Abstract: In a Forward Error Correction (FEC) technique, parity vectors are computed such that: each parity vector spans a set of frames; a subset of bits of each frame is associated with parity bits in each parity vector; and a location of parity bits associated with one frame in one parity vector is different from that of parity bits associated with the frame in another parity vector. Values of decoded bits of a first frame are deduced from known parity bits of a first parity vector having an effective length of one frame. For parity vectors having, an effective length greater than one frame, a Log Likelihood Ratio of each unknown parity bit associated with the first frame is updated based on known and unknown parity bits of each parity vector. The first frame is decoded using the deduced bit values and the updated LLR values.

Abstract: Described are an optical communications system and a method that allow for compensation of chromatic dispersion and polarization mode dispersion imparted to a communications signal propagating through an optical link. The system is based on a cost-effective optical transport architecture that accommodates baud rates exceeding 15 Gbaud and eliminates the need for costly optical dispersion compensators. Compensation for polarization mode dispersion is performed at the receiver using nonlinear processing. Advantageously, direct detection modulation using inexpensive electro-optic system components can be used in place of more costly and complex coherent and differential modulation formats. Digital filtering can be performed at the transmitter and the input signal can be inverted based on the nonlinearity of the transmitter electro-optic components. Consequently, the bandwidth and linearity requirements for the transmitter electro-optic components are relaxed, and cost reductions are realized.

Abstract: A method of transmitting a data signal in an optical communications system. The method includes processing the data signal to generate an analog drive signal, wherein the processing comprises applying a first non-linear operation such that frequency components of the drive signal lay in at least two separated spectral bands. An optical carrier light is modulated using the analog drive signal.

Abstract: Managing performance of an optical communications network may be facilitated by digital noise loading techniques. The digital noise loading techniques may include measuring a quality of a communication signal received at a coherent optical receiver, applying digital noise to the communication signal at the coherent optical receiver, and detecting a change in the quality of the communication signal at the coherent optical receiver in response to the application of the digital noise. Based on the change in the quality of the communication signal, an operating characteristic and/or a performance margin of the coherent optical receiver may be determined, prompting or facilitating further actions such as adjusting one or more operating parameters of the optical communications network and/or triggering an alert.

Abstract: In a Forward Error Correction (FEC) technique, parity vectors are computed such that: each parity vector spans a set of frames; a subset of bits of each frame is associated with parity bits in each parity vector; and a location of parity bits associated with one frame in one parity vector is different from that of parity bits associated with the frame in another parity vector. Values of decoded hits of a first frame are deduced from known parity bits of a first parity vector having an effective length of one frame. For parity vectors having, an effective length greater than one frame, a Log Likelihood Ratio of each unknown parity bit associated with the first frame is updated based on known and unknown parity bits of each parity valor. The first frame is decoded using the deduced bit values and the updated LLR values.

Abstract: A method, a network element, and a network include determining excess margin relative to margin needed to ensure performance at a nominal guaranteed rate associated with a flexible optical modem configured to communicate over an optical link; causing the flexible optical modem to consume most or all of the excess margin, wherein the capacity increased above the nominally guaranteed rate includes excess capacity; and mapping the excess capacity to one or more logical interfaces for use by a management system, management plane, and/or control plane. The logical interfaces can advantageously be used by the management system, management plane, and/or control plane as one of restoration bandwidths or short-lived bandwidth-on-demand (BOD) connections, such as sub-network connections (SNCs) or label switched paths (LSPs).

Abstract: A method, a network element, and a network include determining excess margin relative to margin needed to insure performance at a nominal guaranteed rate associated with a flexible optical modem configured to communicate over an optical link; causing the flexible optical modem to consume most or all of the excess margin, wherein the capacity increased above the nominal guaranteed rate includes excess capacity; and mapping the excess capacity to one or more logical interfaces for use by a management system, management plane, and/or control plane. The logical interfaces can advantageously be used by the management system, management plane, and/or control plane as one of restoration bandwidth or short-lived bandwidth-on-demand (BOD) connections, such as sub-network connections (SNCs) or label switched paths (LSPs).

