Abstract: Methods and apparatus for coherent transmitter calibration are provided that employ direct detection (DD) using one single photodetector (PD). The provided method and apparatus do not require hardware for coherent reception, or additional ADCs for quality control. An additional optical tone is added to a QAM optical signal that is outside the band of the QAM optical signal. The result of this is that after direct detection, there is a correlation between the real and imaginary parts, and the imaginary part can be recovered with a Hilbert transform. The estimated QAM optical signal obtained by direct detection is used to perform a transmitter factory calibration method to calibrate for one or more transmitter impairments and/or to perform in-line self-calibration.

Abstract: Apparatus and methods are provided for noise-whitening post-compensation in a receiver. A first apparatus includes a first whitening filter configured to filter a received signal comprising symbols to generate a first filtered signal. The first apparatus further includes a first decision feedback equalizer having an input coupled to an output of the first whitening filter to receive the first filtered signal. The first decision feedback equalizer is configured to apply decision feedback equalization to the first filtered signal to generate estimates for the symbols of the received signal. A second apparatus includes a decision device configured to generate a symbols decision based on a received signal comprising symbols, a noise predictor configured to predict noise in the received signal, and a subtractor configured to subtract the predicted noise from the received signal to generate a symbols estimate.

Abstract: A method includes distributing payload data among a master sub-band and a plurality of slave sub-bands. The master sub-band and the plurality of slave sub-bands collectively extend over an allocated frequency spectrum; the master sub-band and the plurality of slave sub-bands are associated with different carrier frequencies; and the master sub-band has a center frequency that corresponds to a center frequency of the allocated frequency spectrum. The method includes generating modulated data for the master sub-band and the plurality of slave sub-bands based on the distributed payload data; and transmitting an optical signal to an optical medium representing the modulated data.

Abstract: Aspects of the present disclosure are directed in part to a receiver DSP unit including an equalization module. The equalization module includes a trellis-based equalization module that may utilize multiple trellis-based processors (TBP), which can each be individually adaptively configured for performing a trellis-based equalization. The design of the TBPs allows them to be configured for compensating a residual Inter-Symbol Interference (ISI) as well as compensating a residual Phase Noise (PN). ISI is an example of an additive impairment and PN is an example of a multiplicative impairment that communication systems, particularly high speed transmission systems such as coherent optical systems, can suffer from.

Abstract: The disclosed systems, apparatuses and methods are directed to controlling optical channel signal and an optical network equipment in optical networks. The methods comprise adjusting an optical channel spectrum based on bit error rates (BER) measured for a dithered optical channel signal. The optical channel spectrum is dithered such that a signal reference frequency is alternated between a first second signal reference frequency and a second signal reference frequency. BER is measured and analysed separately for the dithered signal reference frequency being detuned to the first and to the second signal reference frequencies. Based on a BER difference between BER at the first signal reference frequency and BER at the second signal reference frequency, the optical channel spectrum is shifted with regards to frequency in order to improve optical network performance.

Abstract: Systems and methods are provided for adaptive equalization, for example for use with coherent optical reception. The equalizer has a loop for updating taps of an adaptive linear filter forming part of the equalizer. In the loop, an error calculator calculates an error, a gradient calculator calculates a gradient of the error or filtered error. One or more gradient filters are used to filter the gradient, and the filtered gradient is used to update the taps of the adaptive linear filter. A reduction in self oscillation in the equalizer is achieved by separating the frequencies with channel features that change with time and scaling them up to speed up convergence of the equalizer.

Abstract: Apparatus and methods are provided for noise-whitening post-compensation in a receiver. A first apparatus includes a first whitening filter configured to filter a received signal comprising symbols to generate a first filtered signal. The first apparatus further includes a first decision feedback equalizer having an input coupled to an output of the first whitening filter to receive the first filtered signal. The first decision feedback equalizer is configured to apply decision feedback equalization to the first filtered signal to generate estimates for the symbols of the received signal. A second apparatus includes a decision device configured to generate a symbols decision based on a received signal comprising symbols, a noise predictor configured to predict noise in the received signal, and a subtractor configured to subtract the predicted noise from the received signal to generate a symbols estimate.

Abstract: An embodiment method includes multiplexing light emitted by the plurality of optical transmitters to provide a multiplexed optical signal; propagating the multiplexed optical signal through an optical interleaver from a first port thereof to a combined port thereof and back to a second port thereof; and detecting an optical signal at the second port of the optical interleaver.

Abstract: An optical circuit switching matrix includes a plurality of optical ports, each optical port being optically coupled to a respective one of a plurality of user nodes and an optical coupler having at least one input port optically coupled to the plurality of optical ports, and an output port. The optical circuit switching matrix also includes a wavelength demultiplexer having an input optically coupled to the output port of the optical coupler, and a plurality of output ports, each output port being optically coupled to a respective one of the plurality of optical ports.

