Abstract: In an Optical Add-Drop Multiplexer, a drop section comprises a Wavelength Selective Switch (WSS) having at least one drop-port, the WSS being operative to couple a respective set of w (where w>1) wavelength channels from a received Wavelength Division Multiplexed (WDM) signal to each drop port. A respective 1:s power splitter is associated with each drop port. Each power splitter supplies the respective set of channels received from its drop port to each one of a corresponding set of coherent receivers. Each coherent receiver operates to receive a selected one of the respective set of channels.

Abstract: A method of recovering a value of a symbol received through an optical communications system. A multi-bit estimate of the symbol is subdivided into a first part and a second part, each part including at least one respective bit of the estimate. A most likely value of the first part is detected. The most likely value of the first part is processed using a Forward Error Correction (FEC) decoder to generate a corrected first part value, which is used to detect a most likely value of the second part. The most likely value of the second part is then processed by the FEC decoder to generate a corrected second part, which is combined with the corrected first part to recover the value of the symbol.

Abstract: Methods and systems of data symbol recovery in a coherent optical receiver of an optical communications system. A respective probabilistic phase error is calculated for each of a plurality of data symbol estimates. A phase rotation is calculated based on the probabilistic 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. Each rotated symbol estimate is processed to generate corresponding decision values of each data symbol.

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 method and system for a estimating a most likely location of a periodic SYNC burst within an optical signal received through an optical communications system. A cross-correlation is calculated between a multi-bit digital signal derived from the optical signal and a known symbol sequence of the SYNC burst. The cross-correlation is processed in at least one sub-block to identify a candidate sub-block in which the SYNC burst is most likely located. The candidate sub-block is then further analyzed to estimate a location of the SYCN burst.

Abstract: A frequency decimation block for processing an analog input signal including a high-bandwidth data signal to generate a parallel set of parallel output signals, in which each output signal represents a respective portion of the high-bandwidth data signal. A preamplifier is provided for amplifying the input signal. A frequency domain divider divides the amplified input signal to generate a set of frequency band signals including a low frequency band signal, a mid-frequency band signal, and a high frequency band signal. Each frequency band signal is supplied to at least one signal path. A respective non-linear processor is connected in each of M signal paths processes the input signal using a respective branch signal to yield a corresponding composite signal. A respective Low-Pass Filter (LPF) is connected in each signal path, for low-pass filtering at least the composite signals to generate corresponding ones of the parallel output signals.

Abstract: In a coherent optical receiver of an optical communications system, methods and systems for receiving a data signal x(t) modulated on an optical signal. A linearly polarized LO light is generated, which has a frequency of f1=f0±?f, where f0 is a frequency of a narrowband carrier of the optical signal, and ?f corresponds with a band-width fB of the data signal x(t). The LO light and a received light of the optical signal are heterodyned on a photodetector. An analog signal generated by the photodetector is low-pass filtered to generate a filtered signal, using a filter characteristic having a sharp cut-off at a frequency of ?f+nfB, where n is an integer multiple. An analog-to digital (A/D) converter samples the filtered signal at a sample rate of 2(?f+nfB) to generate a corresponding multi-bit digital sample stream. The multi-bit digital sample stream is digitally processed to recover respective In-Phase and Quadrature components of the received light of the optical signal.

Abstract: In a coherent optical receiver receiving a polarization multiplexed optical signal through an optical communications network, a method of compensating noise due to polarization dependent loss (PDL). A Least Mean Squares (LMS) compensation block processes sample streams of the received optical signal to generate symbol estimates of symbols modulated onto each transmitted polarization of the optical signal. A decorrelation block de-correlates noise in the respective symbol estimates of each transmitted polarization and generating a set of decorrelated coordinate signals. A maximum likelihood estimator soft decodes the de-correlated coordinate signals generated by the decorrelation block.

Abstract: Phase nonlinearities of an optical communications system are monitored by generating a test signal which includes a predetermined property that is uniquely associated with at least one phase nonlinearity of the optical communications system. The predetermined property of the test signal is then detected at a monitoring point of the optical communications system, and used to estimate the associated phase nonlinearity.

