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.

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.

The present disclosure provides example method for sending a signal in optical communication, an example optical transmitter, and an example optical communication system. One example method for sending a signal in optical communication includes generating, by an optical transmitter, multiple first subcarriers based on a bit stream. State of polarization (SOP) rotation is performed by the optical transmitter on at least one subcarrier in the multiple first subcarriers to generate multiple second subcarriers, wherein the multiple second subcarriers comprise multiple subcarriers each with a relative SOP rotation angle, and the relative SOP rotation angle is not zero and is not an integer multiple of 90 degrees. The multiple second subcarriers are modulated to an optical signal. The modulated optical signal is sent by the optical transmitter.

The present disclosure provides example method for sending a signal in optical communication, an example optical transmitter, and an example optical communication system. One example method for sending a signal in optical communication includes generating, by an optical transmitter, multiple first subcarriers based on a bit stream. State of polarization (SOP) rotation is performed by the optical transmitter on at least one subcarrier in the multiple first subcarriers to generate multiple second subcarriers, wherein the multiple second subcarriers comprise multiple subcarriers each with a relative SOP rotation angle, and the relative SOP rotation angle is not zero and is not an integer multiple of 90 degrees. The multiple second subcarriers are modulated to an optical signal. The modulated optical signal is sent by the optical transmitter.

Embodiments of the present invention provide a receiver and a data receiving method. The receiver includes: two first input ends, configured to receive a digital signal of an X-polarization state and a digital signal of a Y-polarization state; a despreading module, configured to despread the digital signal of the X-polarization state and the digital signal of the Y-polarization state based on N delay values and spreading codes of N transmitters, to obtain N first baseband signals and N second baseband signals; and a multiple-input multiple-output equalization module, configured to perform equalization filtering processing on the N first baseband signals and the N second baseband signals, to obtain recovered data of the first polarization states and recovered data of the second polarization states of the N transmitters. In the embodiments of the present invention, the coherent CDMA multipoint-to-point data transmission in an optical communications system is implemented.

Embodiments of the present invention provide a receiver and a data receiving method. The receiver includes: two first input ends, configured to receive a digital signal of an X-polarization state and a digital signal of a Y-polarization state; a despreading module, configured to despread the digital signal of the X-polarization state and the digital signal of the Y-polarization state based on N delay values and spreading codes of N transmitters, to obtain N first baseband signals and N second baseband signals; and a multiple-input multiple-output equalization module, configured to perform equalization filtering processing on the N first baseband signals and the N second baseband signals, to obtain recovered data of the first polarization states and recovered data of the second polarization states of the N transmitters. In the embodiments of the present invention, the coherent CDMA multipoint-to-point data transmission in an optical communications system is implemented.

According to a signal transmitting method, a signal receiving method, and a related device and system, a generated single-wavelength optical carrier may be split into N subcarriers with a same wavelength by using a splitting device, corresponding data modulation and corresponding amplitude spread spectrum modulation are performed on the N subcarriers by using N spreading codes and N low-speed data signals obtained by deserializing a received high-speed data signal, to obtain N spread spectrum modulation signals, and the N spread spectrum modulation signals are combined and output. A multicarrier generation apparatus or the like having a relatively complex structure does not need to be used for optical carrier splitting, and spectrum spreading does not need to be performed in a phase modulation manner in which a plurality of delay units or controllable phase units are required.

Systems and methods for operating an optical modem include operating with first operating settings; and, responsive to detection or expectation of a disturbance in an operating condition associated with the optical modem, operating with second operating settings for a time period based on statistical properties of the disturbance. The systems and methods can further include reverting to the first operating settings after the time period. The disturbance can be a polarization transient or a transient affecting a laser or a clock. The second operating settings can cause a reduced margin relative to the first operating settings for the time period.

The present invention relates to signal processing in an optical receiver, in particular to equalization performed in coherent optical receivers. A multiple-input multiple-output (MIMO) equalizer receives and equalizes a plurality of real value signals, for example four sampled electrical baseband tributaries (HI, HQ, VI, VQ). The outputs of the multiple-input multiple-output (MIMO) equalizer provide equalized real or imaginary components of complex signals. The complex signals including the real and imaginary components are then each and individually equalized to remove chromatic dispersion.

A tap-coefficient control circuit sets the tap coefficient converged by the second tap coefficient updater as an initial value of the tap coefficient in the first digital filter which is to be updated by the first tap coefficient updater, arranges the tap coefficients converged by the second tap coefficient updater in descending order of contribution degree to the convergence operation of tap coefficient update in the first tap coefficient updater, judges the tap coefficient not less than upper specified number to be valid and the tap coefficient less than the specified number to be invalid, and sets the tap coefficient of the first digital filter corresponding to the tap coefficient judged to be invalid to zero not to be used in a calculation of the first tap coefficient updater until a next judgment result is made.