Abstract: An apparatus includes an optical PSK transmitter configured to output carrier-suppressed optical signal phase-modulated according to a M-PSK constellation without substantial amplitude modulation. The apparatus includes an optical phase modulator, a driver configured to drive the modulator with a PAM-N electrical signal, N>M, and a signal encoder configured to map an input bit stream to the PAM-N electrical signal.

Abstract: A machine-implemented method of constructing multidimensional constellations having increased minimum distances between the constellation symbols thereof compared to those of comparable conventional constellations, e.g., QPSK and QAM constellations. An example multidimensional constellation so constructed may have eight or more dimensions and may be mapped onto degrees of freedom selected from, e.g., time, space, wavelength, polarization, and the in-phase and quadrature-phase components, of the optical field. The disclosed method is beneficially used to generate multidimensional modulation formats characterized by constant total optical transmit power per modulation time slot and/or applicable to the transmission of multidimensional constellation symbols having separate parts thereof primarily carried by different respective guided modes of the optical fiber. Example methods and apparatus for implementing such multidimensional modulation formats are also disclosed herein.

Abstract: A machine-implemented method of constructing multidimensional constellations having increased minimum distances between the constellation symbols thereof compared to those of comparable conventional constellations, e.g., QPSK and QAM constellations. An example multidimensional constellation so constructed may have eight or more dimensions and may be mapped onto degrees of freedom selected from, e.g., time, space, wavelength, polarization, and the in-phase and quadrature-phase components, of the optical field. The disclosed method is beneficially used to generate multidimensional modulation formats characterized by constant total optical transmit power per modulation time slot and/or applicable to the transmission of multidimensional constellation symbols having separate parts thereof primarily carried by different respective guided modes of the optical fiber. Example methods and apparatus for implementing such multidimensional modulation formats are also disclosed herein.

Abstract: An optical data receiver includes optical hybrids, light detectors and a digital signal processor. Each optical hybrid outputs mixtures of a corresponding one of the polarization components of a received data-modulated optical carrier with reference light. Each light detector outputs digital measurements of the mixtures from a corresponding one of the optical hybrids. The digital signal processor identifies data symbols of a constellation having parts transmitted on both polarization components of the data-modulated optical carrier responsive to receipt of the digital measurements. The transmitted data-modulated optical carrier has about a same total light intensity in each modulation time slot thereof. Each data symbol is defined by in-phase and quadrature-phase electric field coordinates of both polarization components. Pairs of in-phase and quadrature-phase electric coordinates of each of the polarization components are on a preselected set of one or more concentric circles about an origin.

Abstract: An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

Abstract: An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

Abstract: An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

Abstract: An optical data receiver includes optical hybrids, light detectors and a digital signal processor. Each optical hybrid outputs mixtures of a corresponding one of the polarization components of a received data-modulated optical carrier with reference light. Each light detector outputs digital measurements of the mixtures from a corresponding one of the optical hybrids. The digital signal processor identifies data symbols of a constellation having parts transmitted on both polarization components of the data-modulated optical carrier responsive to receipt of the digital measurements. The transmitted data-modulated optical carrier has about a same total light intensity in each modulation time slot thereof. Each data symbol is defined by in-phase and quadrature-phase electric field coordinates of both polarization components. Pairs of in-phase and quadrature-phase electric coordinates of each of the polarization components are on a preselected set of one or more concentric circles about an origin.

Abstract: We disclose an optical transport system configured to reduce nonlinear signal distortions using an electronic phase rotation, the phase value of which is determined using pre-filtering, e.g., via a low-pass filter, of the digital samples representing an optical communication signal prior to applying a squaring operation to the digital samples. In some embodiments, the phase value used in the electronic phase rotation can be determined using double filtering of the digital samples that, in addition to the pre-filtering, employs post-filtering, e.g., via another low-pass filter, of the digital samples generated by the squaring operation. The electronic phase rotation can be implemented as part of a backward-propagation algorithm that, in addition to reducing the nonlinear signal distortions, provides at least partial dispersion compensation. In various embodiments, the corresponding backward-propagation module can be incorporated into the transmitter's digital signal processor (DSP) or the receiver's DSP.

Abstract: An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

Abstract: An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

Abstract: An apparatus includes an optical transmitter having a plurality of optical data modulators and an end-face coupler. Each of the optical data modulators is configured to output a corresponding data-modulated optical carrier. The optical end-face coupler is configured to direct the data-modulated optical carriers into a pattern of light beams to illuminate an end-face of a multi-mode optical fiber with a pattern of light spots. The optical end-face coupler is configured to cause each of the data-modulated optical carriers to excite a set of orthonormal optical propagating modes of the multi-mode optical fiber. Some of the orthonormal optical propagating modes of the set have nontrivially differing intensity and/or phase profiles.

