Abstract: A method for all-optical reduction of inter-channel crosstalk for spectrally overlapped optical signals for maximizing utilization of an available spectrum includes receiving a plurality of spectrally overlapped optical signals modulated with data. The method further includes generating conjugate copies of each of the plurality of optical signals using non-linear optics. The method further includes selecting the conjugate copies and adjusting an amplitude, a phase, and a delay of the conjugate copies. The method further includes performing inter-channel interference (ICI) compensation on the spectrally overlapped optical signals in an optical domain by adding the adjusted conjugate copies to the spectrally overlapped optical signals.

Abstract: A method for all-optical reduction of inter-channel crosstalk for spectrally overlapped optical signals for maximizing utilization of an available spectrum includes receiving a plurality of spectrally overlapped optical signals modulated with data. The method further includes generating conjugate copies of each of the plurality of optical signals using non-linear optics. The method further includes selecting the conjugate copies and adjusting an amplitude, a phase, and a delay of the conjugate copies. The method further includes performing inter-channel interference (ICI) compensation on the spectrally overlapped optical signals in an optical domain by adding the adjusted conjugate copies to the spectrally overlapped optical signals.

Abstract: A system includes a transmitter with multiple transmit devices each having an OAM multiplexer that converts multiple input signals into an OAM beam. Each transmit device outputs a coaxial group of orthogonal OAM beams. The system also includes a receiver that has multiple receive devices each having an OAM demultiplexer that receives the group of OAM beams from a corresponding transmit device. The OAM demultiplexer also converts the coaxial group of mutually orthogonal OAM beams into a plurality of received signals corresponding to input signals represented by the OAM beams. The receiver also includes a MIMO processor that has an equalizer that determines a transfer function corresponding to crosstalk of each of the plurality of received signals. The MIMO processor also reduces the crosstalk of each of the plurality of received signals based on the transfer function and updates the transfer function.

Abstract: A method for transmitting an optical signal through a first channel and a second channel includes coupling the optical signal with a first pair of comb lines separated by a spacing frequency to create an optical signal copy that is spaced from the optical signal by the spacing frequency. The method also includes filtering a first slice of the optical signal and a second slice of the optical signal copy. The method also includes transmitting the first slice of the optical signal and the second slice of the optical signal through the first channel and the second channel, respectively. The method also includes stitching the first slice of the optical signal with the second slice of the optical signal copy to generate a stitched version of the original optical signal.

Abstract: Methods, systems, and apparatus for phase-sensitive regeneration of a signal without a phase-locked loop and using Brillouin amplification. The system for phase-sensitive regeneration includes a data channel, one or more pumps and a mixing stage. The one or more pumps are coupled with the data channel. The mixing stage is coupled with the data channel and is for processing a data signal that is combined with an output of the one or more pumps and idler or higher harmonic. The mixing stage is configured to amplify the idler or higher harmonic using Brillouin amplification in a Brillouin gain medium to keep the one or more pumps and the data channel phase-locked.

Abstract: A method for transmitting an optical signal through a first channel and a second channel includes coupling the optical signal with a first pair of comb lines separated by a spacing frequency to create an optical signal copy that is spaced from the optical signal by the spacing frequency. The method also includes filtering a first slice of the optical signal and a second slice of the optical signal copy. The method also includes transmitting the first slice of the optical signal and the second slice of the optical signal through the first channel and the second channel, respectively. The method also includes stitching the first slice of the optical signal with the second slice of the optical signal copy to generate a stitched version of the original optical signal.

Abstract: A method, apparatus and system for estimating frequency offset that includes: a first calculating unit to calculate a correlation value of each of multiple sequences with different lengths according to a received signal containing the sequences with different lengths, where each of the sequences is repeatedly transmitted many times in the signal; a second calculating unit to calculate a decimal frequency according to the correlation value; a first determining unit to determine an integer frequency offset according to the decimal frequency offset to which each of the sequences corresponds; and a second determining unit to determine a total frequency offset according to the decimal frequency offset and the integer frequency offset.

Abstract: A system includes a transmitter with multiple transmit devices each having an OAM multiplexer that converts multiple input signals into an OAM beam. Each transmit device outputs a coaxial group of orthogonal OAM beams. The system also includes a receiver that has multiple receive devices each having an OAM demultiplexer that receives the group of OAM beams from a corresponding transmit device. The OAM demultiplexer also converts the coaxial group of mutually orthogonal OAM beams into a plurality of received signals corresponding to input signals represented by the OAM beams. The receiver also includes a MIMO processor that has an equalizer that determines a transfer function corresponding to crosstalk of each of the plurality of received signals. The MIMO processor also reduces the crosstalk of each of the plurality of received signals based on the transfer function and updates the transfer function.

Abstract: Methods, systems, and apparatus for phase-sensitive regeneration of a signal without a phase-locked loop and using Brillouin amplification. The system for phase-sensitive regeneration includes a data channel, one or more pumps and a mixing stage. The one or more pumps are coupled with the data channel. The mixing stage is coupled with the data channel and is for processing a data signal that is combined with an output of the one or more pumps and idler or higher harmonic. The mixing stage is configured to amplify the idler or higher harmonic using Brillouin amplification in a Brillouin gain medium to keep the one or more pumps and the data channel phase-locked.

Abstract: A system for estimating cross-phase modulation (XPM) impairments, wherein the method comprises: determining, according to a pump Jones matrix of a pump channel and a probe Jones matrix of a probe channel of each of fiber spans except for the first fiber span in a fiber transmission system, a polarization mode dispersion (PMD)-induced relative polarization status rotation matrix between channels of the each of fiber spans; and determining, according to the rotation matrix of the each of fiber spans, dispersion of a pump signal of the each of fiber spans, differential delay of the pump signal relative to a probe signal of the each of fiber spans and a gain of the each of fiber spans, polarization crosstalk and phase noise of the XPM impairments in the fiber transmission system. This allows the XPM impairments in the effect of the polarization mode dispersion to be quickly and accurately estimated.

Abstract: A method, apparatus and system for estimating frequency offset that includes: a first calculating unit to calculate a correlation value of each of multiple sequences with different lengths according to a received signal containing the sequences with different lengths, where each of the sequences is repeatedly transmitted many times in the signal; a second calculating unit to calculate a decimal frequency according to the correlation value; a first determining unit to determine an integer frequency offset according to the decimal frequency offset to which each of the sequences corresponds; and a second determining unit to determine a total frequency offset according to the decimal frequency offset and the integer frequency offset.

Abstract: A system for estimating cross-phase modulation (XPM) impairments, wherein the method comprises: determining, according to a pump Jones matrix of a pump channel and a probe Jones matrix of a probe channel of each of fiber spans except for the first fiber span in a fiber transmission system, a polarization mode dispersion (PMD)-induced relative polarization status rotation matrix between channels of the each of fiber spans; and determining, according to the rotation matrix of the each of fiber spans, dispersion of a pump signal of the each of fiber spans, differential delay of the pump signal relative to a probe signal of the each of fiber spans and a gain of the each of fiber spans, polarization crosstalk and phase noise of the XPM impairments in the fiber transmission system.