Abstract: A digital signal processor (DSP), may identify symbol values associated with a 5 quadrature amplitude modulation (5QAM) signal. The DSP may determine a first bit set based on the symbol values and a first particular bit value. The DSP may determine a second bit set based on the symbol values and a second particular bit value. The DSP may compute a first distance based on the first bit set and the symbol values. The DSP may compute a second distance based on the second bit set and the symbol values. The DSP may determine that the first distance is less than the second distance. The first distance being less than the second distance may indicate that the first bit set is a correctly decoded bit set. The DSP may provide an output associated with the correctly decoded bit set.

Abstract: An optical receiver receives an optical signal with a phase error and pilot symbols, and converts the optical signal into an electrical signal. The optical receiver identifies, based on the pilot symbols, a cycle slip due to the phase error and associated with a transition time. The optical receiver determines, based on the pilot symbols, a direction and a center of the cycle slip, and generates a rotation value based on the direction and the center. The optical receiver applies the rotation value to minimize the phase error in the electrical signal except for phase error associated with the transition time and to generate a modified electrical signal. The optical receiver generates an erase signal based on the transition time and the center of the cycle slip, and uses the erase signal to minimize an effect of the phase error associated with the transition time of the cycle slip.

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 include a digital signal processor (DSP) to receive first samples of a digital signal. The first samples may be Hamming encoded. The DSP may correlate the first samples to multiple groups of second samples to determine multiple correlation values. Each of the multiple groups of second samples may correspond to respective code words. Each of the multiple correlation values may correspond to a correlation measurement between the first samples and each of the multiple groups of second samples. The DSP may determine a particular code word, of the multiple code words, corresponding to one of the correlation values of the multiple correlation values; determine output bits based on bits of the particular code word and the one of the correlation values; and provide the output bits. The output bits may include data associated with the digital signal.

Abstract: A digital signal processor (DSP) may receive samples of a signal from an analog-to-digital converter (ADC); convert the samples from a time domain to a frequency domain; determine a clock phase error of the samples while in the frequency domain; and provide a voltage corresponding to the clock phase error. The voltage may be provided to reduce timing errors associated with the samples.

Abstract: An apparatus including a photodiode, a low pass filter, an analog-to-digital converter, an interpolation circuit and a digital signal processor is disclosed. The photodiode receives a portion of a plurality of optical signals, each of which is modulated in accordance with a corresponding one of a plurality of data streams, and each having a corresponding one of a plurality of wavelengths. The photodiode supplies an electrical output. The low-pass filter supplies a filtered output in response to the electrical output. The analog-to-digital converter is configured to sample the filtered output at a first sampling rate to generate a plurality of first data samples. The interpolation circuit is configured to receive the plurality of first data samples and supply a plurality of second data samples at a second sampling rate less the first sampling rate. The digital signal processor circuit is configured to receive the plurality of second data samples.

Abstract: An optical transmitter may include an optical source to provide a first optical signal having a varying frequency; an optical circuit to receive a portion of the first optical signal and provide a second optical signal corresponding to a change in frequency of the first optical signal; a photodetector to receive the first optical signal and provide an electrical signal that is indicative of the change in frequency of the first optical signal; an integrator to receive the electrical signal and provide an inverted electrical signal; and a controller to process the inverted electrical signal and provide a current, associated with the inverted electrical signal, to the optical source. The optical source may reduce the phase noise associated with the first optical signal based on the current.

Abstract: An optical system may include an optical transmitter or an optical receiver. The optical transmitter may include a laser to provide an input signal, a first digital signal processor (DSP) to receive a data signal, provide non-rotated and rotated symbols corresponding to the data signal, and provide digital signals corresponding to the non-rotated and the rotated symbols to cause one or more digital to analog converts to convert the digital signals to analog signals. The optical transmitter may further provide a modified 5 quadrature amplitude modulation (5QAM) signal based on the analog signals and the input signal. A constellation map of the modified 5QAM signal may include all constellation points of a 16QAM signal. The optical receiver may include a second DSP to receive components associated with the 5QAM signal, filter the components, reduce phase noise of the 5QAM signal, and provide data associated with the 5QAM signal.

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, data, in digital form, is received by a transmit nodes of an optical communication, and converted to 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. The modulated light is then transmitted over an optical communication path to a receive node. At the receive node, the modulated optical signal, as well as other modulated optical signals are supplied to a photodetector circuit, which receives additional light at one of the optical signal wavelengths from a local oscillator laser. An analog-to-digital converter (ADC) is provided in the receive node to convert the electrical signals output from the photodetector into digital form. The output from the ADC is then filtered in the electrical domain, such that optical demultiplexing of individual channels is unnecessary.

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: 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, data, in digital form, is received by a transmit nodes of an optical communication, and converted to 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. The modulated light is then transmitted over an optical communication path to a receive node. At the receive node, the modulated optical signal, as well as other modulated optical signals are supplied to a photodetector circuit, which receives additional light at one of the optical signal wavelengths from a local oscillator laser. An analog-to-digital converter (ADC) is provided in the receive node to convert the electrical signals output from the photodetector into digital form. The output from the ADC is then filtered in the electrical domain, such that optical demultiplexing of individual channels is unnecessary.

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: An optical system includes a transmitter module and/or a receiver module. The transmitter module is configured to receive input data, map the input data to a set of subcarriers associated with an optical communication channel, independently apply spectral shaping to each of the subcarriers, generate input values based on the spectral shaping of each of the subcarriers, generate voltage signals based on the input values, modulate light based on the voltage signals to generate an output optical signal that includes the subcarriers, and output the output optical signal. The receiver module is configured to receive the output optical signal, convert the output optical signal to a set of voltage signals, generate digital samples based on the set of voltage signals, independently process the digital samples for each of the subcarriers, map the processed digital samples to produce output data, and output the output data.

Abstract: Consistent with the present disclosure, data, in digital form, is received by a transmit nodes of an optical communication, and converted to 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. The modulated light is then transmitted over an optical communication path to a receive node. At the receive node, the modulated optical signal, as well as other modulated optical signals are supplied to a photodetector circuit, which receives additional light at one of the optical signal wavelengths from a local oscillator laser. An analog-to-digital converter (ADC) is provided in the receive node to convert the electrical signals output from the photodetector into digital form. The output from the ADC is then filtered in the electrical domain, such that optical demultiplexing of individual channels is unnecessary.

Abstract: Consistent with the present disclosure, data, in digital form, is received by a transmit nodes of an optical communication, and converted to 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. The modulated light is then transmitted over an optical communication path to a receive node. At the receive node, the modulated optical signal, as well as other modulated optical signals are supplied to a photodetector circuit, which receives additional light at one of the optical signal wavelengths from a local oscillator laser. An analog-to-digital converter (ADC) is provided in the receive node to convert the electrical signals output from the photodetector into digital form. The output from the ADC is then filtered in the electrical domain, such that optical demultiplexing of individual channels is unnecessary.

Abstract: An optical system may include a polarization beam splitter having an input that receives multiple optical signals, a first output and a second output. The first output may provide components of the multiple optical signals having a first polarization. The second output may provide components of the multiple optical signals having a second polarization. The optical system may include a rotator having an input that receives the components to rotate the first polarization such that each of the components has the second polarization, and an output to supply components as rotated components. The optical system may also include an optical circuit including a substrate. The rotator may be separate from the substrate. The optical circuit may include an optical demultiplexer circuit provided on the substrate to receive the rotated components and the components.

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.