Abstract: Consistent with an aspect of the present disclosure, optical signals are transmitted that are modulated in accordance with an 8QAM modulation format. The optical signals carry symbols of data and may be represented by a constellation in the IQ plane that includes four inner points that are symmetrically arranged about the origin, and four outer points that are uniformly distributed about the origin, but rotated relative to the inner points. The rotation is toward inner points that represent symbols for which an erroneous transition between the outer points and such inner points is more likely to result in a single bit error, instead of two bit errors, because the symbol corresponding to the outer point and the symbol corresponding to such inner point differ by just one bit. Accordingly, a binary forward error correction algorithm may be employed to correct the errored bit.

Abstract: Consistent with the present disclosure, data, in digital form, is received by a transmit node of an optical communication system, and converted to an analog signal by a digital-to-analog converter (DAC) to drive a modulator. The modulator, in turn, modulates light at one of a plurality of wavelengths in accordance with the received data forming a plurality of corresponding carriers. The carriers are modulated according to one of a plurality of modulation formats and then optically combined to form a superchannel of a constant maximum capacity, for example. Accordingly, the number of carriers and the bit rate for each carrier remain constant for each modulation format to realize a constant maximum capacity. The superchannel is then transmitted over an optical communication path to a receive node. At the receive node, the superchannel is optically demultiplexed from a plurality of other superchannels.

Abstract: Consistent with an aspect of the present disclosure, optical signals are transmitted that are modulated in accordance with an 8QAM modulation format. The optical signals carry symbols of data and may be represented by a constellation in the IQ plane that includes four inner points that are symmetrically arranged about the origin, and four outer points that are uniformly distributed about the origin, but rotated relative to the inner points. The rotation is toward inner points that represent symbols for which an erroneous transition between the outer points and such inner points is more likely to result in a single bit error, instead of two bit errors, because the symbol corresponding to the outer point and the symbol corresponding to such inner point differ by just one bit. Accordingly, a binary forward error correction algorithm may be employed to correct the errored bit.

Abstract: Various apparatus and methods may use iterative de-mapping/decoding to on received symbol estimates corresponding to interleaved coded modulation (ICM) using low-density parity check convolutional coding (LPDC-CC). The iterative de-mapping/decoding, may take the form of a multi-stage feed-forward arrangement that may include multiple identically designed stages, and the stages may use parallelism to increase speed and efficiency.

Abstract: Consistent with the present disclosure, an optical communication system is provided in which data is carried over optical signals including subcarriers. The subcarriers may be modulated with the standard modulation formats noted above, but the modulation formats are selectively assigned to the subcarriers, such that some subcarriers are modulated with different standard modulation formats than others. As used herein, a “standard modulation format” is one of BPSK, and n-QAM, where n is an integer greater than one. Such n-QAM modulation formats include of 3-QAM, 4-QAM (QPSK), 8-QAM, 16-QAM, 64-QAM, 128-QAM, and 256-QAM. By selecting the number of subcarriers and the types of modulation formats employed, an optical signal with an effective SE that is between that of the standard modulation formats can be generated for transmission over a distances that more closely matches the link distance.

Abstract: An optical modulator includes a splitter, phase modulators, amplitude modulators, intensity modulators, and a combiner. The splitter is configured to receive light, and split the light into portions of the light. Each of the phase modulators is configured to receive a corresponding one of the portions of the light, and modulate a phase of the portion of the light to provide a phase-modulated signal. Each of the amplitude modulators is configured to receive a corresponding one of the phase-modulated signals, and modulate an amplitude of the phase-modulated signal to provide an amplitude-modulated signal. Each of the intensity modulators is configured to receive a corresponding one of the amplitude-modulated signals, and modulate an intensity of the amplitude-modulated signals to provide an intensity-modulated signal. The combiner is configured to receive the intensity-modulated signals, combine the intensity-modulated signals into a combined signal, and output the combined signal.

