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: In a method of estimating a bit rate (f1) of a digital signal conveyed through a SONET network between an originating node and a terminating node, the digital signal received by the originating node is processed to determine a result of a first function of the signal bit rate (f1) and a respective Tx local reference frequency (f2) of the originating node. A result of a second function of the Tx local reference frequency (f2) and a respective Rx local reference frequency (f3) of the terminating node is calculated. Finally, a result of a third function of the respective first and second function results is calculated, to derive an estimate of the signal bit rate (f4) relative to the Rx local reference frequency (f3).

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: A method and system is provided for compensating polarization mode dispersion (PMD) in an optical communications system includes a controller designed to control a broadband PMD compensator to differentially delay light at each one of a plurality of selected wavelengths. At least one of the selected wavelengths lies between an adjacent pair of channel wavelengths of the optical communications system. A performance parameter value indicative of PMD is measured at each channel wavelength of the optical communications system. An estimated performance parameter value is then calculated at each selected wavelength, and an error function calculated as a function of wavelength based on the estimated performance parameter values. The broadband PMD compensator is then controlled to minimize the value of the error function.

Abstract: A method and system for mitigating effects of dispersion in an optical link. A pair of digital sample streams are synthesized representing a target optical E-field having a spectrum selected such that the convolution of the spectrum with itself yields a signal having beat terms that contain phase information of the target optical E-field. A complex optical modulator is driven in accordance with the computed orthogonal sample values.

Abstract: A method and system enables measurement of polarization dependent loss (PDL) in an optical communications system including a plurality of cascaded optical components. An optical signal having a predetermined initial polarization state is launched into the optical communications system. A polarization state of the signal is detected at a selected detection point downstream of the launch point. The PDE is evaluated using the predetermined initial polarization state and the detected polarization state.

Abstract: A synchronizer/de-synchronizer maps continuous format signals of an arbitrary rate into frames of pre-selected single common rate, such as SONET frames, with no bite changed and very little jitter or wander added. In this way, the continuous format signal may be carried transparently as a tributary of a SONET network. Each frame comprises a definite number of fixed stuff bits, including transport overhead bits and reminder fixed stuff bits. A frame also comprises an adjustable number of adaptive stuff bits, resulting from the phase difference between the arbitrary rate and the common rate. A mapping function is performed in a tributary unit shelf of a SONET transport shelf, and the reverse mapping function is performed in a similar way at the far end of a SONET connection. The stuff bits are spread uniformly within the frame.

Abstract: A method of modulating an optical carrier. A target carrier modulation is computed based on an input data signal. An effective length of an optical modulator is then controlled based on the target carrier modulation.

Abstract: Provided is an optical apparatus and method wherein power transfer coefficients arising from SRS are measured at a designated co-location point and the power of dithers, which are impressed on the channels of a multiplexed optical signal propagating through the optical apparatus, is measured at each co-location point. Within the optical apparatus distances between co-location points are short and the power transfer coefficients are effectively constant. Consequently, the power of each channel of the multiplexed optical signal at the co-location points is obtained from the power of the dithers at a respective one of the co-location points and the power transfer coefficients measured at the designated co-location point. In some embodiments, information on the channel power at the co-location points is used to provide instructions for compensating for fluctuations in channel power and/or channel count at an input and/or channel count within the optical apparatus.

Abstract: A synchronizer/de-synchronizer maps continuous format signals of an arbitrary rate into frames of pre-selected single common rate, such as SONET frames, with no bits changed and very little jitter or wander added. In this way, the continuous format signal may be carried transparently as a tributary of a SONET network. Each frame comprises a definite number of fixed stuff bits, including transport overhead bits and reminder fixed stuff bits. A frame also comprises an adjustable number of adaptive stuff bits, resulting from the phase difference between the arbitrary rate and the common rate. A mapping function is performed in a tributary unit shelf of a SONET transport shelf, and the reverse mapping function is performed in a similar way at the far end of a SONET connection. The stuff bits are spread uniformly within the frame.

Abstract: A network node includes a system enabling high-speed protection switching of traffic between respectively associated working and protection channels of a communications network. The node comprises a multi-stage switch fabric, an interface, and a toggle. The multi-stage switch fabric has a first stage including a respective plurality of stage-1 switch elements. The interface is operatively coupled to a set of one or more stage-1 switch elements, and is adapted to aggregate the working and protection channels of the communications network on a selected one of the set of stage-1 switch elements. Finally, the toggle is adapted to control the selected stage-1 switch element to map traffic between a middle stage of the switch fabric and a selected one of the working and protection channels.

