Abstract: An optical transmission system includes an optical transmitter that includes first and second light sources, first and second phase modulators respectively modulating light from the first and the second light sources, and a polarized beam combiner combining the light output from the first and the second phase modulators to output an optical signal; and an optical receiver that includes a local oscillator, a polarization beam splitter splitting, according to polarization, the optical signal transmitted from the optical transmitter, and first and second digital coherent receivers corresponding to the first and the second phase modulators, and including a frontend that mixes light from the local oscillator and the polarization-split optical signal to output an electrical signal of real and imaginary parts, an analog-digital converting unit converting the electrical signal to a digital signal, and a digital signal processing unit estimating phase of the digital signal and extracting a signal.

Abstract: Polarization scattering compensation device and method are disclosed. In the device, a time sequence alignment unit aligns time sequences of signals in the first and second polarization state transmitted simultaneously; a polarization scattering estimation unit estimates a scattering coefficient of a scattering by the signal in the first polarization state on the signal in the second polarization state, and a scattering coefficient of a scattering by the signal in the second polarization state on the signal in the first polarization state; and a polarization scattering removal unit removes the scattering by the signal in the first polarization state on the signal in the second polarization state, and the scattering by the signal in the second polarization state on the signal in the first polarization state, in accordance with the scattering coefficients.

Abstract: 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.

Abstract: A method reduces time-varying polarization crosstalk due to XPolM by transmitting multi-dimensional orthogonal constellations. Three variants of crosstalk-free constellations are provided: Grassmann constellations, unitary constellations, and rotation codes. The method uses the Grassmann constellations and the unitary constellations to deal with fiber nonlinearity by applying as a polarization-time coding. The rotation codes exploit a fiber channel characteristic to improve performance and to reduce computational complexity. The underlying orthogonality behind those constellations enables the receiver to decode it as if there is no polarization crosstalk. Moreover, the required computational complexity at the receiver is significantly reduced because neither crosstalk cancellers nor channel estimators are needed.

Abstract: An optical apparatus includes a first beam combining device arranged to receive a first optical beam having a first wavelength at a first location and a second optical beam output having a second wavelength at a second location. The second optical beam has a polarization that is substantially orthogonal to a polarization of the first optical beam. The first beam combining device configured to output a first combined beam that comprises a combination of the first optical beam and the second optical beam. An optical element is arranged to receive the first combined beam and a second combined beam and to transmit an output beam that includes a combination of the first combined beam and the second combined beam.

Abstract: The present invention provides a system, apparatus and method to provide for amplification at various points along one or more optical paths of a photonic integrated circuit. According to various embodiments of the invention, the photonic integrated circuit includes a plurality of optical devices having associated characteristics which may have lead to optical signal degradation. One or more optical amplifiers provided along one or more optical paths of the photonic integrated circuit compensate for such signal degradation, resulting in a highly configurable photonic integrated circuit. The various optical devices of the photonic integrated circuit may be provided on a single substrate.

Abstract: The differential group delay is measured in an optical fiber connection for an optical signal undergoing a phase modulation BPSK or DPSK by a digital signal at a given rate. A polarization controller at an emerging end of the connection scans polarization states of the modulated optical signal. An emulator iteratively introduces an additional delay in the modulated optical signal emerging from the connection and combines the delayed modulated optical signal and the non delayed modulated optical signal which are both polarized along two orthogonal axes into a resulting optical signal. A polarization controller and a fixed polarizer select a polarization state in the resulting optical signal along one of bisecting lines of the orthogonal axes into a linearly polarized signal. An eye diagram or a spectrum of the polarized signal is acquired by a digital oscilloscope or an optical spectrum analyzer to determine the differential group delay.

Abstract: Signal light, pumping light and control light having different wavelengths are input to a nonlinear optical medium. The power of the pumping light is controlled to generate a desired gain in the nonlinear optical medium. The power of the control light is controlled to saturate the gain of the nonlinear optical medium.

Abstract: Polarization multiplexing with different differential phase shift keying (DPSK) schemes generally uses DPSK modulated signals modulated using different DPSK modulation schemes and combined with orthogonal polarizations relative to each other. The different DPSK modulation schemes may use different DPSK phase shifts to represent data, such as a regular DPSK modulation scheme and a ?/2 DPSK modulation scheme. By using different DPSK modulation schemes to represent data on the orthogonally polarized signals, the DPSK demodulators may effectively separate the orthogonally polarized signals using the property of the DPSK receivers. To optimize performance, the DPSK modulated signals may also be bit-interleaved when combined with orthogonal polarization.

