An optical transmission apparatus for transmitting wavelength-multiplexed light, the optical transmission apparatus includes: an optical transmitter configured to transmit light of a third wavelength to be arranged between a first wavelength and a second wavelength adjacent to the third wavelength in the wavelength-multiplexed light, and a controller configured to control a bandwidth of the light of the third wavelength to be arranged in a first bandwidth narrower than a spacing between the first wavelength and the second wavelength.

A system comprises: a polarization state aligner (PSA) comprising: an input port; a first polarization beam splitter (PBS) coupled to the input port; a first phase shifter (PS) coupled to the first PBS; a first polarization rotator (PR) coupled to the first PBS; a first beam splitter (BS) coupled to the first PS and the first PR; a first output port coupled to the first BS; and a second output port coupled to the first BS.

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.

A method of suppressing polarization-dependent loss in a signal. A constant-intensity, analog, optical signal with modulating polarization is transmitted through an optical communications link. The constant-intensity, analog, optical signal with modulating polarization includes an analog radio frequency signal impressed upon a polarization-modulated, laser signal. A polarization-dependent loss of the communications link is determined, the polarization-dependent loss inducing an induced phase shift in the constant-intensity, analog, optical signal with modulating polarization. The constant-intensity, analog, optical signal with modulating polarization is re-oriented using a polarization transformer so as to suppress the induced phase shift.

A state of polarization tracking recovery method and apparatus. The apparatus at least includes a processor configured to fit Stokes vectors to which predetermined symbols correspond of two states of polarization in a received dual-polarization multiplexing optical signal on a Poincare sphere to obtain a fitted plane. The processor calculates a compensation matrix for polarization-dependent loss (PDL) in a Jones space by moving a center of the fitted plane to the origin of the Poincare sphere, and calculates a demultiplexing matrix used for polarization demultiplexing in a Jones space by rotating the fitted plane with the center being moved to the origin until a normal vector of the fitted plane is parallel with a first axis of the Stokes space and rotating the fitted plane with the center being moved to the origin to a plane constituted by a second axis and a third axis of the Stokes space.

Systems and methods are provided for receiving an optical signal from an optical fiber, including: coupling via an optical coupler the optical signal from an optical fiber into first and second waveguides, wherein the optical signal comprises TE and TM polarized optical signals and the optical coupler couples the TE polarized optical signal into the first waveguide and the TM polarized optical signal into the second waveguide; equalizing the TE and TM polarized optical signals from the coupler to equalize optical power levels of the TE and TM polarized optical signals; optically combining the equalized TE and TM polarized optical signals; and transmitting the combined optical signal to a photodetector.

Provided is an optical communication system comprising a polarization-diversity optical power supply capable of supplying light over a non-polarization-maintaining optical fiber to a polarization-sensitive modulation device. In an example embodiment, the polarization-diversity optical power supply operates to accommodate random polarization fluctuations within the non-polarization-maintaining optical fiber and enables an equal-power split at a passive polarization splitter preceding the polarization-sensitive modulation device.

An optical network device includes a receiver that receives a polarization multiplexed optical signal and a processor. The processor separates an electric field information signal indicating the polarization multiplexed optical signal into first and second polarization components orthogonal to each other, generates third and fourth polarization components by controlling the first and second polarization components, calculates an evaluation value corresponding to a power of the third or fourth polarization component for each of a plurality of positions on a transmission line, calculates a variation in the evaluation value for a control amount for each of the plurality of positions, and decides whether a first position is a position to be detected based on a result of comparing a variation in an evaluation value for the first position with a variation in an evaluation value for a second position adjacent to the first position.

A polarization dependent loss (PDL) compensation device for an optical system can be configured to output a compensating PDL to at least partially cancel a PDL of the optical system. In certain embodiments, the device can include a first polarization controller configured to modify a state of polarization of an optical signal, a PDL emulator disposed upstream of the first polarization controller and configured to output the compensating PDL upstream of the first polarization controller, and a second polarization controller disposed upstream of the PDL emulator and configured to modify a state of polarization of the optical signal upstream of the PDL emulator.

An optical network device includes a receiver that receives a polarization multiplexed optical signal and a processor. The processor separates an electric field information signal indicating the polarization multiplexed optical signal into first and second polarization components orthogonal to each other, generates third and fourth polarization components by controlling the first and second polarization components, calculates an evaluation value corresponding to a power of the third or fourth polarization component for each of a plurality of positions on a transmission line, calculates a variation in the evaluation value for a control amount for each of the plurality of positions, and decides whether a first position is a position to be detected based on a result of comparing a variation in an evaluation value for the first position with a variation in an evaluation value for a second position adjacent to the first position.