Alcatel Lucent

Nokia Solutions and Networks Oy

Nokia of America Corporation

Chandrasekhar Sethumadhavan

Xiang Liu

Peter Johannes Winzer

Robert William Tkach

Alan H Gnauck

Andrew Roman Chraplyvy

Gregory Raybon

Timo Pfau

Joon Ho Cho

Giancarlo Gavioli

Xi Chen

Andrew Adamiecki

Chraplyvy R Andrew

A communication system in which probabilistic signal shaping and FEC coding are jointly applied in a manner that enables the use of substantially any constellation template, e.g., a template in which the constellation symbols include a constellation symbol of zero amplitude and/or are arranged in an asymmetric manner. In an example embodiment, the transmitter's electronic encoder can be configured to apply two different respective shaping codes to the information bits and to the corresponding parity bits. The resulting shaped streams can then be appropriately multiplexed and transmitted over the optical communication channel to realize a significant shaping gain. Advantageously, the constellation template(s), two distribution matchers, and FEC code can be flexibly selected and/or adapted to achieve nearly optimal system operation under substantially arbitrary (e.g., arbitrarily bad) channel conditions.

Methods and apparatus for joint use of probabilistic signal shaping and forward error correction

An optical WDM system configured to use direct detection of communication signals that is compatible with electronic CD compensation on a per-channel basis. In an example embodiment, to enable full (e.g., amplitude and phase) electric-field reconstruction at the receiver, the optical WDM system uses a carrier-frequency plan according to which the carrier-frequency comb used at one end of the WDM link and the carrier-frequency comb used at the other end of the WDM link are offset with respect to one another by one half of the bandwidth of an individual WDM component transmitted therethrough. This frequency offset places each local carrier frequency at a roll-off edge of the corresponding incoming data-modulated signal. As a result, the corresponding combined optical signal beneficially lends itself to direct detection that can be followed by full electric-field reconstruction using a known self-coherent Kramers-Kronig method and then by conventional electronic CD compensation.

Optical transport system employing direct-detection self-coherent receivers and compatible transmitters

We disclose an optical transponder, in which one or more all-electronic feedback paths are used to obtain a relatively accurate estimate of the device-specific signal distortions in the transmitter portion thereof. The obtained estimate is used to enable the digital signal processor of the optical transponder to carry out electronic pre-distortion (EPD) that can significantly reduce or cancel these signal distortions without the use of detailed factory-calibration measurements or optics dedicated to feedback purposes. The use of all-electronic feedback paths may enable a beneficial reduction in the cost of the EPD functionality, e.g., by eliminating a significant extra cost associated with the implementation of optically generated feedback.

Feedback for electronic pre-distortion in an optical transmitter

A space division multiplexed (SDM) transmission system that includes at least two segments of transmission media in which a spatial assignment of the two segments is different is provided. For example, the SDM transmission may include a first segment of transmission media having a first spatial assignment and a second segment of transmission media having a second spatial assignment, wherein the first spatial assignment differs from the second spatial assignment. An example method obtains an optical signal on a first segment of transmission media having a first spatial assignment and forwards the optical signal on a second segment of transmission media with a different spatial assignment. The transmission media may be a multi-core fiber (MCF), a multi-mode fiber (MMF), a few-mode fiber (FMF), or a ribbon cable comprising nominally uncoupled single-mode fiber (SMF).

Method and apparatus for space-division multiplexing systems

An example apparatus comprises an optical transmitter which includes a first processor and at least two optical modulators. The first processor is configured to generate a first electronic representation for each of at least two optical signals for carrying payload data modulated according to a one-dimensional (1-D) modulation format, and to induce on respective ones of the first electronic representations an amount of dispersion that depends on a power-weighted accumulated dispersion (AD) of a transmission link through which the at least two optical signals are to be transmitted thereby generating complex-valued electronic representations of pre-dispersion-compensated optical signals. Each of the at least two optical modulators modulate a respective analog version corresponding to a respective one of the complex-valued electronic representations onto a polarization of an optical carrier.

Communication through multiplexed one-dimensional optical signals

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

In one embodiment, a coherent optical receiver has a digital signal processor that processes one or more digital I/Q-signal pairs to recover data carried by a modulated optical signal in a manner that mitigates, based on calibration data retrieved from a memory or on appropriate performance measures and feedback mechanisms, the detrimental effects of frequency-dependent imbalances between the I and Q sub-channels of at least one of the I/Q channels of the receiver. In various embodiments, the calibration data can be generated and written into the memory at the fabrication facility or in situ while the receiver is being operated in a calibration mode. Alternatively or in addition, the calibration data can be generated and dynamically adjusted online during normal operation of the receiver.

Frequency-dependent I/Q-signal imbalance correction coherent optical transceivers

Methods and apparatus for managing the effects of dispersion in an optical transport system in which some of the system's nodes are connected to one another via inhomogeneous fiber-optic links. In one embodiment, an optical transmitter is configured to apply electronic and/or optical dispersion pre-compensation in the amount selected to cause the peak-to-average-power ratio of the optical signal in the lower-dispersion portion of the link to be relatively low (e.g., close to a minimum value). Advantageously, such dispersion pre-compensation tends to significantly reduce, e.g., in terms of the bit-error rate, the directional anisotropy exhibited by optical transmissions through the inhomogeneous fiber-optic links.