Abstract: A demodulator includes: a splitter that branches a differential phase shift keying optical signal into a first branched optical signal passing through a first optical path and a second branched optical signal passing through a second optical path; a multiplexer that multiplexes the first branched optical signal having passed through the first optical path and the second branched optical signal having passed through the second optical path and makes interference between the first branched optical signal and the second branched optical signal; and a double refraction medium that reduces difference between phase differences between each polarized wave between the first branched optical signal and the second branched optical signal multiplexed by the multiplexer.

Abstract: An apparatus receives data encoded in a format where information bits for transmission are mapped into symbols each carrying a plurality of bits, some of which are encoded through a pulse position modulation (PPM) format and the rest of which are encoded through an additional modulation format on at least one PPM pulse. The receiver detects the signal through a dual-polarization coherent receiver front-end, and recovers polarization components of the signal by decoding a first non-zero portion of a plurality of bits carried by a symbol based on slot position of at least one PPM pulse in the polarization components and a second non-zero portion of the plurality of bits carried by the symbol based on the additional modulation carried by at least one PPM pulse in the polarization components. Pilot-assisted single-carrier frequency-division equalization (PA-SC-FDE) may be used for reliable signal reception in the presence of severe PPM errors.

Abstract: Embodiments of the present invention provide systems, devices and methods for managing skew within a polarized multi-channel optical transport system. In a DP-QPSK system, skew between polarized channels is compensated within the transport system by adding latency to at least one of the polarized channels. The amount of added latency may depend on various factors including the skew tolerance of the transport system and the amount of skew across the channels without compensation. This latency may be added optically or electrically, and at various locations on a channel signal path within a transport node, such as a terminal transmitter or receiver. Additionally, various embodiments of the invention provide for novel methods of inserting frame alignment bit sequences within the transport frame overhead so that alignment and skew compensation may be more efficiently and accurately performed at the transport receiver.

Abstract: A polarization multiplexing optical receiver includes a polarization controller configured to control a polarization state of a polarization multiplexed optical signal; a polarization splitter configured to split the polarization multiplexed optical signal for which the polarization state is controlled by the polarization controller into a first polarization signal and a second polarization signal; a first detector configured to detect an optical power of the first polarization signal and output a first optical power signal representing the optical power of the first polarization signal; a second detector configured to detect an optical power of the second polarization signal and output a second optical power signal representing the optical power of the second polarization signal; and a controller configured to control the polarization controller on the basis of the first optical power signal and the second optical power signal.

Abstract: Apparatus and methods for receiving and processing optical signals carrying symbols that represent data, including an optical receiver having fractional sampling analog-to-digital conversion and interpolation timing recovery synchronization for processing an optical signal.

Abstract: By using low-frequency signals, an optical transmitting unit modulates one of a wavelength, a transmission timing, and an intensity of light as a carrier wave. A polarization multiplexer synthesizes the output light signals, modulated by the optical transmitting unit, in polarization states orthogonal to each other and generates polarization-multiplexing signals. A polarization splitter splits by extracting two orthogonal polarization components from the polarization-multiplexing signals. The polarization states of the polarization-multiplexing signals are controlled by a polarization controller in an optical receiving unit. A band-pass filter extracts components transmitting through passbands from output signals of the optical receiving unit and outputs an intensity of the components.

Abstract: Methods, systems, and devices are described for a digital demodulator device for processing received optical signals. The device may include a quadrature error filter that receives a digitized version of an optical signal, and removes quadrature errors to generate a filtered series of data samples. The device may also include a frequency offset removal module for performing frequency rotation on the filtered series of data samples. The device may include a chromatic dispersion compensation module which removes chromatic dispersion from horizontal and vertical polarization channels. The device may include a polarization mode dispersion (PMD)/polarization dependent loss (PDL) compensation module which compensates for interference caused by PMD and PDL. The device may also include a phase recovery module configured to track and correct phase.

Abstract: Polarization mode dispersion (PMD) in a dual-pole optical communications network is compensated for using an adaptive PMD equalizer. The PMD equalizer may include a number of substantially identical filter modules that provide partial outputs which may be combined to form a PMD compensated output. A constant modulus algorithm (CMA)-based equalizer may track PMD across both poles and generates an error signal. The CMA-based equalizer includes a filter bank, and uses an update algorithm and tap/output adjustments based on a difference between combined tap energies and an index, and feedback from a forward error correction code frame synchronizer.

