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 suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: A method of testing a dual-polarization optical transmitter comprising a pair of polarization transmitters for respectively generating first and second polarization signals, and a polarization combiner for generating an optical signal composed of the first and second polarization signals with respective orthogonal polarization vectors. Each of the polarization transmitters is controlled to transmit respective polarization optical signals having predetermined characteristics. An output of the dual-polarization optical transmitter is tapped to obtain a first tap signal representative of the first polarization signal, and a second tap signal representative of the second polarization signal. A relative angle between respective polarization vectors of the tap signals is controlled, and the first and second tap signals combined to generate a combined light. A power level of the combined light is detected, and processed to obtain information about the performance of the dual polarization transmitter.

Abstract: A system for transmitting a plurality of data channels and an optical service channel through an optical fiber link of a Wavelength Division Multiplexed (WDM) optical communications system. The system comprises a first transmitter at a first end of the optical fiber link, for transmitting the data channels as a wavelength division multiplexed optical signal through the optical fiber link in a first direction. A second transmitter is connected at a second end of the optical fiber link, for transmitting the optical service channel through the optical fiber link in a second direction opposite to the first direction.

Abstract: A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: A method of synthesizing a modulated optical signal using a laser cascaded with an amplitude modulator. A phase drive signal VF(t) is derived for driving the laser to generate an optical carrier signal with a desired phase ?(t). An amplitude drive signal VS(t) is then derived for driving the amplitude modulator to impose a desired amplitude S(t) onto the optical carrier signal generated by the laser. The amplitude drive signal VS(t) is compensated for amplitude modulation of the optical carrier signal generated by the laser.

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 digital filter is provided for processing an electrical input signal to be conveyed through an optical communications system. The processing generates a predistorted electrical signal using a compensation function that substantially mitigates for intra-channel non-linearity imparted to the communications signal by the optical communications system. The digital filter has a memory having a limited size storing a reduced data set used for approximating an original, unreduced data set used to implement the compensation function. The reduced data set is used for the digital filter to apply the compensation function to mitigate the intra-channel non-linearity over longer transmission distances of the optical communications system than would be possible without the use of the reduced data set.

Abstract: A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: A method of processing a stream of digital samples of an optical signal received by a coherent optical receiver. The digital sample stream is processed to generate a dispersion compensated sample stream. The dispersion compensated sample stream is then processed to compensate polarization dependent impairments of the optical signal.

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: An optical spike is generated at an arbitrarily selected location within an arbitrary optical link. The optical spike is generated by deriving a spike signal having a plurality of components, and launching the spike signal into the a transmitter end of the optical link. An initial phase relationship between the components is selected such that the involved signal components will be phase aligned at the selected location. In order to achieve this operation, the initial phase relationship between the components may be selected to offset dispersion induced phase changes between the transmitter end of the link and the selected location. One or more optical spikes can be generated at respective arbitrarily selected locations within the link, and may be used for performance monitoring, system control, or other purposes.

Abstract: A control system for use in compensating for temperature-induced dispersion drift of an optical path, comprising an input adapted to obtain temperature data associated with the optical path; a control module adapted to determine control information on the basis of the temperature data; and an output adapted to provide a control signal to a dispersion compensator. The control signal is determined such that its receipt by the dispersion compensator causes the latter to induce a dispersive effect in a signal that travels the optical path, the dispersive effect being related to the control information. The ability to compensate for temperature-induced dispersion drift reduces the distortion margin in optical link budgets, allowing optical links to have longer reach, or to achieve the same reach using fewer line amplifiers. In a specific embodiment, dispersion compensation is accomplished via an open-loop control system such that feedback from the receiver site is not required.

Abstract: A method of processing a stream of digital samples of an optical signal received by a coherent optical receiver. The digital sample stream is processed to generate a dispersion compensated sample stream. The dispersion compensated sample stream is then processed to compensate polarization dependent impairments of the optical signal.

Abstract: Laser line-width compensation is performed by detecting noise in an optical signal output by a laser of an optical communications system and controlling a complex modulator to cancel the detected noise. Line-width compensation can be performed for both amplitude and phase noise in the optical signal. Noise measurements are used to compute a complex scalar. The complex scalar is used by a compensation processor to modify an input signal that is to be transmitted by the optical communications system. The modified input signal controls the complex modulator, which modulates the output signal to cancel the noise.

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 method for modulating the E-field of an optical carrier signal utilizes a Mach-Zehnder modulator having a pair of independently controllable branches. A pair of independent branch drive signals VL(t) and VR(t) are derived. Each branch of the MZ modulator is driven with a respective one of the independent branch drive signals. By this means, a low cost conventional MZ modulator (interferometer) can be used to perform complex modulation of the E-field of the optical carrier. In some embodiments, this functionality is used to facilitate precompensation of optical impairments of an optical communications system.

Abstract: An optical communications system is adapted for connection to an optical fiber link of an optical communications network. The system obtains a fiber identifier respecting the optical fiber link; a respective optimum setting of one or more parameters of the optical communications system; and adjusts a respective value of each parameter in accordance with the respective optimum setting. The fiber identifier can be obtained from a value of at least one fiber transmission property of the optical fiber link. The fiber transmission property value is used to search a look-up table of class definitions, each class definition including a respective class identifier and at least one corresponding characteristic transmission property value. A class identifier is selected as the fiber identifier from the class definition for which each characteristic transmission property value most closely matches a corresponding fiber transmission property value.

Abstract: An optical spike is generated at an arbitrarily selected location within an arbitrary optical link. The optical spike is generated by deriving a spike signal having a plurality of components, and launching the spike signal into the a transmitter end of the optical link. An initial phase relationship between the components is selected such that the involved signal components will be phase aligned at the selected location. In order to achieve this operation, the initial phase relationship between the components may be selected to offset dispersion induced phase changes between the transmitter end of the link and the selected location. One or more optical spikes can be generated at respective arbitrarily selected locations within the link, and may be used for performance monitoring, system control, or other purposes.