Abstract: A receiver is configured to detect, at a communication interface, a received signal that suffers from degradations incurred over a communication channel. The receiver applies an adaptive filter to a series of received blocks of a digital representation of the received signal, thereby generating respective filtered blocks, where each received block represents 2N frequency bins, and where N is a positive integer. The receiver calculates coefficients for use by the adaptive filter on a jth received block as a function of (i) error estimates associated with an (j?D?1)th filtered block, where D is a positive integer representing a number of blocks, and where j is a positive integer greater than (D?1); and (ii) an inverse of an approximate covariance matrix associated with the (j?D?1)th received block, where the approximate covariance matrix is a diagonal matrix of size L×L, and where L is a positive integer lower than 2N.

Abstract: An optical transmission method for processing a signal based on direct detection includes setting, by an equalizer, an adaptive equalization coefficient by performing an equalization process during a training symbol field section in a frame of a received signal, performing, by a channel estimator, channel estimation to perform an equalization process of a soft output maximum likelihood sequence equalizer (MLSE) during the training symbol field section, driving the soft output MLSE, and compensating for, by the soft output MLSE, distortion of the received signal during a data symbol field section in the frame on the basis of the adaptive equalization coefficient and an estimated result value of a channel, and recovering, by an error corrector which allows soft-decision processing to be performed, the received signal by performing error correction on the received signal in which the distortion is compensated for.

Abstract: A photonic molecule laser is described that includes a photonic molecule waveguide coupled to a photonic molecule seeding source configured to deliver a plurality of photonic molecules. The photonic molecule waveguide includes a second dopant maintained at a population inverted state with an energy level transition corresponding to a second frequency that is an N-fold multiple of a first frequency and amplifies the number of photonic molecules via stimulated emission. The photonic molecule seeding source includes a waveguide with a first dopant maintained at a population inverted state with an energy level transition corresponding to the first frequency. A pump source is coupled to the waveguide configured to deliver a first frequency laser pulse with pulse coherence time less than the photonic molecules correlation time. Each photonic molecule includes a threshold bound state of N first frequency photons, and each photonic molecule has the second frequency.

Abstract: A receiving apparatus includes a first processor configured to compensate, in a perturbation back-propagation (PBP) scheme, waveform degradation of an optical signal by traveling an optical transmission line due to a nonlinear optical effect; a memory; and a second processor coupled to the memory and the second processor configured to change a gamma coefficient to be used in the PBP scheme, measure reception quality of the optical signal for each of gamma coefficients obtained by the changing, specify a gamma coefficient in accordance with the reception quality from among the gamma coefficients obtained by the changing, and set the specified gamma coefficient as a parameter of the PBP scheme.

Abstract: Proposed is a method of receiving a WDM optical upstream signal in an optical access network. The WDM signal is filtered using a first optical filter yielding a first filtered signal. The first optical filter has a flat-top shaped pass-band transfer function. Furthermore the WDM signal is filtered using second optical filter yielding a second filtered signal. The second optical filter has a pass-band transfer function that is strictly monotonically increasing for wavelength values below a center wavelength of the transfer function and that is strictly monotonically decreasing for wavelength values above the center wavelength of the transfer function. Received upstream data is derived from the first filtered signal. An optical signal power level is derived from the second filtered signal an optical signal power level. Finally, it is indicated to an optical network unit a desired direction of wavelength shift in dependence on the derives signal power level.

Abstract: A method (10) of non-linear propagation impairment equalization, the method comprising the steps of: a. receiving (12) communications traffic carried by an optical communications signal transmitted over an optical communications link; b. generating (14) a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link; and c. applying (16) the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalized communications traffic. An optical communications link nonlinear propagation impairment equalizer and optical communications signal receiver apparatus are also provided.

Abstract: The filter estimate produced by post-equalization processing of an optical signal at a receiver is used to generate pre-equalizer filter coefficients that are communicated back to the source of the optical signal for performing pre-equalization. In one advantageous aspect, the already existing post-equalization modules of an optical receive equipment can thus be used to produce, in addition, a pre-equalizer filter for use by the source side.