Abstract: In an optical transmission system including a transmitter Tx and a receiver Rx connected via a fiber link F, where the receiver Rx is adapted to utilize Forward Error Correction (FEC) on received signals, a polarization scrambler is provided at the transmitter Tx to scramble the polarization state of a transmitted signal, a polarization delay line is provided at the receiver Rx for controlling the polarization mode dispersion induced distortion of a received signal, a feedback unit is provided at the receiver Rx for providing a feedback signal based on at least part of the received signal, and at least one polarization controller interconnects the fiber link F and the polarization delay line. The polarization controller is operable based on the feedback signal to mitigate the polarization mode dispersion of the signal.

Abstract: In accordance with one embodiment of the present disclosure, a system for optical signal dispersion and parameter monitoring comprises a tunable filter configured to filter a portion of one channel of an optical signal. The system comprises a polarization beam splitter configured to split the portion into first and second polarization beams and further comprises first and second photodetectors configured to respectively convert the first and second polarization beams into first and second electrical signals. Also, the system comprises a control unit configured to determine optical dispersion in the portion based on the first and second electrical signals when the portion includes a test signal. The control unit is configured to determine optical signal parameters of the portion such as channel power, channel wavelength, optical spectrum analysis (OSA) and optical signal-to-noise ratio (OSNR) based on the first and second electrical signals when the portion does not include the test signal.

Abstract: 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.

Abstract: A plurality of optical transmission sources data provides data communication from a transmitting module to a common detector cooperative with a receiving module, the modules being subject to relative rotation about a shared axis. The detector can be located on the shared axis, each of the sources directing a beam onto the detector regardless of relative module orientation, and/or the light can be diffused, so that it is detected regardless of source and detector placement and relative module orientations. Transmissions can be distinguished according to synchronized timing, differing optical frequencies, differing baud rates, and/or differing circular polarizations. The detector can split the light into a plurality of beams which pass through different optical filters and are thereby distinguished. Cut-off circuits can prevent failed sources from transmitting.

Abstract: Coherent optical signal processing is performed in a coherent receiver (or diagnostic/testing apparatus) that converts an amplitude and/or angle-modulated optical signal into two electrical signals. A simple receiver can only detect one phase of the signal and only the polarization that is aligned with a local oscillator laser polarization. To detect both phases and both polarizations, two sets of two interferometers, one each with a ?/2 phase shift are required. Coherent optical signal processing methods, apparatus, techniques, etc. are disclosed that include individual components comprising a polarization combiner, a Savart device and photodetection apparatus with substantially reduced temperature and alignment sensitivity operating in optical communication systems and/or subsystems. The various embodiments can be used alone or in such combinations to provide improved coherent optical signal processing in a receiver.

Abstract: A method and apparatus for clearing an optical channel for transmitting data through free space between a first and second location includes a light beam, wherein the light beam has a spatially and/or time-dependent modulated intensity profile, and is substantially collimated so that the intensity profile is conserved over a specified distance of operation. The light beam includes a cross-sectional profile having regions of low and high intensity, portions of which are provided for the transmission of an optical data signal. A light source wavelength and intensity are selected for types of obscurant particles having optical properties whereby the radiation pressure acts on the particles, and the particles may then be either attracted into or repelled from portions of the spatially modulated optical beam, leaving certain portions of the optical channel beam absent of obscurant particles, thereby enabling transmission of optical data through the cleared optical channel with low attenuation.

Abstract: A receiver and method are provided. The receiver includes a detector configured to receive polarization multiplexed coded orthogonal frequency division multiplexing input sequences and generate estimates of unknown transmitted symbols in the input sequences for x- and y-polarization channels with respect to laser phase noise and PMD. A demapper coupled to the detector is configured to partially cancel polarization mode dispersion (PMD) in the input sequences by computing symbol probabilities for the estimates with respect to the laser phase noise, and averaging the symbol probabilities with respect to the laser phase noise. One or more low-density parity-check (LDPC) decoders coupled to the demapper are configured to receive bit probabilities derived from the averaged symbol probabilities and output code words based at least on the bit probabilities. The one or more LDPC decoders iteratively provide extrinsic soft information feedback to the demapper to compensate for the PMD.

Abstract: The present invention relates to an optical receiver, and particularly, to an optical receiver by which a DQPSK-modulated optical signal is demodulated to a multilevel phase-modulated signal.

