In order to estimate a polarization fluctuation speed with high accuracy independently of the quality of a received signal, a polarization-fluctuation estimating device according to the present invention includes: a polarization de-multiplexing unit that generates a single-polarization optical signal from an input polarization-multiplexed optical signal; a photoelectric converting unit that converts the generated optical signal into an electrical signal; and an estimation unit that estimates the polarization fluctuation speed of the polarization-multiplexed optical signal in accordance with the electrical signal.

A method for preventing nonlinear interference in an optical communication system. The method may include selecting an optical signal of a first optical channel. The method may include determining an estimate of inter-channel nonlinear interference to the optical signal of the first optical channel. The inter-channel nonlinear interference may be generated by one or more optical signals transmitted over a second optical channel in the optical communication system. The method may include determining one or more linear filters based on the estimate of the inter-channel nonlinear interference. The method may include pre-distorting an optical signal for transmission over the second optical channel using the one or more linear filters. The pre-distorted optical signal may be configured for reducing the inter-channel nonlinear interference to the first optical signal of the first optical channel. The method may include transmitting the pre-distorted optical signal over the second optical channel through an optical transmission medium.

Methods and systems for decoding symbols transmitted over an optical channel having a cross-polarization modulation (XPolM) impairment, wherein an optical signal is polarized to encode the symbols on an x-polarization and an y-polarization before transmitted. The method including receiving the optical signal transmitted over the optical channel. Sampling the optical signal to produce a sequence of digital samples, wherein each digital sample includes a measurement of each polarization of the optical signal at an instance of time. Selecting a subset of the sequence of digital samples that includes a digital sample and neighboring digital samples on the sequence. Repeating the selecting and the determining for each digital sample remaining in the sequence of digital samples to produce a sequence of cross-talk coefficients; and decoding some of the symbols from the sequence of digital samples using cross-talk models with corresponding cross-talk coefficients, wherein method steps are performed using a processor.

Methods and systems for decoding symbols transmitted over an optical channel having a cross-polarization modulation (XPolM) impairment, wherein an optical signal is polarized to encode the symbols on an x-polarization and an y-polarization before transmitted. The method including receiving the optical signal transmitted over the optical channel. Sampling the optical signal to produce a sequence of digital samples, wherein each digital sample includes a measurement of each polarization of the optical signal at an instance of time. Selecting a subset of the sequence of digital samples that includes a digital sample and neighboring digital samples on the sequence. Repeating the selecting and the determining for each digital sample remaining in the sequence of digital samples to produce a sequence of cross-talk coefficients; and decoding some of the symbols from the sequence of digital samples using cross-talk models with corresponding cross-talk coefficients, wherein method steps are performed using a processor.

A control device which controls an operation of a compensation device which compensates for birefringence and/or polarization mode dispersion, which is received by signal light having propagated through an optical transmission line, by digital signal processing using a finite impulse response filter includes: a detection signal reception unit which receives a detection signal which is a signal indicating a detection result of a detection device which optically detects polarization fluctuation in the optical transmission line; and a setting unit which decides a setting regarding an update frequency or an update interval of the number of taps of the finite impulse response filter or an update frequency or an update interval of a tap coefficient of the finite impulse response filter, based on the detection result of the detection device.

An optical data communication system includes an optical transmitter and an optical receiver. A polarization-maintaining optical data communication link extends from an optical output of the optical transmitter to an optical input of the optical receiver. The polarization-maintaining optical data communication link includes at least two sections of polarization-maintaining optical fiber optically connected through an optical connector. The at least two sections of polarization-maintaining optical fiber have different lengths. The optical connector is configured to optically align a fast polarization axis of a first polarization-maintaining optical fiber to a slow polarization axis of a second polarization-maintaining optical fiber. The optical connector is also configured to optically align a slow polarization axis of the first polarization-maintaining optical fiber to a fast polarization axis of the second polarization-maintaining optical fiber.

There is provided an optical source. The optical source comprises a reflective optical amplifier configured to generate an optical signal, the optical signal comprising an amplified spontaneous light emission having a plurality of light modes each having a respective wavelength. The optical source further comprises a reflective mirror, spaced from the reflective optical amplifier, and arranged to receive the optical signal and to rotate a polarization of each light mode in the received optical signal, to form a further optical signal. The optical source further comprises an optical power splitter arranged to receive the further optical signal and to split the further optical signal into a first optical signal which is directed to the reflective optical amplifier for amplification thereby, and a second optical signal. The optical source further comprises an output arranged to output the second optical signal. There is also provided a communications network optical apparatus and a communications network base station.

Methods, systems, and apparatus, for an external cavity FP laser. In one aspect, an apparatus is provided that includes a FP laser diode; a Faraday rotator (FR) coupled to receive an optical output of the FP laser diode and that rotates a polarization of the optical output; an optical fiber coupled at a first end to receive the output of the FR; a WDM filter coupled to a second end of the optical fiber to receive the optical signal from the optical fiber; and a FRM coupled directly or indirectly to an output of the WDM filter, wherein an optical output of the WDM filter is partially reflected by the FRM such that the polarization of a reflected beam is rotated, and wherein the reflected optical signal then passes through the FR with its polarization being rotated by the FR before it is injected back into the FP laser diode.

A signal equalizer for compensating impairments of an optical signal received through a link of a high speed optical communications network. At least one set of compensation vectors are computed for compensating at least two distinct types of impairments. A frequency domain processor is coupled to receive respective raw multi-bit in-phase (I) and quadrature (Q) sample streams of each received polarization of the optical signal. The frequency domain processor operates to digitally process the multi-bit sample streams, using the compensation vectors, to generate multi-bit estimates of symbols modulated onto each transmitted polarization of the optical signal. The frequency domain processor exhibits respective different responses to each one of the at least two distinct types of impairments.

A digital signal processor (DSP) of an optical receiver may receive information representing a polarization multiplexed signal including tone information. The polarization multiplexed signal may have an uncorrected state of polarization (SOP). The DSP may determine sets of Stokes parameters based on the tone information. The DSP may determine a set of polarization parameters based on the sets of Stokes parameters. The DSP may apply, based on the set of polarization parameters, a set of operations to the information representing the polarization multiplexed signal. An operation, of the set of operations, may represent a rotation or a phase retardation of the polarization multiplexed signal and may correspond to a polarization parameter of the set of polarization parameters. The set of operations may be applied to the information representing the polarization multiplexed signal in order to generate information representing the polarization multiplexed signal with a corrected SOP.