Abstract: For determining equalization parameters for performing equalization for optical signals transmitted by a first device to a second device via an optical band-pass filter, the second device being configured for receiving optical signals output by said optical band-pass filter and transmitted by the first device on a carrier wavelength when said carrier wavelength is comprised in the passband of the optical band-pass filter, said carrier wavelength and/or said passband of the optical band-pass filter being a priori unknown, a monitoring device performs: determining information representative of a level of detuning between the carrier wavelength of the optical signals and the nominal wavelength of the optical band-pass filter; and determining said equalization parameters, on the basis of said determined information representative of the level of detuning between the carrier wavelength of the optical signals and the nominal wavelength of the optical band-pass filter.

Abstract: A method to process applicable to coherent optical channels with either linear or nonlinear phase noise includes: splitting a received sequence of data into clusters of points according to a cumulative log-likelihood function from constellation obtained in a previous iteration; generating new constellation points by calculating a center of mass of the clusters of points; repeating until convergence or until a predetermined number of iterations has been reached to determine a signal constellation; and transmitting signals over the coherent optical channels with nonlinear phase noise using the disclosed signal constellation and LDPC-coded modulation concepts.

Abstract: An optical transmission system includes: a first optical transmission device configured to transmit measurement light to an optical transmission line on a first direction; and a second optical transmission device configured, when an optical transmission characteristic is measured, to loop-back the measurement light received from the first optical transmission device through an optical transmission line on the first direction and to transmit the measurement light to the first optical transmission device through an optical transmission line on a second direction, wherein, when the optical transmission characteristic is measured, the first optical transmission device receives the measurement light loop-backed by the second optical transmission device and measures the optical transmission characteristic between the first optical transmission device and the second optical transmission device.

Abstract: A method and a device for conveying optical data are provided, wherein an optical network unit conveys data to a terminal via dual sideband modulation, wherein the terminal processes only the upper or only the lower sideband received from the optical network unit, and wherein several dual sideband modulated signals from several optical network units partially overlap when being received at the terminal. Furthermore, a communication system is suggested comprising at least one such device.

Abstract: An optical signal generation unit (110) generates an optical signal for transmission by adding modulation based on a driving signal to a carrier wave. A filtering unit (120) performs a filtering process on the driving signal. The filtering unit (120) may perform time domain equalization, and may perform frequency domain equalization. Specifically, the filtering unit (120) performs a filtering process on the driving signal, and thus sets a peak value of a power spectral density of the optical signal for transmission to be equal to or less than a second reference value while an integrated value obtained by integrating the power spectral density of the optical signal for transmission in a frequency direction is maintained at equal to or greater than a first reference value.

Abstract: A method includes evaluating an optical signal spectrum for estimated filtering parameters of an optical spectral filtering device for shaping optical signal spectrum, determining a feedback for fine tuning the optical spectral filtering device for nonlinearity tolerance enhancement in the optical transmission system, responsive to received optical signal quality in the optical signal spectrum; and using the feedback to adjust said optical spectral filtering device for predetermined shaping and predetermined fiber nonlinearity tolerance in the optical transmission system.

Abstract: Methods and systems for decoding a signal include compensating for impairments in a received signal using at least carrier phase estimation, where residual phase error remains after compensation; calculating symbol log-likelihood ratios (LLRs) for symbols in the compensated signal using Monte Carlo integration; demapping the symbols in the compensated signal using the symbol LLRs and extrinsic information from signal decoding to produce one or more estimated codewords; and decoding each estimated codeword with a decoder that generates a decoded codeword and extrinsic information.

Abstract: A system and method for blind equalization of a QAM signal. Equalization is achieved using an algorithm characterized by cost function that is a function the Euclidian distance, e.g. the minimum Euclidian distance, between points of the constellation associated with the QAM signal, i.e. the distance between symbols.

Abstract: Methods, systems, and devices are described for modulating and demodulating data on optical signals. During modulation, at least one stream of symbol mapped bits is filtered with at least one pulse shaping filter to reduce a bandwidth of the stream of bits and to pre-compensate for at least one identified non-ideal transmission condition. The filtered bits are modulated onto a waveform in the digital domain, and the modulated filtered bits are transmitted to digital-to-analog converter. The output of the digital-to-analog converter is converted to an optical signal. During demodulation, a received optical signal is sampled at a first sampling rate at an ADC, downsampled to a lower sampling rate for filtering, filtered with at least one discrete pulse-shaping filter, upsampled for equalization and demodulation, and then equalized and demodulated.