Abstract: Managing performance of an optical communications network may be facilitated by digital noise loading techniques. The digital noise loading techniques may include measuring a quality of a communication signal received at a coherent optical receiver, applying digital noise to the communication signal at the coherent optical receiver, and detecting a change in the quality of the communication signal at the coherent optical receiver in response to the application of the digital noise. Based on the change in the quality of the communication signal, an operating characteristic and/or a performance margin of the coherent optical receiver may be determined, prompting or facilitating further actions such as adjusting one or more operating parameters of the optical communications network and/or triggering an alert.

Abstract: A method, a network element, and a network include determining excess margin relative to margin needed to insure performance at a nominal guaranteed rate associated with a flexible optical modem configured to communicate over an optical link; causing the flexible optical modem to consume most or all of the excess margin, wherein the capacity increased above the nominal guaranteed rate includes excess capacity; and mapping the excess capacity to one or more logical interfaces for use by a management system, management plane, and/or control plane. The logical interfaces can advantageously be used by the management system, management plane, and/or control plane as one of restoration bandwidth or short-lived bandwidth-on-demand (BOD) connections, such as sub-network connections (SNCs) or label switched paths (LSPs).

Abstract: Bit-transparent muxing of an input signal for transport through an optical communications network. A fixed length container of the optical communications network is defined, which includes an overhead and a payload. A stuffing ratio (?) is based on a line rate of the input signal and a data rate of the container. A number (NFS) of fixed stuffs is computed based on the stuffing ratio (?). The input signal and NFS fixed stuffs are inserted into the payload of the container, and the computed number NFS stored in the container's overhead. In some embodiments, the container is an overclocked OTU-3 (OTU3+) frame having a line rate of 44.6 Gb/s. This enables bit-transparent mux/demux of four nominal 10-Gig signals having line rates within a range of between 7.6 Gb/s and 10.4 Gb/s, or a single nominal 40-Gig signal having a line rate within a range of between 38.8 Gb/s and 41.6 Gb/s.

Abstract: A transmitter in an optical communications system includes a digital signal processor for processing a data signal to generate a sample stream encoding successive symbols in accordance with a constrained phase modulation scheme having a constellation of at least two symbols and a modulation phase constrained to a phase range spanning less than 4?. A digital-to-analog converter converts the sample stream into a corresponding analog drive signal. A finite range phase modulator modulates a phase of a continuous wavelength channel light in accordance with the analog drive signal, to generate a modulated channel light for transmission through the optical communications system. A receiver in the optical communications system includes an optical stage for detecting phase and amplitude of the modulated channel light and for generating a corresponding sample stream, and a digital signal processor for processing the sample stream to estimate each successive symbol of the modulated channel light.

Abstract: Bit-transparent muxing of an input signal for transport through an optical communications network is disclosed. A stuffing ratio is based on a line rate of the input signal and a data rate of a fixed length container. A number (NFS) of fixed stuffs is computed based on the stuffing ratio. The input signal and NFS fixed stuffs are inserted into the payload of the container, and the computed number of NFS are stored in the container's overhead. In some embodiments, the container is an overclocked OTU-3 (OTU3+) frame having a line rate of 44.6 Gb/s. This enables bit-transparent mux/demux of four nominal 10 Gig signals having line rates within a range of between 7.6 Gb/s and 10.4 Gb/s, or a single nominal 40 Gig signal having a line rate within a range of between 38.8 Gb/s and 41.6 Gb/s.

Abstract: Managing performance of an optical communications network may be facilitated by digital noise loading techniques. The digital noise loading techniques may include measuring a quality of a communication signal received at a coherent optical receiver, applying digital noise to the communication signal at the coherent optical receiver, and detecting a change in the quality of the communication signal at the coherent optical receiver in response to the application of the digital noise. Based on the change in the quality of the communication signal, an operating characteristic and/or a performance margin of the coherent optical receiver may be determined, prompting or facilitating further actions such as adjusting one or more operating parameters of the optical communications network and/or triggering an alert.

