A receiving unit (2020) generates a received frame from a modulated optical signal. The modulated optical signal is generated such that a transmission symbol is generated by mapping an encoded bit string obtained by encoding a transmission bit string to an m-dimensional symbol space, a transmission frame is generated by mapping the transmission symbol to an n-dimensional frame space (n<m), and an optical carrier wave is modulated by using the transmission frame. A converting unit (2040) generates candidate vectors (m-dimensional vectors belonging to a partial symbol space within the symbol space) by using a received frame. A first computing unit (2070) computes a probability of that the transmission symbol belonging to the partial symbol space is transmitted for each partial symbol space. A second computing unit (2080) computes a log-likelihood ratio of each bit of the encoded bit string by using the probability.

When a frequency deviation compensation amount is compensated for by use of frequency shift, a phase offset occurs between adjacent input blocks included in a plurality of input blocks as divided, with the result that an error occurs in a reconstructed bit sequence. A frequency deviation compensation system of the invention is characterized by comprising: a frequency deviation compensation means for compensating for a frequency deviation occurring in a signal by use of frequency shift; and a phase offset compensation means for compensating for a phase offset occurring, in the signal, due to the frequency shift.

Real-time systems and methods prevent duplication of independent signal streams in a coherent receiver subject to source separation controlled by multiplicative coefficients under adaptive feedback control. In various embodiments, this is achieved by first obtaining a first set of coefficients associated with a first signal stream and a second set of coefficients associated with a second signal stream. In response to the sets of coefficients satisfying a condition, the first set modified into a set of coefficients that is mutually orthogonal with respect to and replaces the second set of coefficients. The resulting series of coefficient values may then be used to perform source separation of independent signal streams without duplicating independent signal streams.

A system for estimating an imbalance between electrical-optical responses of an in-phase (I) channel and a quadrature (Q) channel in an optical amplitude and phase modulator (optical IQ modulator) includes an optical detector (PD), an analog-digital converter (ADC), and an imbalance operation unit that estimates an imbalance between electrical-optical responses of an I channel and a Q channel in the optical IQ modulator, wherein the imbalance operation unit includes an input signal information receiving unit that receives information regarding a first modulation signal, and an intensity information receiving unit that receives intensity information of the digitalized output signal from the ADC, and the imbalance operation unit estimates an imbalance between electrical-optical responses of an I channel and a Q channel in the optical IQ modulator using information regarding a first modulation signal and intensity information of the digitalized output signal.

An optical signal receiver includes a multimode waveguide for receiving a complex modulated optical signal, an optical resonator that receives the complex modulated optical signal from the multimode waveguide and converts the complex modulated optical signal to an intensity modulated signal, and a detector that is configured to convert the intensity modulated signal into an electrical signal, the electrical signal having an amplitude indicative of an intensity of the intensity modulated signal from the optical resonator, and that provides a detected signal.

When a frequency deviation compensation amount is compensated for by use of frequency shift, a phase offset occurs between adjacent input blocks included in a plurality of input blocks as divided, with the result that an error occurs in a reconstructed bit sequence. A frequency deviation compensation system of the invention is characterized by comprising: a frequency deviation compensation means for compensating for a frequency deviation occurring in a signal by use of frequency shift; and a phase offset compensation means for compensating for a phase offset occurring, in the signal, due to the frequency shift.

Coherent phase recovery method includes producing, with a transmit-side frequency-comb source, a first frequency-comb signal that includes a pilot tone and a first optical tone having a first center wavelength that differs from a pilot center wavelength of the pilot tone. The method also includes coherently modulating the first optical tone to yield a first modulated signal; and generating a second frequency-comb signal with a receive-side frequency-comb source driven by the pilot tone. The method also includes extracting, from the second frequency-comb signal, a first local-oscillator tone having the first center wavelength; and demodulating the first modulated signal by homodyning the first modulated signal with the first local-oscillator tone.

A coherent optical receiver includes equalizer circuitry having a plurality of taps, the equalizer circuitry being configured to receive an input signal and compensate for polarization mode dispersion affecting the input signal to generate a compensated input signal. The coherent optical receiver further includes error evaluation circuitry configured to calculate a determinant of a frequency-domain (FD) coefficient-based matrix using a plurality of tap signals from among the plurality of taps, adjust an error of convergence of the compensated input signal to generate an adjusted input signal, and iteratively adjust the determinant of the FD coefficient-based matrix based on the adjusted input signal to minimize the error of convergence.

When a frequency deviation compensation amount is compensated for by use of frequency shift, a phase offset occurs between adjacent input blocks included in a plurality of input blocks as divided, with the result that an error occurs in a reconstructed bit sequence. A frequency deviation compensation system of the invention is characterized by comprising: a frequency deviation compensation means for compensating for a frequency deviation occurring in a signal by use of frequency shift; and a phase offset compensation means for compensating for a phase offset occurring, in the signal, due to the frequency shift.

Real-time systems and methods prevent duplication of independent signal streams in a coherent receiver subject to source separation controlled by multiplicative coefficients under adaptive feedback control. In various embodiments, this is achieved by first obtaining a first set of coefficients associated with a first signal stream and a second set of coefficients associated with a second signal stream. In response to the sets of coefficients satisfying a condition, the first set modified into a set of coefficients that is mutually orthogonal with respect to and replaces the second set of coefficients. The resulting series of coefficient values may then be used to perform source separation of independent signal streams without duplicating independent signal streams.