Abstract: A coherent optical receiver Includes an electro-optic module coupled to an electronic signal processing Integrated circuit (IC) via a parallel analog transmission line bus. The electro-optic module receives and detects an optical channel light including a high-bandwidth signal modulated thereon. The electro-optic module includes: a single optical hybrid for mixing the optical channel light with a corresponding continuous wave local oscillator light to generate a mixed light containing the high-bandwidth data signal, at least one photodetector; and an analog frequency decimator for generating a set of parallel analog signals, each analog signal representing a respective portion of the high-bandwidth signal.

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 high-speed signal generator. A digital signal processing (DSP) block generates a set of N (where N is an integer and N?2) parallel digital sub-band signals, each digital sub-band signal having frequency components within a spectral range between 0 Hz and ±Fs/2, where Fs is a sample rate of the digital sub-band signals. A respective Digital-to-Analog Converter (DAC) processes each digital sub-band signal to generate a corresponding analog sub-band signal, each DAC having a sample rate of Fs/2. A combiner combines the analog sub-band signals to generate an output analog signal having frequency components within a spectral range between 0 Hz and ±NFs/2.

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: In a coherent optical receiver receiving a polarization multiplexed optical signal through an optical communications network, a method of compensating noise due to polarization dependent loss (PDL). A Least Mean Squares (LMS) compensation block processes sample streams of the received optical signal to generate symbol estimates of symbols modulated onto each transmitted polarization of the optical signal. A decorrelation block de-correlates noise in the respective symbol estimates of each transmitted polarization and generating a set of decorrelated coordinate signals. A maximum likelihood estimator soft decodes the de-correlated coordinate signals generated by the decorrelation block.

Abstract: A high-speed signal generator. A digital signal processing (DSP) block generates a set of N (where N is an integer and N?2) parallel digital sub-band signals, each digital sub-band signal having frequency components within a spectral range between 0 Hz and ±Fs/2, where Fs is a sample rate of the digital sub-band signals. A respective Digital-to-Analog Converter (DAC) processes each digital sub-band signal to generate a corresponding analog sub-band signal, each DAC having a sample rate of Fs/2. A combiner combines the analog sub-band signals to generate an output analog signal having frequency components within a spectral range between 0 Hz and ±NFs/2.

Abstract: Link bandwidth is varied based on the subscriber traffic load. Varying the link bandwidth has the effect of varying the actual noise margin of the link (in an inverse elation), so that the noise margin will vary inversely with the traffic load. A beneficial result is that, because the noise margin is increased during “off-peak” traffic periods, rapidly varying and burst impairments can be absorbed without causing data loss. In effect, the respective probability distributions of error bursts and traffic load are separated. Data loss only becomes a significant risk when peaks in both distributions coincide. However, the probability of that event occurring is comparatively low. This enables a lower noise margin allocation during design of the link, which dramatically reduces the link cost.

Abstract: Phase nonlinearities of an optical communications system are monitored by generating a test signal which includes a predetermined property that is uniquely associated with at least one phase nonlinearity of the optical communications system. The predetermined property of the test signal is then detected at a monitoring point of the optical communications system, and used to estimate the associated phase nonlinearity.

Abstract: A method and system for a estimating a most likely location of a periodic SYNC burst within an optical signal received through an optical communications system. A cross-correlation is calculated between a multi-bit digital signal derived from the optical signal and a known symbol sequence of the SYNC burst. The cross-correlation is processed in at least one sub-block to identify a candidate sub-block in which the SYNC burst is most likely located. The candidate sub-block is then further analysed to estimate a location of the SYCN burst.

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: A method of forward error correction in an optical communications system. A signal to be transmitted is logically defined as a super-frame comprising a plurality of frames including a parity frame and a predetermined set of data frames. Each frame of the super-frame is processed in accordance with a first FEC scheme having a known error correlation characteristic. At least the set of data frames is processed in accordance with a second FEC scheme which is selected based on the error correlation characteristic of the first FEC scheme.