Dispersion management for inhomogeneous fiber-optic links

Methods and apparatus for power-efficiently and reliably transmitting high-level quadrature amplitude modulation (QAM) optical signals using binary drive signals. Even though binary signals are used to drive a QAM modulator directly, without digital-to-analog conversion, the methods and apparatus disclosed allow the transmission of pilot symbol sequences having near optimal properties, such as a constant power profile in the time domain; a mean power that is approximately the same as the mean power of the data symbols; and roughly uniform amplitude in the frequency domain for non-zero frequency components of the pilot symbol sequence. The binary drive signals can be processed so that the modulated optical signals are selectively constrained to a subset of points of the QAM constellation to form a QAM constellation with reduced size and a mean power that is approximately the same as the mean power of the original QAM constellation.

Method and apparatus for transmitting high-level QAM optical signals with binary drive signals

An optical transmitter configured to perform digital signal equalization directed at mitigating the detrimental effects of a frequency roll-off in the transmitter's optical I-Q modulator. In various embodiments, a frequency-dependent spectral-correction function used for the digital signal equalization can be constructed to cause the spectrum of the modulated optical signal generated by the transmitter to have a desired degree of flatness in the vicinity of an optical carrier frequency and/or to at least partially mirror the frequency roll-off in the optical I-Q modulator.

Frequency equalization for an optical transmitter

Return To Zero (RZ) shaping is performed for a first I/Q modulator whose output corresponds to a first polarization component using a first two digital-to-analog convertors (DACs), each of which is sampled at approximately twice a modulation symbol rate or more and has an output with a first interleaving order that interleaves one of a first pair of intended drive signal patterns and zeros. RZ shaping is also performed for a second I/Q modulator whose output corresponds to a second polarization component using a second two DACs, each sampled at approximately twice the modulation symbol rate or more and having a second interleaving order that interleaves zeros and one of a second pair of intended drive signal patterns, the second interleaving order opposite the first interleaving order. The first polarization and the second polarization may be combined, thereby forming an Interleaved Return To Zero (IRZ) Polarization Division Multiplexed (PDM) signal.

Apparatus and method for generating interleaved return-to-zero (IRZ) polarization-division multiplexed (PDM) signals

In one embodiment, an optical transmission system transmits data using a format according to which a data frame has two or more pilot-symbol blocks, each having a guard interval, and two or more payload-symbol blocks that are concatenated without a guard interval between them. The use of guard intervals in the pilot-symbol blocks helps the synchronization and channel-estimation procedures performed at a receiver of the optical transmission system to be robust in the presence of certain transmission impairments. The absence of guard intervals in the payload-symbol blocks helps to minimize the transmission overhead and thus achieve relatively high payload-data throughput. Pilot-symbol blocks have a structure that enables the receiver to determine channel-response characteristics for each data frame and then apply appropriate channel-response-compensation procedures to signals corresponding to the payload-symbol blocks of the frame to recover, with a relatively low bit-error rate, the data encoded in those signals.

Pilot-assisted data transmission in a coherent optical-communication system

Systems, apparatus and method for modulating digital data onto an optical carrier to produce a modulated optical carrier in which symbol-modulated optical signals of orthogonal polarizations are temporally interleaved and adapted to be processed by electronic time-division demultiplexing to recover the digital data modulated onto the orthogonal polarizations of the optical signals.

System, apparatus and method for communicating data via polarization multiplexing

An optical phase conjugator that can be deployed within a long-haul fiber-optic link of an optical WDM system to improve the system's tolerance to intra- and inter-channel nonlinear effects. In one embodiment, the optical phase conjugator has a digital signal processor configured to perform, in the digital electrical domain, a phase-conjugation transformation for various components of a WDM signal so that certain signal distortions imposed on that signal in the front portion of the fiber-optic link are reduced in the back portion of the link. Advantageously, the optical phase conjugator is flexibly configurable to employ an input-to-output carrier-frequency-mapping configuration that is most beneficial under particular operating conditions. mapping configuration that is most beneficial under particular operating conditions.

Digital phase conjugation for fiber-optic links

A coherent optical receiver for a data-frame format in which a data frame has two or more pilot-symbol blocks, each having a cyclic prefix or suffix, and one or more payload-symbol blocks, each of which is concatenated with at least one adjacent block without a guard interval between them. The receiver uses optical signals corresponding to the pilot-symbol blocks to perform data-frame synchronization, frequency-offset correction, and channel-estimation procedures, which are robust even in the presence of certain transmission impairments. The receiver applies block-overlap processing with a sliding window to recover the payload data in a manner that substantially cancels the adverse effects of inter-block interference caused by the absence of guard intervals in the payload portion of the data frame. In one embodiment, the receiver performs channel-estimation and block-overlap processing for polarization-division-multiplexed signals in a manner that enables a combined, intertwined application of channel-response-compensation and polarization-demultiplexing procedures.

Growing community of inventors

Matawan, NJ, United States of America

Chandrasekhar Sethumadhavan