Abstract: The present invention provides a wavelength division multiplexing system and a method and device for its residual dispersion compensation, wherein the device for residual dispersion compensation of wavelength division multiplexing system comprises: a performance parameter detecting device for receiving and detecting performance parameter of receiving terminal optical signal and sending detecting result of the performance parameter to a central control device; the central control device for deciding a dispersion regulating mode of a tunable dispersion compensator according to the detecting result of the performance parameter and sending the dispersion regulating mode to a tunable dispersion compensator control device through control signaling; and the tunable dispersion compensator control device for receiving the control signaling sent by the central control device and adjusting dispersion compensation amount of the tunable dispersion compensator according to the control signaling in order to make residual di

Abstract: The present wavelength multiplexed optical system includes a multimode optical fiber that transmits wavelength multiplexed optical signals and a plurality of multimode modal dispersion compensation optical fibers. Each modal dispersion compensation optical fiber can transmit one of the multiplex wavelengths, and each modal dispersion compensation optical fiber has an optimized index profile such that the modal dispersion for the transmitted wavelength is approximately inversely equal to the modal dispersion induced in the multimode optical fiber. The wavelength multiplexed optical system facilitates an increased bitrate without reducing bandwidth.

Abstract: An embodiment of the invention is a technique to equalize received samples. A coefficient generator generates filter coefficients using an error vector and input samples. A filter stage generates equalized samples from input samples using the filter coefficients. The received samples are provided by a receiver front end in an optical transmission channel carrying transmitted symbols. Other embodiments are also described.

Abstract: Exemplary embodiments include a method and systems for impairment compensation in a communication system. The systems can include an electronic phase conjugation system that receives an incoming optical signal from a first section of a fiber optic link, converts the incoming optical signal to an in-phase electric signal and a quadrature electrical signal, and generates a phase conjugated outgoing optical signal from the in-phase and quadrature electrical signals. The phase conjugated outgoing optical signal compensates for impairment of the fiber in the communication system.

Abstract: An embodiment of the invention includes a tunable optical dispersion compensator (TODC) comprising a first beam displacer on an optical path, wherein the first beam displacer separates an optical signal into a first beam and a second beam, and one or more polarizing beam splitters on the optical path, wherein the one or more polarizing beam splitters keep the first beam and the second beam on the optical path. The TODC also comprises one or more etalons on the optical path, wherein the one or more etalons are tunable to introduce a group delay in the first beam and the second beam, and a reflecting mirror on the optical path, wherein the reflecting mirror returns the optical signal back along the optical path. The TODC further comprises a second beam displacer, wherein the second beam displacer combines the first beam and the second beam into an output optical signal.

Abstract: Methods, apparatuses, and systems are presented for performing adaptive equalization involving receiving a signal originating from a channel associated with inter-symbol interference, filtering the signal using a filter having a plurality of adjustable tap weights to produce a filtered signal, and adaptively updating each of the plurality of adjustable tap weights to a new value to reduce effects of inter-symbol interference, wherein each of the plurality of adjustable tap weights is adaptively updated to take into account a constraint relating to a measure of error in the filtered signal and a constraint relating to group delay associated with the filter. Each of the plurality of adjustable tap weights may be adaptively updated to drive group delay associated with the filter toward a target group delay.

Abstract: An optical network contains dispersion compensation modules with Fiber Bragg Gratings. A photo detector behind the Fiber Bragg Grating detects the not reflected rest of the gratings input signal and therefore the dispersion compensation modules input signal. This information is used to reduce the expenditure and to avoid errors of configuration or administration of the dispersion compensating subsystem of the optical network.

Abstract: A digital filter processes an input signal to be conveyed through an optical communications system. The processing generates a predistorted signal using a compensation function that mitigates impairments of the optical communications system. The input signal has a sample period of T, while the predistorted signal has a sample period of T/2. The digital filter has a first branch including a respective first T-spaced filter for processing the input signal using the compensation function to generate a corresponding first output signal comprising nT/2 samples with n odd. A second branch includes a respective second T-spaced filter for processing the input signal with a delay of T relative to the first branch using the compensation function to generate a corresponding second output signal comprising nT/2 samples with n even. A combiner operates to combine the first and second output signals to generate the predistorted signal having a sample period of T/2.

