Abstract: Generation of data streams for two dimensions comprises compensation for a nonideal response of a signal path in an optical communications signal. The data streams are converted to analog electrical signals which drive two dimensions of an electrical-to-optical converter. Output of the electrical-to-optical converter is coupled through an optical link to an optical-to-electrical converter.

Abstract: Generation of data streams for two dimensions comprises compensation for a nonideal response of a signal path in an optical communications signal. The data streams are converted to analog electrical signals which drive two dimensions of an electrical-to-optical converter. Output of the electrical-to-optical converter is coupled through an optical link to an optical-to-electrical converter.

Abstract: A compensation function mitigates a substantial portion of the dispersion imparted to a communications signal by an optical communications system. A digital input signal is digitally processed using the compensation function to generate a predistorted signal. An amplitude and a phase of an optical signal are modulated using a pair of orthogonal signal components to generate a predistorted optical signal for transmission. In one implementation, the pair of orthogonal signal components are components of the predistorted signal. In another implementation, the predistorted signal is processed using a non-linear compensator to generate a further distorted signal and the pair of orthogonal signal components are components of the further distorted signal. In that implementation, the non-linear compensator is configured to substantially compensate for nonlinearities in one or both of an optical modulator of a transmitter of the system and an optical-to-electrical converter of a receiver of the system.

Abstract: A compensation function mitigates a substantial portion of the dispersion imparted to a communications signal by an optical communications system. A digital input signal is digitally processed using the compensation function to generate a predistorted signal. An amplitude and a phase of an optical signal are modulated using a pair of orthogonal signal components to generate a predistorted optical signal for transmission. In one implementation, the pair of orthogonal signal components are components of the predistorted signal. In another implementation, the predistorted signal is processed using a non-linear compensator to generate a further distorted signal and the pair of orthogonal signal components are components of the further distorted signal. In that implementation, the non-linear compensator is configured to substantially compensate for nonlinearities in one or both of an optical modulator of a transmitter of the system and an optical-to-electrical converter of a receiver of the system.

Abstract: A compensation function mitigates a substantial portion of the chromatic dispersion imparted to a communications signal by an optical communications system. A digital input signal is digitally processed using the compensation function to generate a predistorted signal. An amplitude and a phase of an optical signal are modulated using a pair of orthogonal signal components to generate a predistorted optical signal for transmission. In one implementation, the pair of orthogonal signal components are components of the predistorted signal. In another implementation, the predistorted signal is processed using a non-linear compensator to generate a further distorted signal and the pair of orthogonal signal components are components of the further distorted signal. In that implementation, the non-linear compensator is configured to substantially compensate for nonlinearities in one or both of an optical modulator of a transmitter of the system and an optical-to-electrical converter of a receiver of the system.

Abstract: A compensation function mitigates a substantial portion of the chromatic dispersion imparted to a communications signal by an optical communications system. A digital input signal is digitally processed using the compensation function to generate a predistorted signal. An amplitude and a phase of an optical signal are modulated using a pair of orthogonal signal components to generate a predistorted optical signal for transmission. In one implementation, the pair of orthogonal signal components are components of the predistorted signal. In another implementation, the predistorted signal is processed using a non-linear compensator to generate a further distorted signal and the pair of orthogonal signal components are components of the further distorted signal. In that implementation, the non-linear compensator is configured to substantially compensate for nonlinearities in one or both of an optical modulator of a transmitter of the system and an optical-to-electrical converter of a receiver of the system.

Abstract: Optical dispersion imposed on a communications signal conveyed through an optical communications system is compensated by modulating the communications signal in the electrical domain. A compensation function is determined that substantially mitigates the chromatic dispersion. The communications signal is then modulated in the electrical domain using the compensation function. In preferred embodiments, compensation is implemented in the transmitter, using a look-up-table and digital-to-analog converter to generate an electrical predistorted signal. The electrical predistorted signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical communications system.

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: An optical communications system for conveying traffic through an optical link between transmitting and receiving nodes. The system comprises, for each node, respective legacy and bypass paths coupled in parallel between the optical link and the node. The legacy path of each node includes an optical dispersion compensation block for compensating a respective portion of dispersion of the link. Thus the present invention provides a system architecture by which an optical communications system can be constructed using conventional modulation and optical dispersion compensation technologies. Once installed, system growth can be accommodated using next generation transmitters (with electronic compensation) without stranding the legacy equipment. Legacy channels can also be upgraded to electronic compensation, as desired.

Abstract: A method of a conveying data through an optical communications system. An optical signal is received through the optical communication system, the optical signal comprising data symbols and SYNC bursts, each SYNC burst having a predetermined symbol sequence. The received optical signal is oversampled to generate a multi-bit sample stream. The sample stream is partitioned into blocks of contiguous samples, wherein each block of samples partially overlaps at least one other block of samples and encompasses at least one SYNC burst and a plurality of data symbols. Each block of samples is independently processed to detect a value of each data symbol.

Abstract: A commercially viable All-Raman system, is implemented by removing the dispersion compensating Fiber (DCF) and two stage amplifier at each span, and including a transmission path dispersion compensator which performs dispersion compensation on a transmission path basis. For example, by pre-compensating for the accumulated dispersion in the electrical domain at the transmitter, the gain of the Raman pumps at each span amplifier need only compensate for the loss within the span, without needing to compensate for the loss of a DCF. In addition there is provided a low-cost method for implementing a bidirectional Service Channel by modulating/demodulating low-rate data on the Raman pump. For example, a Raman amplifier can include an information source for producing a service channel signal which includes information to be communicated; and a modulator for modulating the Raman pump signal with the service channel signal.