Abstract: A symbol detection and forward error correction (FEC) decoding system and method are disclosed that aim to increase decoding performance and maintain an acceptable level of complexity. In one embodiment, the method includes performing detection and decoding over a plurality of iterations. During the first iteration: a first equalizer structure processes a received signal, and a FEC decoder performs decoding on an input obtained from the output of the first equalizer structure. During the other iterations: an iterative equalizer structure processes both (i) the received signal and (ii) an input obtained from an output of the FEC decoder from a previous iteration of the detection and decoding, in order to generate an output of the iterative equalizer structure, and the FEC decoder performs FEC decoding on an input obtained from the output of the iterative equalizer structure.

Abstract: Systems and methods are provided for adaptive equalization, for example for use with coherent optical reception. The equalizer has a loop for updating taps of an adaptive linear filter forming part of the equalizer. In the loop, an error calculator calculates an error, a gradient calculator calculates a gradient of the error or filtered error. One or more gradient filters are used to filter the gradient, and the filtered gradient is used to update the taps of the adaptive linear filter. A reduction in self oscillation in the equalizer is achieved by separating the frequencies with channel features that change with time and scaling them up to speed up convergence of the equalizer.

Abstract: Aspects of the present disclosure are directed in part to a receiver DSP unit including an equalization module. The equalization module includes a trellis-based equalization module that may utilize multiple trellis-based processors (TBP), which can each be individually adaptively configured for performing a trellis-based equalization. The design of the TBPs allows them to be configured for compensating a residual Inter-Symbol Interference (ISI) as well as compensating a residual Phase Noise (PN). ISI is an example of an additive impairment and PN is an example of a multiplicative impairment that communication systems, particularly high speed transmission systems such as coherent optical systems, can suffer from.

Abstract: The disclosure is directed to a method and system for generating a pilot tone for an optical signal with an optical telecommunications system. The pilot tone is generated in the digital domain by modulating the data to be transmitted to a destination node within the optical telecommunications network. The modulation of the data introduces occurrence modulation to the optical signal.

Abstract: The disclosure is directed to a method and system for generating a pilot tone for an optical signal with an optical telecommunications system. The pilot tone is generated in the digital domain by modulating the data to be transmitted to a destination node within the optical telecommunications network. The modulation of the data introduces occurrence modulation to the optical signal.

Abstract: An embodiment method includes multiplexing light emitted by the plurality of optical transmitters to provide a multiplexed optical signal; propagating the multiplexed optical signal through an optical interleaver from a first port thereof to a combined port thereof and back to a second port thereof; and detecting an optical signal at the second port of the optical interleaver.

Abstract: An optical transceiver is provided with an optical front end for receiving signal light comprising an optical sub-channel, and for providing an electrical signal based on the signal light; a light source optically coupled to the optical front end for providing local oscillator light thereto for mixing with the signal light; an electro-optical modulator coupled to the light source for receiving output light therefrom and for modulating the output light with digital information to obtain modulated light; and a signal processor operably coupled to the optical front end. The signal processor is configured for processing the electrical signal to obtain a frequency offset of the sub-channel; and adjusting an optical frequency of the modulated light based on the frequency offset. When applied to a multiple-access environment, this may allow access nodes to generate optical sub-channels in the uplink direction using the downlink optical signal as an optical frequency reference.

Abstract: The disclosure is directed to a method and system for generating a pilot tone for an optical signal with an optical telecommunications system. The pilot tone is generated in the digital domain by modulating the data to be transmitted to a destination node within the optical telecommunications network. The modulation of the data introduces occurrence modulation to the optical signal.

Abstract: An optical channel between a coherent optical transmitter and a coherent optical receiver may include one or more components that act as a bandpass filter with a passband that is narrower than the signal bandwidth. Such a narrow filter may significantly attenuate the signal content close to the band edge of the data signal. As a result, timing error detection may work less effectively, and therefore clock recovery may be less effective or fail. Methods and systems are disclosed in which a single optical carrier is used to transmit a data signal that has multiple bands, and timing error detection is performed at the receiver using one or more inner bands of the multiple bands. The timing error detection may therefore be made more robust to the effects of the narrow filtering.

Abstract: An optical transceiver is provided with an optical front end for receiving signal light comprising an optical sub-channel, and for providing an electrical signal based on the signal light; a light source optically coupled to the optical front end for providing local oscillator light thereto for mixing with the signal light; an electro-optical modulator coupled to the light source for receiving output light therefrom and for modulating the output light with digital information to obtain modulated light; and a signal processor operably coupled to the optical front end. The signal processor is configured for processing the electrical signal to obtain a frequency offset of the sub-channel; and adjusting an optical frequency of the modulated light based on the frequency offset. When applied to a multiple-access environment, this may allow access nodes to generate optical sub-channels in the uplink direction using the downlink optical signal as an optical frequency reference.

Abstract: An optical channel between a coherent optical transmitter and a coherent optical receiver may include one or more components that act as a bandpass filter with a passband that is narrower than the signal bandwidth. Such a narrow filter may significantly attenuate the signal content close to the band edge of the data signal. As a result, timing error detection may work less effectively, and therefore clock recovery may be less effective or fail. Methods and systems are disclosed in which a single optical carrier is used to transmit a data signal that has multiple bands, and timing error detection is performed at the receiver using one or more inner bands of the multiple bands. The timing error detection may therefore be made more robust to the effects of the narrow filtering.