Abstract: A time domain filter receives a double sideband (DSB) input in the frequency domain and compresses this input into a time domain signal filtered by a time gate for providing a time filtered signal that is then expanded back into the frequency domain as a single sideband (SSB) output with one sideband being filtered by the time gate for translating DSB signals into SSB signals well suited for communicating chirped modulated signals as SSB signals along an electrical line or optical fiber without dispersive nulling of the communicated signal.

Abstract: An optical receiver according to the invention includes a polarization diversity unit receiving a polarization multiplexed optical signal obtained by multiplexing two optical signals having a same frequency band of carrier waves and polarization states orthogonal to each other, and a frequency domain equalization unit receiving signal components parallel to mutually orthogonal polarization axes from the polarization diversity unit, wherein the frequency domain equalization unit includes filters for which filter coefficients thereof are set for compensating degradation of transmission characteristics in one optical signal without polarization multiplexing by means of the frequency domain equalization.

Abstract: The present invention provides an updating apparatus and method for an equalizer coefficient, receiver and optical communication system. The updating method comprises: receiving an optical signal transmitted by a transmitter in an optical communication system, the optical signal comprising transmission data and a constant modulus signal for updating a coefficient of an equalization filter; performing coherent detection and analog-to-digital conversion on the optical signal, so as to obtain a digital electric signal; and updating the coefficient of the equalization filter at a symbol corresponding to the constant modulus signal in the digital electric signal. With the embodiments of the present invention, not only the coefficients of the equalizer may be optimized, but also being adapted to signals in various modulation formats, and the complexity of the channel equalization may be lowered as well.

Abstract: A system is provided for electrical domain optical spectrum shaping. The system may include a laser, a modulator, a first electrical filter, and a second electrical filter. The laser may be configured to output an optical carrier signal. The modulator may be configured to modulate the optical carrier signal to output a modulated optical signal based on a first filtered input signal and a second filtered input signal received by the modulator. The first electrical filter may be configured to filter a first input signal to produce the first filtered input signal. The second electrical filter may be configured to filter a second input signal to produce the second filtered input signal.

Abstract: A light reception device includes: an interferometer that outputs a signal obtained by making an optical phase modulated signal interfere with a reference signal after shifting an optical phase of the optical phase modulated signal by a given amount; a light reception element that receives an output signal from the interferometer and converts the output signal into a light reception current; and a phase controller that controls a control amount in controlling the given amount so that a value of a function, which is calculated based on an amount relating to the light reception current and a change amount of an amount relating to the light reception current against the control amount, becomes an extreme value or 0.

Abstract: A method of generating an optical radiation signal is to be implemented by an optical radiation signal generating device including a dual beam generating unit for receiving an original optical input signal, and a second-order fiber Bragg grating (FBG). The dual-beam generating unit is configured to generate, from the original optical input signal, first and second optical input signals having a phase difference therebetween. The second-order FBG is configured to receive the first and second optical input signals, and to radiate an optical radiation signal by interference between the first and second optical input signals.

Abstract: An equalization filter is provided for solving the problem in which there is a limited range in which compensated for distortion of a transmission signal can be made. Measuring instrument 104 measures a distortion quantity which characterizes distortion of the transmission signal. Comparator 105a generates a differential signal which indicates the difference between the transmission signal and a compensation signal. Delay device 105b delays the differential signal based on the distortion quantity measured by measurement instrument 104 and generates the compensation signal.

Abstract: It is an object of the present invention to provide an optical waveform shaping device of high resolution. The above-mentioned problem is solved by an optical waveform shaping device (10) comprising a branching filter (11) for dividing the light beam from a light source into light beams of each frequency, a condensing part (12) for condensing a plurality of light beams divided by the branching filter (11), a polarization separation means (13) for adjusting the polarizing planes of the light beams having passed through the condensing part (12), and a spatial light modulator (14) having a phase modulation part and an intensity modulation part where the light beams having passed through the polarizing plate (13) are incident.