Abstract: Optical dispersion imposed on a communications signal conveyed through an optical communications system is compensated by modulating the communications signal in the electrical domain. A compensation function is determined that substantially mitigates the chromatic dispersion. The communications signal is then modulated in the electrical domain using the compensation function. Electrical domain compensation can be implemented in either the transmitter or the receiver end of the communications system. In preferred embodiments, compensation is implemented in the transmitter, using a look-up-table and digital-to-analog converter to generate an electrical predistorted signal. The electrical predistorted signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical communications system.

Abstract: Polarization Dependent Effects (PDEs), including Polarization Mode Dispersion (PMD) and Polarization Dependent Loss (PDL) imposed on optical signals conveyed through an optical link are compensated by processing an input signal in the electrical domain prior to transmission. A compensation function is derived that at least partially compensates the PDEs. The communications signal is then processed in the electrical domain using the compensation function to generate an electrical predistorted signal. The electrical predistorted signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical link. The PDEs of the optical link operate of the predistorted optical signal such at that substantially undistorted optical signal is received at a receiving end of the link.

Abstract: A digital performance monitoring method and system for an optical communications system utilizes a channel monitor and a digital signal processor (DSP). The channel monitor is designed to monitor a respective channel signal of the optical communications system, and includes a sample memory for storing sample data including a set of sequential N-bit (where N>1) samples generated by an Analog-to-Digital (A/D) converter at a predetermined sample rate. The digital signal processor (DSP) is designed to calculate at least one performance parameter of the optical communications system based on the stored sample data. The sample rate of the A/D converter is at least equal to a baud rate of the channel, and preferably satisfies the Nyquist criterion. Multiple A/D converters may be used parallel to sample respective orthogonal components of the channel signal. In this case, the stored sample data may be representative of the complex E-field of the channel signal.

Abstract: Conventional adaptive equalizers often use the “sign/sign” algorithm as a low complexity means to adjust their tap weight coefficients by driving the correlation between its single-bit “error” and “data” signals to zero. This algorithm fails in the presence of strong residual intersymbol interference (ISI), since this ISI renders the “error” signal sufficiently inaccurate to mask the correlation between “data” and “error”. Failure manifests itself two-fold as an inability to achieve tap weight acquisition at startup, and an inability to track dynamic channel conditions. The invention described herein employs an adaptive estimator to compute the residual masking ISI terms that in turn control an adaptive error slicer to synthesize a modified single-bit “error” signal that remains correlated with the “data” signal.

Abstract: A carrier lock detector for a QPSK or 4-QAM system implements a lock detection algorithm that maps detected signals onto one of first and second areas associated with nominal states defined by (I2?I3)·(Q2?Q3) and Q1?Q2·(I1 I2I3+ I1I2I3)+( I1?I2)·(Q1 Q2Q3+ Q1Q2Q3), or alternatively, by ( I1?I2· Q2?Q3)+( Q1?Q2· I2?I3), respectively. When detected signals map onto one of the first areas, a first signal is generated. When detected signals map onto one of the second areas, a second signal is generated. When a difference between the first and second signals exceeds a threshold, a carrier lock detection signal is generated to enable a decoder. The carrier lock detector is able to detect carrier lock at a raw BER of 1e-2 or greater at a very low signal-to-noise ratio.

Abstract: A frequency-agile optical transceiver includes a shared local oscillator (LO), a coherent optical receiver and an optical transmitter. The LO operates to generate a respective LO optical signal having a predetermined LO wavelength. The coherent optical receiver is operatively coupled to the LO, and uses the LO signal to selectively receive traffic of an arbitrary target channel of an inbound broadband optical signal. The optical transmitter is also operatively coupled to the LO, and uses the LO to generate an outbound optical channel signal having a respective outbound channel wavelength corresponding to the LO wavelength.

Abstract: A method of a conveying data through an optical communications system. An optical signal is received through the optical communication system, the optical signal comprising data symbols and SYNC bursts, each SYNC burst having a predetermined symbol sequence. The received optical signal is oversampled to generate a multi-bit sample stream. The sample stream is partitioned into blocks of contiguous samples, wherein each block of samples partially overlaps at least one other block of samples and encompasses at least one SYNC burst and a plurality of data symbols. Each block of samples is independently processed to detect a value of each data symbol.

Abstract: Optical dispersion imposed on a communications signal conveyed through an optical communications system is compensated by modulating the communications signal in the electrical domain. A compensation function is determined that substantially mitigates the chromatic dispersion. The communications signal is then modulated in the electrical domain using the compensation function. In preferred embodiments, compensation is implemented in the transmitter, using a look-up-table and digital-to-analog converter to generate an electrical predistorted signal. The electrical predistorted signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical communications system.

Abstract: A carrier lock detector for a QPSK or 4-QAM system implements, a lock detection algorithm that maps detected signals onto one of first and second areas associated with nominal states defined by (I2?I3)·(Q2?Q3) and {overscore (Q1?Q2)}·(I1{overscore (I2I3)}+{overscore (I1)}I2I3)+({overscore (I1?I2)})·(Q1{overscore (Q2Q3)}+{overscore (Q1)}Q2Q3), or alternatively, by ({overscore (I1?I2)}·{overscore (Q2?Q3)})+({overscore (Q1?Q2)}·{overscore (I2?I3)}), respectively. When detected signals map onto one of the first areas, a first signal is generated. When detected signals map onto one of the second areas, a second signal is generated. When a difference between the first and second signals exceeds a threshold, a carrier lock detection signal is generated to enable a decoder. The carrier lock detector is able to detect carrier lock at a raw BER of 1e-2 or greater at a very low signal-to-noise ratio.