Abstract: A system receives four-bit symbols that correspond to traffic associated with a three-bit phase modulation scheme and are encoded based on a four-bit phase modulation scheme. The system determines values with which to perform equalization that enable the four-bit symbols to be restored to a condition that existed prior to being transmitted to the system. The system performs, using the values, equalization on a four-bit symbol that includes at least a first pair of bits associated with a first polarization, and performs, after completing the equalization, another equalization on another four-bit symbol that includes at least a second pair of bits associated with a second polarization. The system identifies a three-bit symbol, of a set of three-bit symbols associated with the three-bit phase modulation scheme, based on the equalized first pair of bits and the equalized second pair of bits, generates the three-bit symbol, and outputs the three-bit symbol.

Abstract: In one implementation, a device may include a voltage regulator circuit, a data processing circuit, and an error correction circuit, where the error correction circuit may correct errors in data processed by the data processing circuit to obtain error-corrected data and output an error-corrected version of the processed data. Additionally, an error monitor circuit may output an error signal indicative of a level of the errors in the processed data. A control circuit may receive the error signal and control the voltage regulator circuit to adjust, based on the error signal, the supply voltage to the data processing circuit. In some implementations, the control circuit may also base its decision to control the voltage regulator circuit based on available timing margins in the data processing circuit.

Abstract: Consistent with an aspect of the present disclosure, an optical signal carrying data or information is supplied to photodetector circuitry that generates a corresponding analog signal. The analog signal may be amplified or otherwise processed and supplied to analog-to-digital conversion (ADC) circuitry, which samples the analog signal to provide a plurality of digital signals or samples. The timing of such sampling is in accordance with a clock signal supplied to the ADC circuitry. A phase detector is provided that detects and adjust the clock signal to have a desired phase based on frequency domain data that is output from a Fast Fourier transform (FFT) circuit that receives the digital samples. Preferably, the phase detector circuit is configured such that it need not receive all the frequency domain data output from the FFT at any given time in order to determine the clock phase.

Abstract: An optical system may have an optical transmitter including a digital signal processor to receive a signal channel, add data corresponding to a pilot tone, generate a digital signal associated with the signal channel and including the pilot tone, and output the digital signal. The optical system may further have a digital-to-analog converter to convert the digital signal to an analog signal, a laser to provide an optical signal, and a modulator to receive the optical signal and the analog signal, and modulate the optical signal based on the analog signal to form a modulated optical signal. The modulated optical signal may include the pilot tone. The optical system may also have an optical receiver to receive the modulated optical signal, process the modulated optical signal to determine a phase associated with the pilot tone, and apply the phase to the modulated optical signal to recover the signal channel.

Abstract: A system is configured to receive a block of symbols, associated with a phase-modulated signal that includes data symbols that correspond to a payload associated with the signal, and control symbols; process the control symbols to identify an amount of phase noise associated with the control symbols; reset a phase, associated with each of the data symbols, based on the amount of phase noise and a reference phase; interleave the respective data samples, of each of the data symbols with other data samples, where the interleaved respective data samples cause errors, associated with the respective data samples, to be spread out among the other data samples and reduces an error rate relative to a prior data rate that existed before the interleaving; and perform forward error correction on the interleaved respective data samples.

Abstract: A system receives traffic that includes four-bit symbols, the four-bit symbols being encoded using a four-bit phase modulation scheme; and processes the traffic to recover a four-bit symbol. The system also decodes the recovered four-bit symbol to obtain a three-bit symbol. The three-bit symbol is associated with a three-quadrature amplitude modulation (3QAM) scheme, and the decoding is performed without creating an error, within the traffic, when cycle slip occurs. The system outputs the traffic based on the three-bit symbol.

Abstract: Consistent with the present disclosure, optical signals are modulated in accordance with a higher order QAM modulation format, such as 8-QAM, to carry customer data, for example. The optical signals are converted to corresponding electrical signals, which are then subject to further processing. In particular, phase data associated with the higher order QAM constellation is processed, such that the outer points of the constellation are rotated to have the same phase as the inner points. As a result, both the inner and outer points resemble a constellation, and both may be more readily processed using feedforward or feedback carrier recovery. After such carrier recovery, the phase data is further processed so that the outer points are rotated back and the customer data can be extracted from the phase data.