Abstract: A device may include a group delay monitor and a signal receiver. The group delay monitor may be configured to obtain group delay data corresponding to group delay of an optical signal and provide the group delay data to a signal receiver. The signal receiver configured to obtain a time-domain digital signal corresponding to the optical signal, convert the time-domain digital signal into a frequency-domain signal, apply a digital filter constructed based on the group delay data to the frequency-domain signal to obtain an output signal, and transmit the output signal.

Abstract: A dispersion compensating apparatus includes a tunable dispersion compensator that dispersion-compensates an optical signal using a group delay property that is asymmetrical in bands outside an effective band; a set device that sets a dispersion compensation amount in the tunable dispersion compensator; and a shifter that shifts a central frequency of the effective band of the tunable dispersion compensator, based on the dispersion compensation amount set by the set device.

Abstract: A filter-based method of demodulating differentially encoded phase shift keyed (DPSK) optical signals, such as commonly used binary-DPSK (DBDPSK) and quadrature DPSK (DQPSK) signals, that can achieve optimal receiver sensitivity is described. This approach, which combines filtering and differential phase comparison, can reduce the complexity and cost of DPSK receivers by obviating delay-line interferometer-based demodulation. This can improve receiver stability and reduce size, weight, and power, while maintaining the ability to achieve optimal communications performance.

Abstract: Embodiments for optical communication are provided in which a receiver includes a digital signal processor configured to process a digital form of an input signal. In one embodiment, the digital signal processor includes a first electronic chromatic dispersion compensation module for compensating the digital form of the input signal, at least one nonlinearity compensation stage for serially compensating an output of the electronic chromatic dispersion compensation module; and a second electronic chromatic dispersion compensation module for compensating an output of the at least one nonlinearity compensation stage.

Abstract: An optical communication system combines strong electrical pre-filtering of data at the transmitter and digital feedback equalization (DFE) at the receiver to enhance spectral efficiency. The system can be applied to optical networking and digital communication systems, including binary modulated systems optical network systems.

Abstract: Systems and methods for extended reach low differential latency optical networking with optical amplifiers and dispersion compensation modules configured to minimize latency between transmit and receive paths are provided. Additionally, systems and methods are provided for incorporating absolute time references wherein the relative accuracy of clock time between various servers used in various multi-site enterprises is required. The transport systems and methods are used in conjunction with low differential latency systems. The transport systems and methods provide that the differential latency between transmit and receive directions is maintained within about +/?5 microseconds of the transmit/receive path differential delay requirement in order to perform within the overall parameters of the low differential latency system architecture.

Abstract: An embodiment of the invention is a technique to equalize received samples. A coefficient generator generates filter coefficients using an error vector and input samples. A filter stage generates equalized samples from input samples using the filter coefficients. The received samples are provided by a receiver front end in an optical transmission channel carrying transmitted symbols. Other embodiments are also described.

Abstract: An all-optical modulation format converter for converting optical data signals modulated in an on-off-keying (OOK) format to a phase-shift-keying (PSK) format. The OOK-to-PSK converter can be coupled to a delay-line interferometer to provide an all-optical wavelength converter for differential PSK (DPSK). The OOK-to-PSK converter can also be used in all-optical implementations of various functions, including, for example, exclusive-OR (XOR/NXOR) and OR logic, shift registers, and pseudo-random binary sequence (PRBS) generators. Several variants of all-optical devices are described.

Abstract: A light dispersion filter is composed of three or more optically transparent layers each having a value equal to the value of the product of the refractive index and thickness of the optically transparent layer and transmitted light, and a plurality of partially reflective layers arranged alternately with the optically transparent layers and having predetermined reflectivities. Alternatively, a light dispersion filter has a plurality of etalon resonators which are arranged in series such that the value of the product of the refractive index of air and the interval of the etalon resonators is equal to the value of the product of the refractive index and thickness of the optically transparent layers.

Abstract: A distortion compensator, an optical receiver and a transmission system including an operation selectively compensating for linear waveform distortion exerted on an optical signal via a plurality of distortion compensators and compensating for nonlinear waveform distortion exerted on the optical signal using nonlinear distortion compensators.

