A digital receiver is configured to process a polarization multiplexed carrier from a communication network. The polarization multiplexed carrier includes a first polarization and a second polarization. The receiver includes a first lane for transporting a first input signal of the first polarization, a second lane for transporting a second input signal of the second polarization, a dynamic phase noise estimation unit disposed within the first lane and configured to determine a phase noise estimate of the first input signal, a first carrier phase recovery portion configured to remove carrier phase noise from the first polarization based on a combination of the first input signal and a function of the determined phase noise estimate, and a second carrier phase recovery portion configured to remove carrier phase noise from the second polarization based on a combination of the second input signal and the function of the determined phase noise estimate.

An optical reception device 20 includes an electric signal generation unit 200, a linear compensation unit 301, a nonlinear compensation unit 300, and a second coefficient setting unit 400. The electric signal generation unit 200 generates an electric signal based on an optical signal received over a transmission path 30. The linear compensation unit 301 performs processing for compensating for dispersion that occurs on optical signal in the transmission path 30 to the electric signal, using a first filter coefficient. The second coefficient setting unit 400 determines a second filter coefficient for compensating for a nonlinear effect that occurs on the optical signal in the transmission path 30, using an amount of dispersion that occurs in the transmission path 30. The nonlinear compensation unit 300 performs processing for compensating the electric signal for the nonlinear effect, using the second filter coefficient that is determined by the second coefficient setting unit 400.

A receiving apparatus includes a first processor configured to compensate, in a perturbation back-propagation (PBP) scheme, waveform degradation of an optical signal by traveling an optical transmission line due to a nonlinear optical effect; a memory; and a second processor coupled to the memory and the second processor configured to change a gamma coefficient to be used in the PBP scheme, measure reception quality of the optical signal for each of gamma coefficients obtained by the changing, specify a gamma coefficient in accordance with the reception quality from among the gamma coefficients obtained by the changing, and set the specified gamma coefficient as a parameter of the PBP scheme.

An optical reception apparatus includes: an optical coherent reception unit that receives a frequency-modulated optical signal whose optical intensity is approximately constant and generates an I-axis component of a reception signal and a Q-axis component of the reception signal based on the optical signal; a conversion unit that generates a digital signal of the I-axis component of the reception signal and a digital signal of the Q-axis component of the reception signal; a differential detection unit that generates a differential detection signal by controlling a delay amount of the digital signal of the I-axis component and a delay amount of the digital signal of the Q-axis component so that a distance between symbols on an IQ plane is increased and by performing differential detection on the digital signal of the I-axis component whose delay amount is controlled and on the digital signal of the Q-axis component whose delay amount is controlled; and an inter-symbol-distance measuring unit that measures a distance between the symbols based on a phase change amount of the differential detection signal and feeds the distance between the symbols back to the differential detection unit.

A method and structure for probabilistic shaping and compensation techniques in coherent optical receivers. According to an example, the present invention provides a method and structure for an implementation of distribution matcher encoders and decoders for probabilistic shaping applications. The techniques involved avoid the traditional implementations based on arithmetic coding, which requires intensive multiplication functions. Furthermore, these probabilistic shaping techniques can be used in combination with LDPC codes through reverse concatenation techniques.

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.

It is difficult to obtain a demodulated signal with high signal quality in a digital optical receiver because it is difficult to compensate for each of different types of waveform distortion by a high-performance equalization process; therefore, a digital signal processor according to an exemplary aspect of the present invention includes a fixed equalization means for performing a distortion compensation process based on a fixed equalization coefficient on an input digital signal; an adaptive equalization means for performing an adaptive distortion compensation process based on an adaptive equalization coefficient on an equalized digital signal output by the fixed equalization means; a low-speed signal generation means for generating a low-speed digital signal by intermittently extracting one of the input digital signal and the equalized digital signal; a low-speed equalization coefficient calculation means for calculating a low-speed equalization coefficient to be used for a distortion compensation process of the low-speed digital signal; and a fixed equalization coefficient calculation means for calculating the fixed equalization coefficient by using at least a predetermined coefficient out of the low-speed equalization coefficient and the predetermined coefficient.

An heterodyne apparatus and method for measuring performance parameters of a coherent optical receiver at RF frequencies is disclosed. Two coherent lights are launched into signal and LO ports of the receiver with an optical frequency offset f. One of the lights is modulated in amplitude at a test modulation frequency F. COR performance parameters are determined by comparing two frequency components of the COR output. CMRR is determined based on a strength of a direct detection spectral line at the modulation frequency relative to that of spectrally-shifted lines at (F±f). GDV information is obtained by modulating one of the lights at two phase-locked frequencies, such as F and 2F, and comparing phases of two time-domain traces corresponding to frequency components of the COR output signal at the two frequencies.

Systems, devices and techniques for receiving a signal comprising a quadrature duobinary modulated signal include performing channel equalization of the received signal using a constant multi-modulus to obtain a set of channel estimation coefficients and a stream of symbols, partitioning, based on modulus, the stream of symbols into three partitions, estimating carrier frequency based on the partitioned stream of symbols, recovering a phase of the signal using a maximum likelihood algorithm, and decoding the partitioned stream of symbols to recover data.

A device for coherent detection of data transported in an optical incoming useful signal. The device includes: a first incoming single-mode optical fibre, injecting the incoming useful signal; a second incoming single-mode optical fibre, injecting an optical signal of optical frequency substantially equal to that of the incoming useful signal, referred to as an oscillation signal, a signal mixer in which one of the signals from the first or second fibre is separated into two signals having orthogonal polarisations, and where the other one of the signals from the first or second fibre is mixed with the two separate signals, producing a mixed signal; a detector of the transported data present in the mixed signal; and an amplitude modulator configured to modulate the oscillation signal before it enters the mixer, the modulation pattern having repetitive pulses of the same interval as a symbol time of the incoming useful signal.