There is provided a method and apparatus for evaluating nonlinear impairment of an optical fiber link. The method includes partitioning a natural span of the optical fiber link into multiple sub-spans, each of the multiple sub-spans determined based on chromatic dispersion (CD) equivalence; The method further includes for each of the multiple sub-spans, acquiring sub-span function parameters and a sub-span input power indicative of input power at a particular sub-span, the sub-span function parameters including noise variance and correlations between the particular sub-span and others of the multiple sub-spans. The method additionally includes determining the nonlinear impairment of the optical fiber link based on the sub-span input power and the sub-span function parameters acquired for each of the multiple sub-spans.

The present application is directed to techniques and systems for extension of unrepeatered submarine fiber links to provide an increase in reach of unrepeatered fiber transmission. Both single channel unrepeatered systems and multiple channel unrepeatered systems can be used. The multiple channel unrepeatered systems can further employ nonlinearity compensation. The present application is also directed to methods of signal transmission using the unrepeatered systems.

The present application is directed to techniques and systems for extension of unrepeatered submarine fiber links to provide an increase in reach of unrepeatered fiber transmission. Both single channel unrepeatered systems and multiple channel unrepeatered systems can be used. The multiple channel unrepeatered systems can further employ nonlinearity compensation. The present application is also directed to methods of signal transmission using the unrepeatered systems.

A nonlinearity compensation circuit includes a detector that detects a combination of input levels of a plurality of input signals, a memory that saves a correction value information item to compensate for nonlinear distortion, the correction value information item being saved corresponding to the combination of the input levels, and a compensator that corrects a target signal among said plurality of input signals using the correction value information item acquired from the memory based on the combination of the input levels detected by the detector.

A nonlinearity compensation circuit includes a detector that detects a combination of input levels of a plurality of input signals, a memory that saves a correction value information item to compensate for nonlinear distortion, the correction value information item being saved corresponding to the combination of the input levels, and a compensator that corrects a target signal among said plurality of input signals using the correction value information item acquired from the memory based on the combination of the input levels detected by the detector.

A signal generation apparatus and method. The apparatus includes: a memory, and a processor coupled to the memory to control execution of a process to: perform dispersion processing on a two-dimensional reference signal to obtain a two-dimensional dispersion signal; perform at least one time of equiprobability processing, perturbation processing and isospectral processing on a two-dimensional input signal according to the two-dimensional dispersion signal; and output a two-dimensional isospectral equiprobability signal generated, when an equiprobability processed signal or an isospectral processed signal satisfies a predetermined condition, wherein in the equiprobability processing. In the equiprobability processing, the two-dimensional dispersion signal and the two-dimensional input signal are classified, so that numbers of constellation points of the two-dimensional input signal and the two-dimensional dispersion signal of same classes are identical, and the classified two-dimensional input signal and two-dimensional dispersion signal are sorted, so that the equiprobability processed signal maintain joint probability distribution.

A signal generation apparatus and method. The apparatus includes: a memory, and a processor coupled to the memory to control execution of a process to: perform dispersion processing on a two-dimensional reference signal to obtain a two-dimensional dispersion signal; perform at least one time of equiprobability processing, perturbation processing and isospectral processing on a two-dimensional input signal according to the two-dimensional dispersion signal; and output a two-dimensional isospectral equiprobability signal generated, when an equiprobability processed signal or an isospectral processed signal satisfies a predetermined condition, wherein in the equiprobability processing. In the equiprobability processing, the two-dimensional dispersion signal and the two-dimensional input signal are classified, so that numbers of constellation points of the two-dimensional input signal and the two-dimensional dispersion signal of same classes are identical, and the classified two-dimensional input signal and two-dimensional dispersion signal are sorted, so that the equiprobability processed signal maintain joint probability distribution.

A communication interface comprising a host with non-linear equalizers configured to perform non-linear equalization. Also part of the interface is a host to optic module channel electrically connecting the host to an optic module and the optic module. The optic module comprises a transmitter and a receiver. The transmitter includes a linear equalizer and an electrical to optical module configured to convert the equalized signal from the driver to an optical signal, and transmit the optical signal over a fiber optic cable, such that the transmitter does not perform non-linear processing. The receiver includes a photodetector, configured to convert the received optic signal to a received electrical signal, and a linear amplifier configured to perform linear amplification on the received electrical signal. A driver sends the amplified received signal over an optic module to host channel, such that the receive does not perform non-linear processing.

A communication interface comprising a host with non-linear equalizers configured to perform non-linear equalization. Also part of the interface is a host to optic module channel electrically connecting the host to an optic module and the optic module. The optic module comprises a transmitter and a receiver. The transmitter includes a linear equalizer and an electrical to optical module configured to convert the equalized signal from the driver to an optical signal, and transmit the optical signal over a fiber optic cable, such that the transmitter does not perform non-linear processing. The receiver includes a photodetector, configured to convert the received optic signal to a received electrical signal, and a linear amplifier configured to perform linear amplification on the received electrical signal. A driver sends the amplified received signal over an optic module to host channel, such that the receive does not perform non-linear processing.

Aspects of the present disclosure describe systems, methods and structures providing bidirectional optical fiber communication and sensing using the same fiber transmission band and bidirectional WDM fiber sharing such that communications channels and optical fiber sensing channel(s) coexist on the same fiber. As a result, nonlinear interaction between communications channels and interrogating pulse(s) of sensing are much reduced or eliminated.