Abstract: Client data bits, including first client data bits and second client data bits, are communicated from a transmitter to a receiver. At the transmitter, the first client data bits are processed to generate processed values, where each processed value is more likely to be a first element than a second element. Forward Error Correction ‘FEC’ encoding is applied to the second client data bits to generate FEC-encoded values. Symbols are created by mapping the FEC-encoded values to first positions in the symbols and by mapping the processed values to second positions in the symbols. The symbols are modulated onto a communications channel using a modulation scheme with a code that assigns a lower average energy to symbols containing the first elements in the second positions than to symbols containing the second elements in the second positions. At the receiver, client data bits are decoded using conditional chain decoding.

Abstract: 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.

Abstract: Compression coding techniques are proposed for use with forward error correction (FEC) coding, which may provide higher information rates by reducing the proportion of redundant bits relative to information bits that are transmitted from a transmitter to a receiver. In one example, the transmitter calculates a plurality of determiners from a set of information bits, where each determiner is calculated as a first function of a respective first subset of the information bits. The transmitter then calculates a nub as a second function of the plurality of determiners, where the nub comprises a number of redundant bits that is less than a number of bits comprised in the plurality of determiners. The set of information bits is transmitted to the receiver in a first manner, and the nub is transmitted to the receiver in a second manner, where the first manner may be distinct from the second manner.

Abstract: In a communications system having an analog channel configured to convey a data signal from a transmitter to a receiver, a method of mitigating narrow-band impairment imposed by the analog channel on the data signal within a bounded spectral region of a spectrum of the data signal. A transmitter digital signal processor (Tx DSP) applying a first adaptation function to the data signal prior to transmitting the data signal through the analog channel. A receiver digital signal processor (Rx DSP) applying a second adaptation function to the data signal received through the analog channel. The first and second adaptation functions are selected to cooperatively mitigate effects of the narrow-band impairment imposed by the analog channel.

Abstract: In data communications, a suitably designed contrast coding scheme, comprising a process of contrast encoding at a transmitter end and a process of contrast decoding at a receiver end, may be used to adjust the contrast in bit error rate (BER) experienced by different classes of bits. Contrast coding may be used to tune the BERs experienced by different subsets of bits, relative to each other, to better match a plurality of forward error correction (FEC) schemes used for transmission of information bits, which may ultimately provide a communications system having a higher noise tolerance, or greater data capacity, or smaller size, or lower heat.

Abstract: Aspects of the present invention provide techniques for compensating nonlinear impairments of a signal traversing an optical communications system. A parallel array of linear convolutional filters are configured to process a selected set of samples of the signal to generate an estimate of a nonlinear interference field. The predetermined set of samples comprises a first sample and a plurality of second samples. A processor applies the estimated nonlinear interference field to the first sample to least partially compensate the nonlinear impairment.

Abstract: 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.

Abstract: A transmitter comprises a complex mixer to generate a single I analog drive signal and a single Q analog drive signal, and a single multi-dimensional optical modulator configured to modulate an optical carrier light using the single I analog drive signal and the single Q analog drive signal to produce a modulated optical signal for transmission. Alternatively, a transmitter comprises a complex mixer to generate two I analog drive signals and two Q analog drive signals, and a single multi-dimensional multiple-electrode optical modulator configured to modulate an optical carrier light using the analog drive signals to produce a modulated optical signal for transmission. In both transmitters, the optical carrier light is produced by a single laser, and frequency components of the first data signal are located in a different portion of a spectrum of the modulated optical signal than frequency components of the second data signal.

Abstract: Forward Error Correction technique: parity vectors are computed such that each parity vector spans multiple FEC frames; in a given FEC frame, a first set of syndrome bits are due to the parity vectors, and a second set of syndrome bits satisfy FEC equations that involve bits of the given FEC frame including the first set of syndrome bits; and the parity vectors are staggered with respect to any sequence in which the FEC frames are processed. Values of decoded bits of a first frame are deduced from known 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 bit associated with the first frame is updated based on known and unknown bits of each parity vector. First frame is decoded using deduced bit values and updated LLR values.

Abstract: A received signal is received over a noise channel. A stream of received symbols is recovered from the received signal. Each symbol is decoded into one or more bits, where a decoded bit of the symbol has a high probability of being in error, and a probability of being a ‘1’ substantially different from 0.5. An inverse mapping is performed on the decoded bits, where the output of the inverse mapping is a stream of bits with a very low probability of being in error and a probability of being a ‘1’ substantially equal to 0.5.

Abstract: A method of transmitting a data signal using an optical transmitter of an optical communications system. The optical transmitter is configured to modulate an optical carrier in successive signalling intervals to generate an optical signal. A modulation scheme is provided which comprises a multi-dimensional symbol constellation. The modulation scheme is designed such that an average degree of polarization of a modulated optical signal output from the optical transmitter has a first value when averaged across a first signalling interval, and has a second value when averaged across more than one and fewer than 100 signalling intervals. The second value is less than 10 percent of the first value. During run-time, an encoder of the optical transmitter encoding a data signal to be transmitted as symbols of the constellation, and a modulator of the optical transmitter modulating available dimensions of the optical carrier in accordance with the symbols.