Abstract: An apparatus includes an all-optical transmission line having, at one wavelength, a pair of relatively orthogonal optical propagating modes whose local group velocities differ along a part of the all-optical transmission line. The all-optical transmission line is formed by a sequence of optically end-connected multi-mode fiber segments. The segments include, at least, 80% of the optical path length of the all-optical transmission line. Each segment is configured such that a differential group delay between the pair varies monotonically there along and changes by, at least, 200 pico-seconds thereon.

Abstract: An apparatus includes a multi-mode optical fiber having a selected plurality of optical propagating modes. The selected plurality may include only a proper subset of or may include all of the optical propagating modes of the multi-mode optical fiber. Each optical propagating mode of the selected plurality has a group velocity that varies over a corresponding range for light in, at least, one of the optical telecommunications C-band, the optical telecommunications L-band, and the optical telecommunications S-band. The ranges corresponding to different ones of the modes of the selected plurality are non-overlapping. The ranges of a group velocity-adjacent pair of the ranges are separated by a nonzero gap of less than about 10,000 meters per second.

Abstract: We disclose an optical transport system configured to reduce nonlinear signal distortions using an electronic phase rotation, the phase value of which is determined using pre-filtering, e.g., via a low-pass filter, of the digital samples representing an optical communication signal prior to applying a squaring operation to the digital samples. In some embodiments, the phase value used in the electronic phase rotation can be determined using double filtering of the digital samples that, in addition to the pre-filtering, employs post-filtering, e.g., via another low-pass filter, of the digital samples generated by the squaring operation. The electronic phase rotation can be implemented as part of a backward-propagation algorithm that, in addition to reducing the nonlinear signal distortions, provides at least partial dispersion compensation. In various embodiments, the corresponding backward-propagation module can be incorporated into the transmitter's digital signal processor (DSP) or the receiver's DSP.

Abstract: An apparatus, e.g. an optical data transmission device, is configured to propagate a non-return-to-zero (NRZ) modulated optical communication signal. A plurality of optical amplifiers are configured to receive the modulated optical signal. An optical transmission line includes a sequence of at least five spans of optical fiber, with each adjacent pair of the spans being connected by one of the optical amplifiers. Between about 10% and about 75% of the optical amplifiers include a dispersion compensation module (DCM) and a remainder of the optical amplifiers do not include a DCM, and at least two of said optical amplifiers are optically coupled between a first and a second optical add-drop multiplexer.

Abstract: We disclose a signal-routing method directed at improving the throughput of an optical network by taking into account the fiber nonlinearity in the process of solving a joint signal-routing and power-control problem for the optical network. Based on the obtained solution, a network controller may set the signal-routing configurations of the various network nodes and the optical gains of the various optical amplifiers to enable the optical network to carry the traffic in a manner that results in a higher throughput than that achievable with the use of conventional signal-routing and/or power-control methods.

Abstract: We disclose a signal-routing method directed at improving the throughput of an optical network by taking into account the fiber nonlinearity in the process of solving a joint signal-routing and power-control problem for the optical network. Based on the obtained solution, a network controller may set the signal-routing configurations of the various network nodes and the optical gains of the various optical amplifiers to enable the optical network to carry the traffic in a manner that results in a higher throughput than that achievable with the use of conventional signal-routing and/or power-control methods.

Abstract: A WDM system having at least two channels, each of which employs two polarizations, is arranged so that the start times of symbols carried by one polarization of a channel are displaced in time from the start times of symbols carried by the other polarization of that channel, e.g., the start time for each symbol on one polarization is not substantially synchronized with the closest-in-time symbol start time on the other polarization of that channel. Preferably, the data signals are modulated using a return-to-zero (RZ) format and the start times of the symbols of the data signal carried by one polarization of a channel is offset from the start time of the symbols data signal carried by the other polarization of that channel by between 20% to 80%—preferably 50%—of the symbol period of the data signals, when the data signals have the same symbol period.

Abstract: An optical receiver comprising an optical-to-electrical converter and a digital processor having one or more equalizer stages. The optical-to-electrical converter is configured to mix an optical input signal and an optical local-oscillator signal to generate a plurality of electrical digital measures of the optical input signal. The digital processor is configured to process the electrical digital measures to recover the data carried by the optical input signal. At least one of the equalizer stages is configured to perform signal-equalization processing in which the electrical digital measures and/or digital signals derived from the electrical digital measures are being treated as linear combinations of arbitrarily coupled signals, rather than one or more pairs of 90-degree phase-locked I and Q signals.