Cisco Technology, Inc.

Christopher R Fludger

Thomas Duthel

Soeren Gehrke

Johann B Schiessl

Joerg Leykauf

Karsten Michaelsen

Andreas Bernhard Bisplinghoff

Gregory Alan Bryant

Mohammad Ali Sedaghat

A random noise generator for generating a plurality of random noise samples per clock cycle, the noise samples having a distribution. The random noise generator comprises at least a first comparator unit and a second comparator unit, the first comparator unit configured to generate a first plurality of samples representing a high-probability part of the distribution and the second comparator unit configured to generate a second plurality of samples representing a low-probability part of the distribution; and a random selection unit connected to at least the first comparator unit and the second comparator unit. The random selection unit is configured to receive the first plurality of samples generated by the first comparator unit and the second plurality of samples generated by the second comparator unit, to output a random selection of samples from the first plurality of samples and the second plurality of samples.

Random noise generation

A method for digital resampling in a digital communications receiver is described. The method comprises selecting whole samples of a received input signal in the time domain and implementing sub-sample digital interpolation in the frequency domain. This amounts to performing the time shift of the interpolation process in the frequency domain. The method may be performed in conjunction with the operation of a polarisation recovery filter. A digital communications receiver is also provided the receiver being arranged to perform frequency domain sub-sample interpolation on an input data signal.

Digital resampling method and apparatus

One or more operational parameters associated with pluggable optical transceivers are estimated to mitigate impairments to an optical signal caused by imperfections in the optical transceivers. A monitoring algorithm within a receiver signal processor may further use the estimated operational parameters associated with the pluggable optical transceivers to determine whether the transceivers are performing correctly. If the monitoring algorithm determines that either the transmitting or receiving optical transceiver is not functioning correctly, it may generate an alarm signal to notify a system administrator about the damaged device.

Optical transceiver compensation, monitoring and alarming

A receiver for an optical communications system which corrects distortion of a received signal. A clock recovery system utilizing a feedback and feedforward system are provided. The feedback loop comprises a phase detector and a clock source, while the feedforward loop comprises the phase detector and a delay element for delaying the output of distortion correction system. The feedback loop has a significantly lower bandwidth than the feedforward path. There are also provided methods of optimizing tap weights and of acquiring initial tap weights.

Clock recovery for optical transmission systems

A self-calibration procedure for an optical transmitter is provided. During the self-calibration procedure, a phase bias of an optical modulator of the optical transmitter is set so that an in-phase path and a quadrature path of the optical modulator are in phase. Stimulus signals are supplied to the in-phase and quadrature paths of the optical modulator, over a frequency range. Detection, with a photodetector, is made of an optical output of the optical modulator at a plurality of frequency steps over the frequency range. A photodetector converts an optical output of the optical modulator to an electrical signal. First and second measurement values are generated from the electrical signal output from the photodetector. A frequency spectrum and/or time delay is computed from the first and second measurement values for each frequency step value over the frequency range.

Transmitter self-calibration of time delay and frequency response for high baud-rate QAM transceivers

A system includes a laser configured to generate a tunable optical frequency. The system also includes an optical transmitter to map baseband data to symbols represented in a digital modulation constellation, add a frequency offset to the digital modulation constellation to cause the digital modulation constellation to rotate at a rate equal to the added frequency offset, modulate the optical frequency with the rotating digital modulation constellation, and transmit the resulting modulated optical frequency. The system also includes an optical receiver to receive the transmitted modulated optical frequency and, using the tunable optical frequency, detect the rotating digital modulation constellation conveyed by the received modulated optical frequency.

Control of LO signal frequency offset between optical transmitters and receivers

In an optical receiver, an optical local oscillator (LO) frequency is generated. A modulated optical frequency is received at the optical receiver. An LO-signal frequency offset between the received modulated optical frequency and the optical LO frequency is determined. A determination is made as to whether the LO-signal frequency offset is in one of multiple predefined non-overlapping target windows that cover respective non-zero LO-signal frequency offsets. If it is determined that the LO-signal frequency offset is not in one of the target windows, the optical LO frequency is tuned to drive the LO-signal frequency offset toward one of the target windows to ensure the LO-signal frequency offset is non-zero.

This invention relates to a phase control circuit for an optical receiver (). The phase control circuit () comprises a non-linear element () and a power detector (). The non-linear element () has a rectifying characteristic, inputs the received electrical signal () and provides a rectified signal at its output. The power detector () provides an error signal which is used to obtain a phase control signal () which is output by the phase control circuit. The invention further relates to a corresponding method for phase control of an optical receiver ().

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Nuremberg, Germany

Christopher R Fludger