Abstract: 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.

Abstract: Techniques for transmitting a data signal through an optical communications system. An encoder is configured to encode the data signal to generate symbols to be modulated onto an optical carrier. Each symbol encodes multiple bits of data and includes a first portion selected from a first constellation and a second portion selected from a second constellation. The first and second constellations have respective different average amplitudes. Each of the first and second constellations have a cardinality of at least two and the cardinality of the first constellation is greater than the cardinality of the second constellation. A modulator is configured to modulate a first frame of the optical signal using the first portion and modulate a second frame of the optical signal using the second portion. A selection of one frame of the optical signal to be used as the first frame encodes at least 1 bit of data.

Abstract: A method of transmitting a data signal using an optical transmitter of an optical communications system. A first encoder processes an N-bit input vector in accordance with a first mapping to generate a corresponding M-bit data stream. A Forward Error Correction encoder processes the M-bit data stream in accordance with a predetermined FEC encoding scheme to generate an encoded signal. A constellation mapper maps the encoded signal to symbol values in accordance with a predetermined modulation scheme to generate a corresponding symbol stream. A modulator modulates a carrier light in accordance with the encoded symbol stream to generate an optical signal for transmission through the optical communications system. The first mapping can be adjusted to maximize performance of the optical communications system.

Abstract: A receiver of an optical communications system includes a set of two or more analog-to digital A/D converters, a respective transform block connected to an output of each A/D converter, and a summation block. Each A/D converter samples a respective low-bandwidth analog signal comprising a respective portion of a high-bandwidth data signal. Each transform block calculates a set of spectral components of the respective low-bandwidth analog signal. The summation block combines respective spectral components calculated by each transform block to construct spectral terms of a combined signal having a spectrum corresponding to that of the high-bandwidth data signal.

Abstract: In a coherent receiver of an optical communication system, a method of processing a detected symbol estimate to determine a most likely value of a corresponding transmitted data word, the transmitted data word comprising one or more data bits encoded in a transmitter using a predetermined constellation of at least two symbols. A set of two or more virtual constellation points are define in a decision region corresponding to a possible value of the data word. The detected symbol estimate is processed to find a most likely virtual constellation point given the detected symbol estimate. The most likely value of the corresponding transmitted data word is determined based on the most likely virtual constellation point.

Abstract: Forward Error Correction technique: parity vectors are computed such that each parity vector spans multiple FEC frames; in a given FEC frame, a first set of syndrome bits are due to the parity vectors, and a second set of syndrome bits satisfy FEC equations that involve bits of the given FEC frame including the first set of syndrome bits; and the parity vectors are staggered with respect to any sequence in which the FEC frames are processed. Values of decoded bits of a first frame are deduced from known 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 bit associated with the first frame is updated based on known and unknown bits of each parity vector. First frame is decoded using deduced bit values and updated LLR values.

Abstract: A method of data symbol recovery. An optical signal is modulated by a transmitter using a modulation scheme comprising a symbol constellation having a predetermined asymmetry and detected at a receiver. Phase error estimates corresponding to data symbol estimates detected from the received optical signal are calculated. A phase rotation is calculated based on the phase error estimates, using a filter function, and the phase rotation applied to at least one data symbol estimate to generate a corresponding rotated symbol estimate. The phase error estimates model the asymmetry of the symbol constellation, such that the computed phase rotation can compensate phase noise that is greater than one decision region of the symbol constellation.

Abstract: A transmitter comprises a complex mixer to generate a single I analog drive signal and a single Q analog drive signal, and a single multi-dimensional optical modulator configured to modulate an optical carrier light using the single I analog drive signal and the single Q analog drive signal to produce a modulated optical signal for transmission. Alternatively, a transmitter comprises a complex mixer to generate two I analog drive signals and two Q analog drive signals, and a single multi-dimensional multiple-electrode optical modulator configured to modulate an optical carrier light using the analog drive signals to produce a modulated optical signal for transmission. In both transmitters, the optical carrier light is produced by a single laser, and frequency components of the first data signal are located in a different portion of a spectrum of the modulated optical signal than frequency components of the second data signal.

Abstract: In a communications system having an analog channel configured to convey a data signal from a transmitter to a receiver, a method of mitigating narrow-band impairment imposed by the analog channel on the data signal within a bounded spectral region of a spectrum of the data signal. A transmitter digital signal processor (Tx DSP) applying a first adaptation function to the data signal prior to transmitting the data signal through the analog channel. A receiver digital signal processor (Rx DSP) applying a second adaptation function to the data signal received through the analog channel. The first and second adaptation functions are selected to cooperatively mitigate effects of the narrow-band impairment imposed by the analog channel.