Abstract: Consistent with the present disclosure, a method and system for detecting a clock phase of an optical signal in a coherent receiver is provided that is insensitive to polarization mode dispersion (PMD) and other polarization effects in the optical communication system. The clock phase of the received signal is estimated by first calculating a phase shift between a pair of related frequency domain data outputs of a Fourier transform circuit. The calculated phase shift includes a phase component and a data spectrum component. The calculated phase shift is then averaged over a number of clock cycles to remove the data spectrum components thus enabling extraction of the phase component. A determinant function on the time averaged result is used to normalize any effects of PMD from the received signal and isolate the phase component. In this manner, the phase component is not dependent on the PMD effects in the optical communication system.

Abstract: An optical system may have an optical transmitter including a digital signal processor to receive a signal channel, add data corresponding to a pilot tone, generate a digital signal associated with the signal channel and including the pilot tone, and output the digital signal. The optical system may further have a digital-to-analog converter to convert the digital signal to an analog signal, a laser to provide an optical signal, and a modulator to receive the optical signal and the analog signal, and modulate the optical signal based on the analog signal to form a modulated optical signal. The modulated optical signal may include the pilot tone. The optical system may also have an optical receiver to receive the modulated optical signal, process the modulated optical signal to determine a phase associated with the pilot tone, and apply the phase to the modulated optical signal to recover the signal channel.

Abstract: Consistent with the present disclosure, a method and system for estimating chromatic dispersion of an optical signal in a coherent receiver is provided that is insensitive to polarization mode dispersion (PMD) and other polarization effects in the optical communication system. The effects of chromatic dispersion in the optical system are estimated by first calculating a phase shift between a pair of related frequency domain data outputs of a Fourier transform circuit. The calculated phase shift includes a linear phase component that is proportional to the chromatic dispersion, a DC constant phase component, and a data spectrum component. The calculated phase shift is then averaged over a number of clock cycles to remove the data spectrum components. The time averaged result is used to normalize any effects of PMD from the received signal. A slope of the linear phase component as a function of frequency is then calculated and used to estimate the value for chromatic dispersion.

Abstract: A system receives a first word on which to perform error correction; identifies combinations in which encoded bits, within the first word, can be inverted; generates candidate words based on the first word and the combinations; decodes the candidate words; determines distances between the decoded words and the first word; selects, as a second word, one of the decoded words associated with a shortest distance; compares the second word to the first word to identify errors within the first word; generates a value to cause a reliability level of the first word to increase when a quantity of the errors is less than a threshold; generates another value to cause a reliability level of the first word to decrease when the quantity of the errors is not less than the threshold; and outputs a third word based on the first word, and the value or the other value.

Abstract: A system is configured to receive a word that includes a group of samples; randomly select a subset of the samples; identify first samples, from the subset, with a lowest level of reliability; select another subset of the samples; identify second samples, from the other subset, with a lowest level of reliability; and create a merged subset based on selected first samples and selected second samples. The system is also configured to select a further subset of the samples; identify third samples, from the further subset, with a lowest level of reliability; identify fourth samples, from the merged subset, associated with a lowest level of reliability; create another merged subset based on a greater probability that fourth samples than third samples are included in the other merged subset; and generate another word based a sample from the other merged subset; and process the word using the other word.

Abstract: A system receives traffic that includes four-bit symbols, the four-bit symbols being encoded using a four-bit phase modulation scheme; and processes the traffic to recover a four-bit symbol. The system also decodes the recovered four-bit symbol to obtain a three-bit symbol. The three-bit symbol is associated with a three-quadrature amplitude modulation (3QAM) scheme, and the decoding is performed without creating an error, within the traffic, when cycle slip occurs. The system outputs the traffic based on the three-bit symbol.

Abstract: A system receives four-bit symbols that correspond to traffic associated with a three-bit phase modulation scheme and are encoded based on a four-bit phase modulation scheme. The system determines values with which to perform equalization that enable the four-bit symbols to be restored to a condition that existed prior to being transmitted to the system. The system performs, using the values, equalization on a four-bit symbol that includes at least a first pair of bits associated with a first polarization, and performs, after completing the equalization, another equalization on another four-bit symbol that includes at least a second pair of bits associated with a second polarization. The system identifies a three-bit symbol, of a set of three-bit symbols associated with the three-bit phase modulation scheme, based on the equalized first pair of bits and the equalized second pair of bits, generates the three-bit symbol, and outputs the three-bit symbol.