Alcatel Lucent

Alcatel-lucent USA Inc.

Timo Pfau

Noriaki Kaneda

Brian S Krongold

Xiang Liu

Young-Kai Chen

Chandrasekhar Sethumadhavan

Giancarlo Gavioli

Jeffrey Lee

Qi Yang

An optical receiver includes an equalizer to generate a plurality of equalization coefficients corresponding to a plurality of frequencies of an optical signal received by the optical receiver. The equalizer zeroes out a first subset of the equalization coefficients corresponding to a first subset of the plurality of frequency components and applies a second subset of non-zero equalization coefficients to the first signal. The optical receiver may also include a chromatic dispersion compensator to generate inverse chromatic dispersion coefficients corresponding to the plurality of frequency components, and to zero out a first subset of the inverse chromatic dispersion coefficients corresponding to the first subset of the plurality of frequency components and further to apply a second subset of non-zero inverse chromatic dispersion coefficients to a second optical signal.

Low power equalizer for an optical receiver

Embodiments of the disclosure include a method and apparatus for detecting and removing cycle slip. A phase-modulated signal having a plurality of phase-modulated symbols is received at an optical receiver, and, for each phase-modulated symbol, a phase-error estimate of a phase error of the phase-modulated symbol is generated. The presence of a cycle slip is then detected based on the phase-error estimates, and, a phase of each of one or more of the received phase-modulated symbols is adjusted to remove the detected cycle slip without adjusting a local oscillator.

Detection and removal of cycle slip from received signals

An optical transport system is configured to use a modulation scheme in which a phase rotation applied to a sequence of PSK or QAM constellation symbols encoding a codeword of an FEC code produces a modified sequence of PSK or QAM constellation symbols encoding a bit-word that is not a valid codeword of that FEC code. Based on this property of the modulation scheme, an optical receiver may be configured to relatively accurately recover the absolute phase of the optical carrier wave of the received modulated optical signal by applying maximum likelihood sequence estimation processing to each portion of the signal carrying a valid codeword of the FEC code. For example, for a modulation scheme employing a 2-PSK constellation, the optical receiver may be able to recover the absolute phase of the optical carrier wave with an accuracy that is better than 360/2degrees.

Use of parity-check coding for carrier-phase estimation in an optical transport system

One aspect provides an optical communication system. The system includes an optical-to-digital converter, a frequency estimator and a symbol synchronizer. The optical-to-digital converter is configured to receive an optical OFDM bit stream including an OFDM symbol bearing payload data and a symbol header preceding the OFDM payload data. The frequency estimator is configured to determine a carrier frequency offset of the payload data from the symbol header. The symbol synchronizer is configured to determine a starting location of the payload data within the bit stream by cross-correlating a synchronization pattern within the symbol header with a model synchronization pattern stored by the symbol synchronizer.

Frame/symbol synchronization in coherent optical OFDM

An apparatus, e.g. an optical receiver, includes an optical front end and an equalizer. The front end is configured for receiving an optical signal bearing first and second symbols on respective first and second polarization channels. The equalizer is configured to 1) select a first cost function if the first symbol has greater energy than the second symbol, 2) select a second different cost function if the second symbol has a greater energy than the first symbol, and 3) based on the selected cost function, update coefficients of an adaptive filter configured to demultiplex and equalize the first and second polarization channels.

Blind equalization for polarization-switched QPSK optical communications

An optical transport system that transmits data using relatively short FEC-encoded data frames. The corresponding modulated optical signals are decoded at an optical receiver using frame-based maximum likelihood sequence estimation that relies on data redundancy present in each FEC-encoded data frame for the determination of its source bits. In some embodiments, the modulated optical signals carrying the FEC-encoded data frames are generated using a polarization-division-multiplexed constellation. The FEC-coding rate and frame length can be adjusted without changing the constellation, which advantageously enables the optical transport system to dynamically adapt its transmission format to the changing link conditions in a manner that results in better overall receiver sensitivity than that achieved with comparable bit-rate-adaptation methods that rely on a constellation change rather than on a change of the FEC-coding rate.

Forward error correction for an optical transport system

A system, e.g. for optical communication, includes an I-Q modulator and a transmission signal processor. The I-Q modulator is configured to modulate a first light source in response to first I and Q modulation signals. The transmission signal processor is configured to receive a data stream including data corresponding to a first data subchannel. The processor maps the data subchannel to an optical transmission subchannel and outputs the first I and Q modulation signals. The I and Q modulation signals modulate the light source to produce an optical transmission signal that includes wavelength components corresponding to the optical transmission subchannel.

Ultra dense WDM with agile and flexible DSP add-drop

Various embodiments of a 16-QAM (quadrature-amplitude-modulation) constellation having one or more subsets of its sixteen constellation points arranged within respective one or more relatively narrow circular bands. Each of the subsets includes constellation points of at least two different amplitudes and may have between about six and about ten constellation points. Each of the circular bands may have a width that is between about 3% and about 20% of the maximum amplitude in the constellation.

Noise-resilient constellations for an optical transport system

In one embodiment, a coherent optical receiver has an optical detector coupled to a digital processor. The optical detector mixes a received modulated optical signal with a local-oscillator signal to produce a digital measure of the modulated optical signal. The digital processor processes the digital measure using a primary carrier- and data-recovery (CDR) stage and one or more secondary CDR stages serially connected to one another. The processing performed in each secondary CDR stage is decision-directed and uses the symbol estimate generated by the preceding CDR stage to obtain a respective estimate of the carrier-phase offset and a respective symbol estimate. Since each subsequent CDR stage typically improves the accuracies of its estimates compared to those of the preceding CDR stage(s), the receiver has a lower bit-error rate than a receiver employing a single CDR stage.

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Westfield, NJ, United States of America

Timo Pfau