Methods and systems for low complexity interference cancellation in multichannel optical transmission. Local or self-iteration is performed one or more times between an expected propagation decision feedback equalizer and a soft demapper. Following local iteration, a soft decision forward error correction decoder determines bit log-likelihood ratios, which are fed back to the expected propagation decision feedback equalizer and soft demapper for further self-iteration. Global iteration involving the decoder can also be performed one or more times before a bitstream is decoded.

A polarization scrambler using a retardance element (RE) is disclosed. The polarization scrambler may include an optical fiber input to transmit an optical signal, and a beam expander to receive and expand the optical signal to create an expanded optical signal. The polarization scrambler may include a retardance element (RE) to cause a polarization scrambling effect on the expanded optical signal and to create a scrambled expanded optical signal. The polarization scrambler may include a beam reducer to receive and reduce the scrambled expanded optical signal to create a scrambled optical signal. The polarization scrambler may include an optical fiber output to receive scrambled optical signal. The optical fiber output may transmit the scrambled optical signal to one or more downstream optical components.

A polarization scrambler using a retardance element (RE) is disclosed. The polarization scrambler may include an optical fiber input to transmit an optical signal, and a beam expander to receive and expand the optical signal to create an expanded optical signal. The polarization scrambler may include a retardance element (RE) to cause a polarization scrambling effect on the expanded optical signal and to create a scrambled expanded optical signal. The polarization scrambler may include a beam reducer to receive and reduce the scrambled expanded optical signal to create a scrambled optical signal. The polarization scrambler may include an optical fiber output to receive scrambled optical signal. The optical fiber output may transmit the scrambled optical signal to one or more downstream optical components.

An optical Digital Signal Processor (DSP) circuit includes a digital core configured to implement digital signal processing functionality and configured to operate at a plurality of baud rates including a full baud rate and a half-baud rate; and an analog interface including a Digital-to-Analog Converter (DAC) section and an Analog-to-Digital Converter (ADC) section, wherein the analog interface is connected to the digital core and is configured to operate at the full baud rate when the digital core is configured to operate at any of the plurality of baud rates.

An optical Digital Signal Processor (DSP) circuit includes a digital core configured to implement digital signal processing functionality and configured to operate at a plurality of baud rates including a full baud rate and a half-baud rate; and an analog interface including a Digital-to-Analog Converter (DAC) section and an Analog-to-Digital Converter (ADC) section, wherein the analog interface is connected to the digital core and is configured to operate at the full baud rate when the digital core is configured to operate at any of the plurality of baud rates.

An object of the present invention is to provide an optical transmission system capable of controlling a transmission capacity and a signal processing load of a MIMO equalizer, without depending on the number of propagation modes of the optical fiber. The present optical transmission system includes an optical fiber 11 with the number of spatial modes being L (an integer of 2 or greater), an optical multiplexer 13 connected to one end of the optical fiber 11 and configured to input M (a natural number of L or less) signal beams of light to the optical fiber 11 and cause the M input signal beams of light to be propagated for each of the spatial modes of the optical fiber 11, an optical demultiplexer 14 connected to another end of the optical fiber 11 and configured to demultiplex a propagated beam of light propagated through the optical fiber 11 for each of the spatial modes of the optical fiber 11, N (N=L) receivers 15 configured to each receive a demultiplexed beam of light obtained by demultiplexing the propagated beam of light, a signal generation apparatus 17 configured to generate P (an integer of from M to L) combined signals from the N received signals, and a P×M MIMO equalizer 16 configured to receive the P combined signals to output M demodulated signals.

A tentative decision is made for symbols on the basis of a received signal and a decision threshold, and a tentative decision signal including a sequence of the symbols is output. A scale value indicating a rate of increase or reduction of the received signal or a threshold change rate indicating a degree of change in the decision threshold is updated so that an appearance frequency of each of symbols included in the tentative decision signal matches an appearance frequency of each of symbols in a reference signal obtained by modulating a transmitted signal with a modulation method used in transmission which is shared between a transmitting side and a receiving side, and an SN ratio is calculated using the scale value or the threshold change rate when a degree of agreement between the appearance frequencies is within a predetermined permissible range. When the scale value is updated, a tentative decision is made for the symbols on the basis of the received signal increased or reduced by the updated scale value and the decision threshold, and when the threshold change rate is updated, the tentative decision for the symbols is made on the basis of the received signal and the decision threshold to which the updated threshold change rate is applied.

Methods and systems for low complexity interference cancellation in multichannel optical transmission. Local or self-iteration is performed one or more times between an expected propagation decision feedback equalizer and a soft demapper. Following local iteration, a soft decision forward error correction decoder determines bit log-likelihood ratios, which are fed back to the expected propagation decision feedback equalizer and soft demapper for further self-iteration. Global iteration involving the decoder can also be performed one or more times before a bitstream is decoded.

First compensation circuitry includes a first digital filter compensating a phase difference between a phase of a symbol of a received signal and a sampling timing, and first filter coefficient calculation circuitry calculating a filter coefficient of the first digital filter as a first filter coefficient. Second filter coefficient calculation circuitry calculates, as a second filter coefficient, a filter coefficient for adaptive equalization that compensates distortion due to temporally changing polarization dispersion, based on an output of the first digital filter. Coefficient combination circuitry combines the first filter coefficient and the second filter coefficient. Second compensation circuitry includes a second digital filter which uses a filter coefficient combined by the coefficient combination circuitry and performs a compensation of the phase difference between the phase of the symbol of the received signal and the sampling timing, and a process of the adaptive equalization at the same time.

First compensation circuitry includes a first digital filter compensating a phase difference between a phase of a symbol of a received signal and a sampling timing, and first filter coefficient calculation circuitry calculating a filter coefficient of the first digital filter as a first filter coefficient. Second filter coefficient calculation circuitry calculates, as a second filter coefficient, a filter coefficient for adaptive equalization that compensates distortion due to temporally changing polarization dispersion, based on an output of the first digital filter. Coefficient combination circuitry combines the first filter coefficient and the second filter coefficient. Second compensation circuitry includes a second digital filter which uses a filter coefficient combined by the coefficient combination circuitry and performs a compensation of the phase difference between the phase of the symbol of the received signal and the sampling timing, and a process of the adaptive equalization at the same time.