Abstract: With respect to a coherent optical receiving apparatus, a polarization multiplexing light signal, whereupon a first signal is placed upon a first polarized wave light and a second signal is placed upon a second polarized wave light, is polarization divided upon the transmitting side thereof, and the first signal and the second signal cannot be received in correspondence with the transmitting side. Accordingly, disclosed is a coherent optical receiving apparatus, comprising a coherent light receiving unit that detects coherent light, and a signal processing unit that carries out signal processing that is set with control coefficients. The coherent light receiving unit receives a first polarized light that is modulated with a first transmitted signal and outputs a first detected signal, and simultaneously receives the first polarized light with a second polarized light that is modulated with a second transmitted signal, and outputs a second detected signal.

Abstract: Excitation light is split into two components with mutually orthogonal polarization. One component is fed clockwise and the other component is fed counterclockwise into a polarization maintaining loop. A second-order nonlinear optical medium disposed in the loop generates up-converted light from each excitation component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down conversion. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation or down-converted components. The clockwise and counterclockwise components of the down-converted light are recombined and output as quantum entangled photon pairs having substantially the same wavelength as the excitation light. The optical components can be optimized for operation at this wavelength without the need to consider the shorter wavelength of the up-converted light.

Abstract: For readjusting a polarization drift in the transmission of a polarization-encoded optical signal from a transmitter via a light guide to a receiver, optical auxiliary signals having the same wavelength as the polarization-encoded signal as well as different polarizations as in correspondence with a first base and a second base are fed into the light guide on the side of the transmitter while the transmission of the polarization-encoded signal is interrupted, and the optical auxiliary signals are picked up from the light guide and checked for shifts of the different polarizations by a polariometer on the side of the receiver, whereupon, in the event of the detection of polarization shifts, the different polarizations shifted during the transmission are displaced in the sense of the polarization set values via a polarization controller associated with the light guide.

Abstract: In a coherent optical receiver of an optical communications network, a method of recovering a clock signal from a high speed optical signal received through an optical link. A set of compensation vectors are adaptively computed for compensating Inter-symbol Interference (ISI) due to at least polarization impairments of the optical signal. A channel delay is estimated based on the computed compensation vectors. The estimated channel delay is subtracted from the computed compensation vectors to generate corresponding modified compensation vectors. Finally, the modified compensation vectors are used to derive a recovered clock signal.

Abstract: In accordance with the present disclosure a system for reducing polarization dependent loss (PDL) of an optical signal comprises a delay module coupled to one or more PDL inducing network elements of an optical network. The delay module is configured to time interleave a first polarization component with respect to a second polarization component of the optical signal. The time interleaving reduces interference caused by cross-talk components associated with the first and second polarization components and induced by the PDL of the PDL inducing elements.

Abstract: In accordance with the present disclosure a method for reducing polarization dependent loss experienced by an optical signal comprises monitoring a power level of a polarization multiplexed optical signal. The method further comprises detecting a power spike based on the monitored power. The power spike is induced by misalignment of a polarization component axis of the optical signal with a polarization dependent loss (PDL) axis of one or more network elements. The method further comprises rotating the polarization orientation of the optical signal such that the power spike is reduced.

Abstract: In a coherent optical receiver of an optical communications network, a method of recovering a clock signal from a high speed optical signal received through an optical link. A set of compensation vectors are adaptively computed for compensating Inter-symbol Interference (ISI) due to at least polarization impairments of the optical signal. A channel delay is estimated based on the computed compensation vectors. The estimated channel delay is subtracted from the computed compensation vectors to generate corresponding modified compensation vectors. Finally, the modified compensation vectors are used to derive a recovered clock signal.

Abstract: A handheld device (310) includes: a transmitter or receiver (410) of a signal beam (340) for quantum key distribution; and a source (412, 414) of alignment beams (312, 314, 316, 318) that diverge from each other in a pattern that matches sensors (322, 324, 326, 328) on a station (320) containing a receiver or transmitter (430) for the quantum key distribution. The alignment beams from the handheld device (310) are of sufficient intensity to produce on the station visible spots that facilitate manual alignment of the handheld device (310). The station (320) can measure a position and a direction of respective alignment beams and dynamically steer the signal beam (340) according to the measurements.

Abstract: Provided are an auto-compensating quantum cryptography transceiver and method of transmitting a quantum cryptography key at a high speed. A quantum cryptography transmitter includes a wavelength converter, an optical attenuator, an optical phase modulator, and a Faraday mirror. A quantum cryptography receiver includes a polarization beam splitter, an optical coupler, an optical filter, and a photon detector. Thus, a limit of a transmission rate caused by Rayleigh scattering of an optical fiber can be overcome.

