A performance estimation apparatus and method for a nonlinear communication system and an electronic device. The nonlinear communication system is equated with by an equivalent model including an equivalent linear model and an equivalent additive noise model, and the equivalent additive noise outputted by the equivalent additive noise model is mathematically uncorrelated to the signal inputted into the equivalent model. Performances of the nonlinear communication system of different modulation formats at different baud rates may be accurately estimated.

An optical transmission system, in which an optical transmission apparatus and an optical reception apparatus are provided, includes a coefficient determination unit configured to optimize, based on a reception signal received by the optical reception apparatus, a coefficient to be used to compensate for deterioration according to characteristics of each device configuring a transmission path between the optical transmission apparatus and the optical reception apparatus, and a device characteristic estimation unit configured to estimate the characteristics of each device by using the optimized coefficient.

A local oscillation light output unit; a phase adjustment unit; a polarization control unit; a multiplexing unit; a photoelectric conversion unit; a demodulation unit; and a control unit. The phase adjustment unit adjusts the phase of local oscillation light. The polarization control unit controls polarization rotation of an optical signal. The multiplexing unit multiplexes the local oscillation light output from the phase adjustment unit with the optical signal output from the polarization control unit. The demodulation unit performs a demodulation process based on an electric signal obtained through conversion performed by the photoelectric conversion unit. The control unit, on the basis of information about the reception status of the optical signal, controls the execution of at least one of the phase adjustment of the local oscillation light in the phase adjustment unit and the polarization rotation of the optical signal in the polarization control unit.

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 apparatus includes an optical coherent reception unit that generates an I-axis component of a reception signal and a Q-axis component of the reception signal based on an optical signal subjected to continuous phase frequency shift keying, 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, a frequency offset compensation unit that derives a phase change amount or a temporal change in the Q-axis component of the differential detection signal whose component of a frequency offset has been compensated, a clock error detection unit that detects an amount of shift of a sampling phase of the differential detection signal whose component of the frequency offset has been compensated, based on the phase change amount or the temporal change in the Q-axis component of the differential detection signal, and a reception clock generation unit that generates the clock at a frequency adjusted such that the amount of shift becomes small.

Apparatus and method for digital signal constellation transformation are provided herein. In certain configurations, an integrated circuit includes an analog front-end that converts an analog signal vector representing an optical signal into a digital signal vector, and a digital signal processing circuit that processes the digital signal vector to recover data from the optical signal. The digital signal processing circuit generates signal data representing a signal constellation of the digital signal vector. The digital signal processing circuit includes an adaptive gain equalizer that compensates the signal data for distortion of the signal constellation arising from biasing errors of optical modulators used to transmit the optical signal.

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 nonlinear compensation unit (300) includes a first compensation unit (350) and a second compensation unit (360). The first compensation unit (350) compensates for each of two polarization signals E.sub.x and E.sub.y so as to cancel a first amount of phase rotation which is the amount of phase rotation calculated based on the signal strength of the two polarization signals E.sub.x and E.sub.y. The second compensation unit (360) compensates for each of the two polarization signals E.sub.x and E.sub.y so as to cancel a second amount of phase rotation which is the amount of phase rotation calculated based on the perturbative component of the two polarization signals E.sub.x and E.sub.y. The first compensation unit (350) includes a strength calculation unit (302), a first filter unit (304), and a first phase modulation unit (306). The second compensation unit (360) includes a perturbative component calculation unit (316), a second filter unit (318), a second phase modulation unit (322), and a third phase modulation unit (330).

A digital signal processing, DSP, unit (10) for use in a coherent optical receiver for an optical communications network. The DSP unit comprises an adaptive equaliser (12) and a processing block (22). The equaliser (12) comprises input ports for receiving electrical signals, each corresponding to a different state of polarization of an optical signal received by the coherent optical receiver,and output ports,each connected to a processing branch (14). A processing branch comprises a symbol sequence estimator, SSE, (16) and a carrier phase estimator, CPE, (18) comprising an input for receiving signal taped from an output of the processing branch. An output of the CPE is connected to a phase adjuster (20) interconnecting the respective output port of the equaliser and the SSE. The processing block (22) is connected to an output of the CPE,an output of the processing branch and at least one of the output of the phase adjuster and the outputs of the equalizer.

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 two phase-locked modulation frequencies F.sub.1 and F.sub.2. COR performance parameters are determined by comparing two frequency components of the COR output. The group delay variation (GDV) information is obtained by comparing phases of two time-domain traces corresponding to frequency components of the COR output signal at the two modulation frequencies shifted by the optical frequency offset f.