In a method in which a compensation coefficient calculating portion (6) calculates a compensation coefficient of a compensation portion (5) which compensates transmission characteristics of a signal, a known signal is extracted from the signal. Next, a pseudo-random number is added to the extracted known signal. Next, the compensation coefficient is calculated by comparing a true value of the known signal with the known signal to which the pseudo-random number is added.

A coherent optical reception device includes a local oscillation laser that supplies laser light, a coherent optical reception front-end unit that receives a multi-level modulated optical signal, demodulates the optical signal on the basis of the laser light, and converts a demodulated optical signal into an electrical analog signal, an analog-to-digital converter that converts the analog signal into a digital signal, a compensation unit that compensates for an influence of dispersion due to a wavelength or a polarized wave of the optical signal and recovers a carrier phase of the digital signal, a constellation distortion compensation unit that compensates for constellation distortion of the multi-level modulation included in the digital signal in which an influence of dispersion is compensated for by the compensation unit, and an error correction decoding unit that performs error correction of the digital signal in which the constellation distortion is compensated for.

In order to suppress the deterioration of receiving characteristics, even in cases where a receiving band of an optical receiver is insufficient with respect to a bit rate of a received signal, an optical receiving apparatus 10 according to the present invention comprises an optical equalizer 20 that provides a light spectrum shaping for spreading an effective band width of an inputted optical signal and an optical receiver 30 that electrically converts and receives the optical signal provided with the light spectrum shaping.

A system has a plurality of non-linear circuit stages and an intervening linear circuit stage. An input signal is provided to a first non-linear circuit stage, and from the first non-linear circuit stage, to the linear circuit stage. The first non-linear circuit stage applies a second-order distortion to the input signal and provides the resulting signal to the linear circuit stage. The resulting signal that is output from the linear circuit stage is inverted with respect to the input signal and suitably linearly processed (attenuated or amplified). This signal is then provided to a second non-linear circuit that applies a second-order distortion and outputs a signal that has an overall reduction in second-order distortion.

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.

A WDM receiver configured to apply electronic equalization processing to both dispersion-compensated and dispersion-distorted versions of the received communication signal. In an example embodiment, the receiver's DSP first generates an equalized dispersion-compensated signal corresponding to the communication signal. The DSP then performs electronic dispersion-application processing on the equalized dispersion-compensated signal to generate a dispersion-distorted version thereof. The DSP then applies decision-aided electronic equalization processing to the dispersion-distorted version of the signal, subjects the resulting equalized signal to another round of dispersion-compensation processing, and recovers the data encoded in the communication signal using the resulting dispersion-compensated signal. This chain of signal processing tends to be effective in reducing nonlinear distortions of the intra-channel type and also some effects of nonlinear inter-channel interference, which advantageously enables the WDM receiver to support a lower BER and/or a higher data-transport capacity than those achievable with conventional WDM receivers.

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 may include a receiver, a monitor, and a controller. The optical reception apparatus receives multi-carrier modulated signal light modulated by a multi-carrier modulation scheme. The multi-carrier modulation scheme is available to allocate different transmission conditions for each of a plurality of subcarriers in accordance with transmission characteristics of the subcarriers. The receiver may receive from an optical transmission line a training signal light allocated with the same transmission conditions for each of the subcarriers. The monitor may monitor the transmission characteristics of the training signal light to detect a frequency at which a dip of the transmission characteristics occurs. The controller may control, based on the frequency detected by the monitor, a dispersion compensation for the multi-carrier modulated signal light having received a dispersion from the optical transmission line.

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.

In order to suppress the deterioration of receiving characteristics, even in cases where a receiving band of an optical receiver is insufficient with respect to a bit rate of a received signal, an optical receiving apparatus 10 according to the present invention comprises an optical equalizer 20 that provides a light spectrum shaping for spreading an effective band width of an inputted optical signal and an optical receiver 30 that electrically converts and receives the optical signal provided with the light spectrum shaping.