiver identifies a non-linear penalty associated with forwarding the multiplexed signal on the optical fiber. The optical receiver modifies attributes of the received channels, such as increasing the magnitude of one of the channels, to cancel out the non-linear penalty.

An adaptive equalizer with coefficients determined by averaging an estimated filter coefficient over a number, N, of past and future symbols. Estimated filter coefficients may be optimized by optimization of the number N, an averaging window function and a scaling factor using a metric. The metric also allows estimation of the amount of noise that may be compensated by an adaptive equalizer consistent with the present disclosure.

Techniques for receiving a modulated optical signal which has undergone a digital Fourier transform spreading (DFTS), include generating digital samples of the modulated optical signal, performing resampling and synchronization of the digital samples to generate time-corrected digital samples from an input wireless signal, compensating the time-corrected digital samples for nonlinearity (NL) to produce NL-compensated digital samples, de-spreading the NL-compensated digital samples using an inverse digital Fourier transform to recover quadrature amplitude modulation (QAM) modulated signals, applying post-equalization to the QAM signals to generate equalized QAM signals, performing a decision directed least mean square (DD-LMS) equalization to generate blind-optimized QAM signals and demodulating the blind-optimized QAM signals to recover data bits.

A method of optical communication, implemented at a receiver in an optical communication network, includes receiving an optical signal carrying modulated information bits, processing the optical signal through a receiver subsystem to generate a stream of digitized modulation symbols from the optical signal, and producing, using the digitized modulation symbols as input symbols to an iterative process, estimates of information bits. Each iteration includes: generating estimated output symbols from input symbols by filtering by an estimate of inverse of the optical channel, updating, using the estimated output symbols, the estimate of the inverse of the optical channel to minimize a measure of error, and compensating the estimated output symbols by using pre-distortion values from a look-up table (LUT) to generate compensated output symbols that are used as input to a next iteration.

An optical receiver may include a digital signal processor to receive an input sample that includes transmitted data, transmitted by an optical transmitter, and nonlinear distortion. The digital signal processor may process the input sample to generate an estimated data value. The estimated data value may be an estimate of the transmitted data. The digital signal processor may remove the estimated data value from the input sample to generate a noise sample. The digital signal processor may determine a nonlinear distortion value based on the input sample, the estimated data value, and the noise sample. The nonlinear distortion value may be an estimate of the nonlinear distortion included in the input sample. The digital signal processor may remove the nonlinear distortion value from the input sample to generate an output sample, and may output the output sample.

A non-linear distortion compensator includes: a first signal generator configured to generate a signal with a second multivalued level lower than a first multivalued level from an input signal; a non-linear distortion calculator configured to calculate non-linear distortion of the signal with the first multivalued level based on the signal with the second multivalued level generated by the first signal generator; and a non-linear compensator configured to compensate the non-linear distortion of the signal with the first multivalued level based on the non-linear distortion calculated by the non-linear distortion calculator.

An adaptive equalizer with coefficients determined by averaging an estimated filter coefficient over a number, N, of past and future symbols. Estimated filter coefficients may be optimized by optimization of the number N, an averaging window function and a scaling factor using a metric. The metric also allows estimation of the amount of noise that may be compensated by an adaptive equalizer consistent with the present disclosure.

Embodiments of the present disclosure provide an estimation apparatus and method for nonlinear distortion and a receiver. The estimation method for nonlinear distortion includes: sampling a band-limited analog signal to obtain a sampling sequence; calculating a nonlinear perturbation coefficient in nonlinear distortion estimation based on a Nyquist pulse; calculating a nonlinear perturbation term superimposed on a signal by using the nonlinear perturbation coefficient and the sampling sequence; and calculating a nonlinear distortion waveform by using the nonlinear perturbation term. With the embodiments of the present disclosure, not only any modulation formats are compatible, but also advantages of high precision and good adaptability may be achieved.

A signal reception processing apparatus includes a digital signal processing unit that calculates a first Q value based on distribution of the symbols of the demodulated signal and distance between the symbols of the demodulated signal, and an error correction unit that outputs corrected signal as a demodulation electric signal, and calculates a second Q value based on an error rate at the time of the correction, and a control unit that calculates a penalty that indicates degradation quantity of signal quality caused by a nonlinear optical effect of an optical fiber based on the first Q value and the second Q value.

An optical receiver includes a dividing unit, a control unit, and a compensating unit. The dividing unit divides an optical transmission signal into a plurality of frequency components by a set number of divisions and a set division bandwidth. The control unit controls the number of divisions and the division bandwidth on the basis of transmission path information about an optical transmission line through which the optical transmission signal is transmitted and signal information about the optical transmission signal. The compensating unit compensates optical nonlinear distortion of each of the frequency components divided by the dividing unit.