Abstract: A polarization-tracking device having a waveguide grating that serves as a polarization splitter and an optical fiber-to-waveguide coupler. The polarization-tracking device also has an optical mixing circuit configured to receive light from the waveguide grating and a control circuit for tuning the optical mixing circuit. Based on an optical feedback signal received from the optical mixing circuit, the control circuit can configure the latter to produce two optical output signals that represent, e.g., two independently modulated polarization components of a polarization-multiplexed optical input signal or two principal states of polarization of an optical input signal that has been subjected to polarization-mode dispersion. Certain embodiments of the polarization-tracking device lend themselves to convenient implementation in a photonic integrated circuit and are configurable to provide endless polarization control.

Abstract: In a polarization multiplexed optical transmitting and receiving apparatus, output light from a light source section of a transmission unit is separated in a polarization separating section, and then modulated in first and second modulation sections, and the modulated lights are synthesized in a polarization synthesizing section, and transmitted to an optical transmission line. Then the polarization multiplexed light propagated through the optical transmission line is demodulated in a reception section of a reception unit, and together with this, transmission characteristic information of the reception light is transferred to the transmission unit. The transmission unit that receives the transmission characteristics information controls a delay section that adjusts a delay amount of relative phases of drive signals of the modulation sections, so that the transmission characteristics of the polarization multiplexed light are within an allowable range.

Abstract: An optical transmission/reception device includes at least one light emitting portion and at least one light receiving portion on the same substrate. The light emitting portion includes at least a lower multilayer reflector and an active layer provided on the lower multilayer reflector. A metal layer including a plurality of opening portions is provided in an upper portion of the light emitting portion. Each of the opening portions has a size smaller than a light emission wavelength of the light emitting portion.

Abstract: The invention relates to an apparatus and a method for modulation of an optical signal with a data signal, said apparatus (6) comprising a configurable digital encoding unit (8) encoding data of said data signal to provide an encoded modulation control signal (EMCS), and a signal modulation unit (9) modulating said optical signal with respect to its signal phase and/or signal amplitude in orthogonal polarization directions in response to said encoded modulation control signal (EMCS) to generate a multi-dimensional optical signal vector.

Abstract: According to one embodiment, an optical receiver adapted to recover OOK or PAM data carried by a modulated optical carrier has an optical detector adapted to produce a sequence of vector pairs having first and second digital vectors indicative of complex values of first and second polarization components, respectively, of the modulated optical carrier at a corresponding sampling time. The optical receiver also has a digital processor that is connected to receive the sequence and is adapted to perform a rotation on each pair in a manner that tends to compensate for polarization rotation produced by transmitting the modulated optical carrier from an optical transmitter thereof to the optical receiver. The digital processor is further adapted to estimate values of the OOK or PAM data encoded onto each of the first and second polarization components based on the vectors produced by the rotation in a manner responsive to values of energy errors in the estimated values.

Abstract: The present invention discloses a system for signalling within optical or combined optical/electronic networks wherein a first transmission node executes polarization multiplexing on transmitted traffic, and at one or more intermediate nodes one or more of the following processes are carried out on the sent traffic: demultiplexing by polarization and/or polarization and/or SOP-alignment. Further a method for packet handling within optical packet switched networks where, at a first transmission node carries out polarization demultiplexing of transmitted traffic, and at one or a number of intermediate nodes carries out one or more of the following processes on the transmitted traffic; demultiplexing by polarization, and/or polarization and/or SOP-alignment. Said separation into states of polarization is used in separation of QoS-classes.

Abstract: Devices, systems and techniques for optical communication are provided based on polarization division multiplexing (PDM) to use an optical monitor channel at a distinct optical monitor wavelength to monitor optical polarization fluctuation and polarization mode dispersion during the transmission from the transmitter to the receiver to facilitate the effective demultiplexing of the two orthogonal signal channels at the receiver through automatic feedback control on a dynamic polarization controller and a polarization beam splitter.

Abstract: The present invention provides a system, apparatus and method to control an optical polarization beam splitter. A portion of an optical output of the polarization beam splitter is converted into a corresponding electrical signal. The electrical signal is then provided to the polarization beam splitter as a control signal via a feedback loop. The polarization beam splitter controls a characteristic of the optical output of the polarization beam splitter in response to the received control signal. The characteristic, for example, may be controlled through thermo-optically or electro-optically. The control system may be used over a period of time to maintain the characteristic at a desired value, for example as the components of the polarization beam splitter, or other elements used in the control of the polarization beam splitter, age.