Abstract: The present invention discloses a high performance optical architecture for multiplexing and demultiplexing channels for use in high spectral efficiency optical systems. In general, the MUX and DeMUX architectures of the present invention will fall into two key sections or stages: a wavelength group section and a channel section. The group section makes use of characteristic associated with groups of multiplexed channels for separating said groups from an optical signal having a plurality of multiplexed groups. Advantageously, in preferred embodiments, the channel section is colorless (non-wavelength specific between groups) in order to reduce cost and complexity. With respect to the colorless channel section, components with free spectral ranges (FSRs) have been strategically added to provide repetitive optical filtering functions on group of channels (i.e., subsets of channels within each band of wavelengths) so that the colorless channel section can operate in any respective group identically.

Abstract: A serial data stream is mapped through a cross-connect via two or more parallel independent shelves. The serial data stream is split into at least two sub-streams. If the lead frame of a sub-stream contains a concatenation indicator, it is replaced by a valid payload pointer, and a spilt indicator is inserted into the frame. Each of the sub-streams is then mapped through the cross-connect via a respective parallel independent shelf. Finally, the sub-streams are recombined to form an output serial data stream equivalent to the original serial data stream. If the lead frame of a sub-stream contains a split indicator, a concatenation indicator is inserted into the corresponding frame of the output serial data stream to restore the concatenation of the original serial data stream. Otherwise, a payload pointer within the lead frame is replaced by a valid payload pointer in the corresponding frame of the output data stream.

Abstract: An OP-N connection is mapped through a communications network between first and second end-nodes via at least one intermediate node. The integrity and validity of the OP-N connection can be determined independently of SONET/SDH lines, sections or paths mapped through the network, and potentially utilizing bandwidth of the OP-N connection. Validation of the OP-N connection can be accomplished by inserting performance monitor (PM) information into a data signal at the first end-node. In some embodiments, the PM information is inserted into an unused portion of the transport overhead (TOH) of a SONET/SDH data signal. At each intermediate node between the first and second end-nodes, the PM information is extracted from the data signal, buffered while the data signal is pointer processed, and the reinserted before forwarding the data signal. Finally, a the second end-point, the PM information is extracted and examined.

Abstract: A method and system for reducing non-linear signal degradation effects of WDM optical signals exacerbated by highly correlated bit patterns of optical waveforms in neighboring optical channels. Embodiments include offsetting the transmission times of signals in neighboring channels, and applying different scrambling patterns to the respective data streams prior to transmission on neighboring optical channels.

Abstract: Optical equalization across N (an integer, N>1) channels of a multi-channel link of a communications network, is accomplished by averaging effects of optical performance variations within each of the M (an integer, M>1) parallel data signals. At a transmitting end node of the link, each one of the M data signals are distributed across the N channels of the link. Thus a substantially equal portion of each data signal is conveyed through the link in each one of the N channels. At a receiving end node of the link, respective bit-streams received over the N channels to are processed recover the M data signals. As a result, bit error rates of the bit-streams received through each channel are averaged across the M data signals, all of which therefore have a substantially equal aggregate bit error rate.

Abstract: A signal processor is adapted for aligning two or more hyper-concatenated data streams, each data stream being conveyed within a respective parallel channel and having substantially equivalent bit and frame rates. The signal processor comprises a respective channel processor for each channel for processing a respective data stream. Each channel processor includes a framer, a memory, an interface, and an output timer. The framer generates a local strobe signal indicative of a timing of incoming frames of the respective data stream. The memory buffers incoming bits of the respective data stream. The interface selectively sends the local strobe signal to, and receives a master strobe signal from, an adjacent channel processor. The output timer controls a timing of outgoing bits of the respective data stream based on a selected one of the local and master strobe signals.

Abstract: A framer is adapted for framing a high error rate data signal received through a link of a communications network, the data signal comprising M (an integer, M>1) interleaved sub-streams. The framer includes means for detecting a respective unique synchronizing word within each sub-stream. Each respective unique synchronizing word comprises: a non-unique position word having a first predetermined hamming distance; and a non-unique identifier word having a second predetermined hamming distance. The framer preferably includes M individual framers, and a master framer. Each individual framer operates to search the data signal to detect a respective one of the respective unique synchronizing words; and assert a respective individual frame found state for a first predetermined period of time when a respective one of the unique synchronizing words is found.

Abstract: Synchronization and desynchronization of a data signal transported in a synchronous frame across a synchronous communications network, such as SONET/SDH, reduces waiting-time jitter. A timing estimate (F) indicative of a relationship between a data rate (f1) of the data signal and a reference frequency (f2) of the synchronous communications network is calculated and communicated through the synchronous communications network, for example in the Synchronous Payload Envelope of a SONET frame. The data signal is recovered using a desynchronizer Phase-Locked Loop steered by the timing estimate (F). The timing estimate (F) can be any one or more of: a ratio between the data rate (f1) and the reference frequency (f2); a difference between the data rate (f1) and the reference frequency (f2); and a phase difference between a recovered data clock signal associated with the data rate (f1) and a reference clock signal associated with the reference frequency (f2).