Abstract: An optical transport system is configured to use a modulation scheme in which a phase rotation applied to a sequence of PSK or QAM constellation symbols encoding a codeword of an FEC code produces a modified sequence of PSK or QAM constellation symbols encoding a bit-word that is not a valid codeword of that FEC code. Based on this property of the modulation scheme, an optical receiver may be configured to relatively accurately recover the absolute phase of the optical carrier wave of the received modulated optical signal by applying maximum likelihood sequence estimation processing to each portion of the signal carrying a valid codeword of the FEC code. For example, for a modulation scheme employing a 2n-PSK constellation, the optical receiver may be able to recover the absolute phase of the optical carrier wave with an accuracy that is better than 360/2n degrees.

Abstract: An optical transport system is configured to use a modulation scheme in which a phase rotation applied to a sequence of PSK or QAM constellation symbols encoding a codeword of an FEC code produces a modified sequence of PSK or QAM constellation symbols encoding a bit-word that is not a valid codeword of that FEC code. Based on this property of the modulation scheme, an optical receiver may be configured to relatively accurately recover the absolute phase of the optical carrier wave of the received modulated optical signal by applying maximum likelihood sequence estimation processing to each portion of the signal carrying a valid codeword of the FEC code. For example, for a modulation scheme employing a 2n-PSK constellation, the optical receiver may be able to recover the absolute phase of the optical carrier wave with an accuracy that is better than 360/2n degrees.

Abstract: An optical transport system that transmits data using relatively short FEC-encoded data frames. The corresponding modulated optical signals are decoded at an optical receiver using frame-based maximum likelihood sequence estimation that relies on data redundancy present in each FEC-encoded data frame for the determination of its source bits. In some embodiments, the modulated optical signals carrying the FEC-encoded data frames are generated using a polarization-division-multiplexed constellation. The FEC-coding rate and frame length can be adjusted without changing the constellation, which advantageously enables the optical transport system to dynamically adapt its transmission format to the changing link conditions in a manner that results in better overall receiver sensitivity than that achieved with comparable bit-rate-adaptation methods that rely on a constellation change rather than on a change of the FEC-coding rate.

Abstract: A system, e.g. for optical communication, includes an I-Q modulator and a transmission signal processor. The I-Q modulator is configured to modulate a first light source in response to first I and Q modulation signals. The transmission signal processor is configured to receive a data stream including data corresponding to a first data subchannel. The processor maps the data subchannel to an optical transmission subchannel and outputs the first I and Q modulation signals. The I and Q modulation signals modulate the light source to produce an optical transmission signal that includes wavelength components corresponding to the optical transmission subchannel.

Abstract: Various embodiments of a 16-QAM (quadrature-amplitude-modulation) constellation having one or more subsets of its sixteen constellation points arranged within respective one or more relatively narrow circular bands. Each of the subsets includes constellation points of at least two different amplitudes and may have between about six and about ten constellation points. Each of the circular bands may have a width that is between about 3% and about 20% of the maximum amplitude in the constellation.

Abstract: A system, e.g. for optical communication, includes an I-Q modulator and a transmission signal processor. The I-Q modulator is configured to modulate a first light source in response to first I and Q modulation signals. The transmission signal processor is configured to receive a data stream including data corresponding to a first data subchannel. The processor maps the data subchannel to an optical transmission subchannel and outputs the first I and Q modulation signals. The I and Q modulation signals modulate the light source to produce an optical transmission signal that includes wavelength components corresponding to the optical transmission subchannel.

Abstract: An optical transport system that transmits data using relatively short FEC-encoded data frames. The corresponding modulated optical signals are decoded at an optical receiver using frame-based maximum likelihood sequence estimation that relies on data redundancy present in each FEC-encoded data frame for the determination of its source bits. In some embodiments, the modulated optical signals carrying the FEC-encoded data frames are generated using a polarization-division-multiplexed constellation. The FEC-coding rate and frame length can be adjusted without changing the constellation, which advantageously enables the optical transport system to dynamically adapt its transmission format to the changing link conditions in a manner that results in better overall receiver sensitivity than that achieved with comparable bit-rate-adaptation methods that rely on a constellation change rather than on a change of the FEC-coding rate.

Abstract: Various embodiments of a 16-QAM (quadrature-amplitude-modulation) constellation having one or more subsets of its sixteen constellation points arranged within respective one or more relatively narrow circular bands. Each of the subsets includes constellation points of at least two different amplitudes and may have between about six and about ten constellation points. Each of the circular bands may have a width that is between about 3% and about 20% of the maximum amplitude in the constellation.

Abstract: In one embodiment, a coherent optical receiver has an optical detector coupled to a digital processor. The optical detector mixes a received modulated optical signal with a local-oscillator signal to produce a digital measure of the modulated optical signal. The digital processor processes the digital measure using a primary carrier- and data-recovery (CDR) stage and one or more secondary CDR stages serially connected to one another. The processing performed in each secondary CDR stage is decision-directed and uses the symbol estimate generated by the preceding CDR stage to obtain a respective estimate of the carrier-phase offset and a respective symbol estimate. Since each subsequent CDR stage typically improves the accuracies of its estimates compared to those of the preceding CDR stage(s), the receiver has a lower bit-error rate than a receiver employing a single CDR stage.

Abstract: In one embodiment, a coherent optical receiver has an optical detector coupled to a digital processor. The optical detector mixes a received modulated optical signal with a local-oscillator signal to produce a digital measure of the modulated optical signal. The digital processor processes the digital measure using a primary carrier- and data-recovery (CDR) stage and one or more secondary CDR stages serially connected to one another. The processing performed in each secondary CDR stage is decision-directed and uses the symbol estimate generated by the preceding CDR stage to obtain a respective estimate of the carrier-phase offset and a respective symbol estimate. Since each subsequent CDR stage typically improves the accuracies of its estimates compared to those of the preceding CDR stage(s), the receiver has a lower bit-error rate than a receiver employing a single CDR stage.