Abstract: In various embodiments, a secure optical communication system is disclosed. Such a system may include a photon-pair generation circuit configured to generate pairs of photons with each photon pair including a first-channel photon and a second-channel photon, a transmitting circuit configured to receive first-channel photons, and modulate the first-channel photons according to a stream of data using a first optical circulator to produce first-modulated photons, and a receiving circuit configured to receive second-channel photons, pass the second-channel photons through a complementary optical circulator to produce second modulated photons, and detect relative timing between the first-modulated photons and the second modulated photons to recover the stream of data.

Abstract: The invention provides an apparatus and method for time delaying different polarization components of a signal relative to one another, comprising a polarization signal splitter which splits first and second polarization components of an input signal into a first component signal and a second component signal such that said first component signal propagates along a first path and the second component signal propagates along a second path, wherein said first component signal reaches a location relative to when said second component reaches said location at times differing by a delayed time, and use of the apparatus in a communication system. The apparatus may be used for quantum cryptography, to convert a sender's polarization-qubit signal into a signal appropriate for channels and receivers based on phase-encoded schemes.

Abstract: A high-speed optical transmitter comprises multiple digital lanes that are provided to a bank of digital-to-analog converters. The analog signals are then used to Phase Shift Keyed (PSK) modulation using a Chirp Managed Laser (CML)-based transmitter, and potentially using dual polarization. A corresponding optical receiver receives the sequence of optical signals at a demodulator. For each polarization, the demodulator includes a corresponding demodulation channel that is configured to demodulate that polarization component of the optical signal into one or more signal components. Each of these signal components is converted into a corresponding digital signal using a corresponding analog-to-digital converter. In the case of higher-order PSK modulation (e.g., 8PSK or higher), for each polarization, the analog converter has a lower sampling rate than for QPSK modulation.

Abstract: In the field of communication and transmission, a method and a device for receiving an OPFDM-DQPSK signal are provided. The device includes a power splitter, adapted to split the OPFDM-DQPSK signal into two beams of signals; a polarization beam splitter (PBS), adapted to splitting one of the two beams of signals into a first signal and a second signal; a demultiplexer (Demux), adapted to demultiplex the other beam of signal to obtain a third signal and a fourth signal; two delayers, adapted to delay the third signal and the fourth signal respectively; a first frequency-mixing receiving module, adapted to perform frequency-mixing receiving on the first signal and the delayed third signal; a second frequency-mixing receiving module, adapted to perform frequency-mixing receiving on the second signal and the delayed fourth signal; and a decision recovery module, adapted to recover four logical sequences by performing decision on the four electrical signals.

Abstract: The present invention provides a system and method of optical communications that utilize coherent detection technique and optical orthogonal frequency division multiplexing for phase encoded data transmission. In particular the invention addresses a device and method for digital polarization compensation of optical signals with up to 100 Gb/s transmission rate received via an optical link. The polarization compensation operates in two modes: acquisition mode and tracking mode. The polarization recovery is performed at the receiver side using the received digital signal conversion into frequency domain and separate reconstruction of the polarization state in each spectral component.

Abstract: Methods and systems for PMD compensation in an optical communication system are implemented by transmitting multiple optical signals through a common optical conduit to an optical compensator that adjustably rotates the polarization states of the multiple optical signals and transmits the rotated optical signals to an optical receiver. The receiver, upon sensing an excessive error condition, commands the optical compensator to change the polarization state of rotation, which changes the PMD profile of the received optical signals.

Abstract: A burst-mode differential phase shift keying (DPSK) communications system according to an embodiment of the present invention enables practical, power-efficient, multi-rate communications between an optical transmitter and receiver. An embodiment of the system utilizes a single interferometer in the receiver with a relative path delay that is matched to the DPSK symbol rate of the link. DPSK symbols are transmitted in bursts, and the data rate may be varied by changing the ratio of the burst-on time to the burst-off time. This approach offers a number of advantages over conventional DPSK implementations, including near-optimum photon efficiency over a wide range of data rates, simplified multi-rate transceiver implementation, and relaxed transmit laser line-width requirements at low data rates.

Abstract: In the optical transmitting system, the optical transmitter transmits a polarization combined signal light obtained by combining a pair of lights having different polarization orientation, and the optical receiver separates the combined signal light. In the optical transmitter, a polarization changer changes a state of polarization of the polarization combined signal light. In the optical receiver, a polarization reverse-changer changes the state of the polarization combined signal light in a reverse direction of the change that polarization changer applies.