Abstract: An optical dispersion compensator including a first optical device in which light inputted from a first port is outputted from a second port and light inputted from the second port is outputted from a third port, an optical filter type dispersion compensation device that receives light from the second port of the first optical device and compensates wavelength dispersion with respect to the received light, and a second optical device that includes a fourth port to which light is inputted from the optical filter type dispersion compensation device, and in which the light inputted from the fourth port is outputted from a fifth port and light inputted from a sixth port is outputted from the fourth port.

Abstract: A dynamic gain equalizer-monitor (DGEM) includes a light modulator operable to modulate one or more component wavelengths of an input optical signal. The DGEM also includes a grating operable to receive one or more modulated component wavelengths from the light modulator. The grating is also operable to combine a first portion of each of the one or more modulated component wavelengths and transmit that first portion into an output optical signal. The DGEM may also include a detector array operable to receive, from the grating, a second portion of modulated component wavelengths that are separated from the first portion by the grating. The detector array is operable to generate an electrical signal proportional to an optical characteristic associated with each of the modulated component wavelengths of the second portion.

Abstract: An optical transmission system for transmitting an optical pulse in a dielectric waveguide, the system including a filter for altering a shape of the optical pulse in both amplitude and phase with respect to time so as to substantially suppress the generation of third-order nonlinearities and increase a power level of the optical pulse, the filter further providing a secure encrypted optical waveform that may be decrypted by a matching optical filter, the system allowing for energy sharing of the pulses to substantially increase system bandwidth.

Abstract: An optical reception device is provided. The optical reception device includes a filtering unit that receives input light of predetermined power, filters the input light by use of filter characteristics where the degree of attenuation of the power of an optical signal of predetermined frequency is lower than the degree of attenuation of the power of an optical signal of another frequency, and supplies an output light; and a determining unit that compares a value relevant to the power of the output light supplied by the filtering unit, with a threshold, and determines whether the input light contains signal light.

Abstract: A signal equalizer for compensating impairments of an optical signal received through a link of a high speed optical communications network. At least one set of compensation vectors are computed for compensating at least two distinct types of impairments. A frequency domain processor is coupled to receive respective raw multi-bit in-phase (I) and quadrature (Q) sample streams of each received polarization of the optical signal. The frequency domain processor operates to digitally process the multi-bit sample streams, using the compensation vectors, to generate multi-bit estimates of symbols modulated onto each transmitted polarization of the optical signal. The frequency domain processor exhibits respective different responses to each one of the at least two distinct types of impairments.

Abstract: A tunable chromatic dispersion compensation device used to compensate chromatic dispersion of wavelength of at least one predetermined wavelength band of light signal is provided. The tunable chromatic dispersion compensation device comprises a chromatic dispersion compensator, and a controller. The chromatic dispersion compensator comprises at least a first chromatic dispersion compensation unit and a second chromatic dispersion compensation unit connected with the first chromatic dispersion compensation unit in series. The first chromatic dispersion compensation unit has a free spectral range, the second chromatic dispersion compensation unit has a free spectral range same as to that of the first chromatic dispersion compensation unit. Each chromatic dispersion compensation unit comprises an interference cavity. The controller comprises an inputting unit being configured for inputting a predetermined chromatic dispersion compensation information.

Abstract: According to the WDM optical transmission system, for optical signals of respective wavelength in a WDM light propagated through a transmission path, a spectrum component at a center wavelength of each optical signal and a spectrum component in the vicinity of the center wavelength thereof are selectively attenuated by a spectrum correction optical filter, so that the WDM light is transmitted in a state where intensity of sideband components in the spectrum of each optical signal is relatively increased. As a result, even if spectrum width of the optical signal of each wavelength is limited when the WDM light passes through the band-limiting device on the transmission path, degradation of transmission characteristics caused by the attenuation of sideband components is reduced.

Abstract: A tunable dispersion compensator (TDC) is tuned from a first dispersion setpoint to a second dispersion setpoint while maintaining continuity of the dispersion. The dispersion tuning follows a pre-determined trajectory in the time domain, so that continuity of the optical dispersion across the channel optical bandwidth is maintained while minimizing all other TDC-induced optical impairments during a tuning period.