Abstract: An optical network and method of protection switching between first and second transceivers where dispersion compensation is effected electrically in the transmitters. The method includes detecting, at the second transceiver, a signal failure of a signal transmitted from the first transceiver and, upon detecting the signal failure, signaling the first transceiver to change its compensation function. The signaling can be done by encoding overhead bits in a signal transmitted from the second to the first transceiver. Another method of protection switching includes both transceivers toggling alternate reception paths upon detecting a signal failure and changing their dispersion compensation function to that of their respective alternate path.

Abstract: A method of transmitting a data signal in an optical communications system. The method includes processing the data signal to generate an analog drive signal, wherein the processing comprises applying a first non-linear operation such that frequency components of the drive signal lay in at least two separated spectral bands. An optical carrier light is modulated using the analog drive signal.

Abstract: A method of protection switching between first and second transceivers where dispersion compensation is effected electrically in the transmitters. The method includes detecting, at the second transceiver, a signal failure of a signal transmitted from the first transceiver and, upon detecting the signal failure, signalling the first transceiver to change its compensation function. The signalling can be done by encoding overhead bits in a signal transmitted from the second to the first transceiver. Another method of protection switching includes both transceivers toggling alternate reception paths upon detecting a signal failure and changing their dispersion compensation function to that of their respective alternate path.

Abstract: A transmitter in an optical communications system includes a digital signal processor for processing a data signal to generate a sample stream encoding successive symbols in accordance with a constrained phase modulation scheme having a constellation of at least two symbols and a modulation phase constrained to a phase range spanning less than 4?. A digital-to-analog converter converts the sample stream into a corresponding analog drive signal. A finite range phase modulator modulates a phase of a continuous wavelength channel light in accordance with the analog drive signal, to generate a modulated channel light for transmission through the optical communications system. A receiver in the optical communications system includes an optical stage for detecting phase and amplitude of the modulated channel light and for generating a corresponding sample stream, and a digital signal processor for processing the sample stream to estimate each successive symbol of the modulated channel light.

Abstract: In a decoder implementing a belief propagation algorithm for iteratively decoding a Low Density Parity Check (LDPC) encoded data block, a method of computing messages to be sent by a first node of the decoder to at least one neighbor node of the decoder. The method comprises: processing messages received by the first node to remove an echo of a previous message sent by the first node to the at least one neighbor node in a previous iteration, to yield corresponding modified messages; computing a message for a current iteration using the modified messages; and broadcasting the computed message for the current iteration to each of the at least one neighbor nodes.

Abstract: In a direct-detection receiver having an analog-to-digital converter (ADC) for sampling a received optical signal and a sequence estimator for recovering data symbols from a multi-bit sample stream generated by the ADC, a method of acquiring a channel lock condition of a clock recovery block of the receiver. A plurality of sets of channel statistics are provided. Each set of channel statistics optimizes performance of the sequence estimator for a respective predetermined combination of channel chromatic dispersion and polarization mode dispersion. At least one set of channel statistics will, when installed in the sequence estimator, yield symbol estimates having residual distortions that are within an acquisition range of the clock recovery block. During start-up of the receiver, one of the sets of channel statistics is selected and installed in the Sequence Estimator.

Abstract: Methods and techniques are disclosed for correcting the effect of cycle slips in a coherent communications system. A signal comprising SYNC bursts having a predetermined periodicity and a plurality of known symbols at predetermined locations between successive SYNC bursts is received. The received signal is partitioned into data blocks. Each data block encompasses at least data symbols and a set of check symbols corresponding to the plurality of known symbols at predetermined locations between a respective pair of successive SYNC bursts in the signal. Each data block is processed to detect a cycle slip. When a cycle slip is detected, the set of check symbols of the data block are examined to identify a first slipped check symbol, and a phase correction applied to data symbols of the data block lying between the first slipped check symbol and an end of the data block.