Methods, systems, and apparatus, including computer programs encoded on computer storage media, for applying non-linearity to digital subcarriers. A receiver includes a detector circuit operable to receive a first optical signal over an optical link, the first optical signal carrying first data. The receiver includes a carrier recovery estimation circuit operable to generate compensated data by correcting errors in the first data. The receiver includes a non-linear coefficient estimation circuit operable to (i) receive the compensated data, and (ii) estimate one or more non-linear coefficients, wherein information indicative of the estimated non-linear coefficients is transmitted over an optical network, such that a second optical signal is transmitted based, at least in part, on the estimated non-linear coefficients, the second optical signal being received by the receiver.

A bi-directional optical communication system employing a minimum number of single-mode high repetition rate pulsed optical signal sources to achieve cost efficiency while maintaining high data rates. The bi-directional optical communication system includes a first optical data processing unit and a second optical data processing unit. The first optical data processing unit modulates a pulsed optical source using a differential quadrature phase shift keying (DQPSK) modulation and two-level pulse amplitude (PAM-2) modulation and then demodulates it to achieve a pulse amplitude modulated signal. The second optical data processing unit reuses the same optical carrier by passing it through a regenerative wavelength converter to generate three pulsed optical carriers at different wavelengths and employs an On-off keying (OOK) modulation scheme. These carriers are employed to send uplink data at a same rate of as the downlink. As a result, large data is transmitted from one data center to another data center through a downlink and uplink free space optical link network.

A bi-directional optical communication system employing a minimum number of single-mode high repetition rate pulsed optical signal sources to achieve cost efficiency while maintaining high data rates. The bi-directional optical communication system includes a first optical data processing unit and a second optical data processing unit. The first optical data processing unit modulates a pulsed optical source using a differential quadrature phase shift keying (DQPSK) modulation and two-level pulse amplitude (PAM-2) modulation and then demodulates it to achieve a pulse amplitude modulated signal. The second optical data processing unit reuses the same optical carrier by passing it through a regenerative wavelength converter to generate three pulsed optical carriers at different wavelengths and employs an On-off keying (OOK) modulation scheme. These carriers are employed to send uplink data at a same rate of as the downlink. As a result, large data is transmitted from one data center to another data center through a downlink and uplink free space optical link network.

An apparatus and method to measure nonlinear system noises may include a processor to generate a bilateral notch signal, a unilateral notch signal and a multi-tone signal; to measure power of an additive Gaussian white noise of a nonlinear system by using the multi-tone signal; to measure a first power-to-noise ratio of the nonlinear system by using the bilateral notch signal; to measure a second power-to-noise ratio of the nonlinear system by using the unilateral notch signal. The processor is to calculate a nonlinear power-to-noise ratio of the nonlinear system and a power-to-noise ratio introduced by IQ imbalance according to the power of the additive Gaussian white noise, the first power-to-noise ratio and the second power-to-noise ratio.

This method includes optimizing, by a gradient descent method, a first parameter used in back propagation processing and associated with XPM and a second parameter used in the back propagation processing and associated with SPM and XPM, wherein the back propagation processing is processing to estimate a waveform at a time of transmission by alternately calculating linear terms and nonlinear terms in a nonlinear Schrdinger equation after receiving an optical signal whose waveform shape changed in a transmission line and digitizing a waveform of the received optical signal, and correct, for each channel of plural channels in the transmission line at a time of wavelength-division multiplexing transmission, waveform distortion caused by SPM that occurs in the channel and waveform distortion caused by XPM that occurs in relation with channels other than the channel; and executing the back propagation processing by using the optimized first and second parameters.

Aspects of the subject disclosure may include, for example, obtaining a signal received at a coherent optical receiver, and equalizing the signal using a filter system, wherein the filter system includes a first filter that provides a first filtering characteristic, a second filter that provides a second filtering characteristic, and a third filter that provides a third filtering characteristic, wherein an adjustment rate of the first filter and an adjustment rate of the second filter are each at least ten times an adjustment rate of the third filter, and wherein the adjustment rate of the first filter is at least ten times the adjustment rate of the second filter. Other embodiments are disclosed.

A method for monitoring generalized optical signal-to-noise ratio (gOSNR) is provided, which is applied to monitoring of an optical signal received by a coherent receiver through a fiber link. The method includes: obtaining a first received waveform; obtaining a signal part of the first received waveform; obtaining a noise part of the first received waveform according to the signal part and the first received waveform; obtaining a first correlation between the noise part and a first template at a predetermined location on the fiber link, the first correlation indicating a signal power at the predetermined location; obtaining a second correlation between the noise part and a second template at the predetermined location on the fiber link, the second correlation indicating a signal power and noise power at the predetermined location; and obtaining gOSNR at the predetermined location according to the first correlation and the second correlation.

Aspects of the subject disclosure may include, for example, conducting blind learning of correction parameters for non-linear (NL) distortion associated with one or more components of a system, resulting in learned correction parameters, wherein the conducting is performed without a need to identify or estimate a reference input associated with the one or more components, and causing the learned correction parameters to be applied to an output signal associated with the one or more components to compensate for the NL distortion. Other embodiments are disclosed.

An all-optical signal processor includes one or more input ports configured to receive one or more optical signal channels, a first nonlinear optical processor configured to receive an input signal from the input port and having one or more sections of a first nonlinear medium, an optical phase conjugator optically configured to receive the output signal of the first nonlinear optical processor, a second nonlinear optical processor configured to receive an output signal from the optical phase conjugator and having one or more sections of a second nonlinear medium, and one or more output ports configured to receive the output signal from the second nonlinear optical processor. Variations of the all-optical signal processor can include a single nonlinear optical processor through which an output of the optical phase conjugator co-propagates or counter-propagates with the input signal.

A coherent optical transmission system includes two optical transceivers, each including a laser emitter, an optical splitting module, an optical modulator, an optical mixer and an optical detector. The laser emitter is configured to emit an initial light. The optical splitting module is configured to divide the light emitted by the laser emitter into a reference light and a signal light. The optical modulator is configured to modulate the signal light. The optical mixer is optically coupled to the optical splitting module. The optical mixer of the first optical transceiver is configured to optically mixing the reference light of the first optical transceiver and the signal light of the second optical transceiver, and the optical mixer of the second optical transceiver is configured to optically mixing the reference light of the second optical transceiver and the signal light of the first optical transceiver.