Abstract: Technology for detecting an optical data signal carried in a combined optical signal that comprises a carrier optical signal modulated by the optical data signal and also comprises ASE noise. The proposed optical data detector/receiver is provided with an SHG device adapted to generate a second harmonic optical signal of the carrier optical signal modulated by the data signal. In the signal, generated by the SHG, the ASE noise will be essentially reduced.

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: 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: Described is a method and system for reducing system penalty from polarization mode dispersion. The method includes receiving a plurality of signals at a receiving end of a transmission line, each signal being received on one of a plurality of channels of the transmission line and measuring a signal degradation of at least one of the channels of the transmission line. An amount of adjustment of a polarization controller is determined based on the signal degradation, the amount of adjustment being selected to reduce the polarization mode dispersion. The amount of adjustment is then transmitted to the polarization controller.

Abstract: In a polarization demultiplexing optical communication system (1000), an optical transmitter (100) provides a predetermined frequency deviation between carrier wave frequencies of optical signal to be transmitted, and provides a periodic fluctuation having a predetermined frequency to the light intensity of the optical signal to be transmitted. An optical receiver (300) extracts intensity information of a frequency component of the periodic fluctuation from the received optical signal, and calculates a wavelength dispersion value of the optical transmission line on the basis of the extracted intensity information. For this reason, it is possible to measure the wavelength dispersion value of the optical transmission line while operating the optical communication system.

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: An optical transmitter for generating a modulated optical signal to be transmitted over fiber optical link. The transmitter includes: an optical source for producing an optical signal; an optically linearized modulator (OLM) as external modulator for modulating the optical signal produced by the optical source with an information carrying signal. The external modulator includes a first input port for receiving a first DC bias signal, and a second input port for receiving a second DC bias signal. The optical transmitter further includes a pilot tone generator for generating a first pilot signal to be applied to the first input port and a second pilot signal to be applied to the second input port. The first and second pilot signals are capable of producing distortion products in the modulated optical signal.

Abstract: A PPM transmitter includes an optical clock generator for generating equally-spaced optical pulses with a sampling period T; an encoder for transforming an incoming waveform U(t) into a linear combination V(t) of U(t) and a delayed output V(t?kT) according to a rule V(t)=U(t)+aV(t?kT), where k is a positive integer, V(t) is voltage generated by the encoder and a is a coefficient; and an optical delay generator for delaying optical pulses generated by the optical clock generator in proportion to the voltage V(t), such that ?tn=bV(t), where b is another coefficient and where ?tn is the amount of delay imposed by the optical delay generator. The PPM transmitter functions with a PPM receiver for communicating data without the need to transmit or otherwise provide a clock signal. The PPM receiver decodes an original series of the delayed optical pulses Q(t) and a second series Q(t?ckT) delayed by ckT where c is a coefficient.

Abstract: The optical transmission equipment includes: a demultiplexer for demultiplexing a transmitted wavelength-multiplexed optical signal to first and second optical signals; a first variable dispersion compensation unit; a second variable dispersion compensation unit; a first error detector; a second error detector; and a dispersion compensation control unit for controlling dispersion compensation amounts of the first and second variable dispersion compensation units based on the detection result of the first or second error detector. Upon detection of a signal error in the first optical signal, the first variable dispersion compensation unit is controlled to change from a first compensation amount to a third compensation amount, and the second variable dispersion compensation unit is controlled to change from a second compensation amount to a fourth compensation amount.

Abstract: An optical receiver that can receive WDM signal light in which first and second wavelength bands are combined. Within optical reception units corresponding to each channel is respectively provided tunable dispersion compensator (TDC) modules in which one wavelength band is made a design standard. When known, based on signal light channel information (wavelength, frequency, channel number) notified from outside, that signal light of the second wavelength band is being input to the receiver, then in the TDC module that performed chromatic dispersion compensation of the signal light, control is performed to shift the center frequency of the dispersion compensation range by a predetermined amount corresponding to the wavelength of the signal light. When the signal light of the first wavelength band is input, shift control of the dispersion compensation range is not performed, and the dispersion compensation range at the time of designing is maintained.

Abstract: An apparatus (PMDC) for compensating polarization mode dispersion for an optical transmission fiber (TF) for transmission of optical signals, said optical signals having a first polarization component (x pol) and a orthogonal second polarization component (y pol) comprises tuneable means (PC1, DL1, PC2, DL2) adapted to compensating said fiber polarization mode dispersion. It further comprises a feedback signal generator (FSG) adapted to generating a feedback input signal for said tuneable means (PC1, DL1, PC2, DL2) for polarization mode dispersion compensation. Said feedback signal generator (FSG) comprises polarization means for converting said transmitted optical signal to at least two optical signal components with different defined states of polarization. It has further transforming means for transforming said optical signal components into electrical signal components, wherein each electrical signal component representing one of said defined states of polarization.

Abstract: A method and apparatus for suppression of four-wave mixing using polarization control with a high power polarization maintaining fiber amplifier system. The apparatus includes a master oscillator (MO) that generates a beam; a polarization controller that receives the beam from the MO and transmits the beam with a desired polarization; a pre-amplifier that receives the beam from the polarization controller, pre-amplifies the beam, and transmits the beam; a high power fiber amplifier that receives the beam from the pre-amplifier, amplifies the beam, and transmits an output beam; and a polarization detector that detects the polarization of the output beam. The polarization detector transmits feedback to the polarization controller to ensure that the output beam components aligned with the principal birefringent axes of the high power fiber amplifier have approximately equal power.

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: Transmitter waveform dispersion penalty (“TWDP”) is decreased in a transmitter. A binary data signal is received for transmission over a channel that exhibits TWDP. The data signal is shifted less than a full clock cycle to generate at least one post cursor signal. The post cursor signal is subtracted from the data signal to generate a transmitter output data signal for transmission over the channel. In addition to decreasing TWDP, data dependent jitter is also reduced for data transmission across a channel that exhibits a multi-pole transmission characteristic. A main data signal and at least one cursor signal, which is shifted at least a portion of a clock period from the main data signal, is generated. The cursor signal is filtered to filter out effects based on the second pole of the multi-pole transmission characteristic. The main data signal is subtracted from the filtered cursor signal to generate the transmitter output data signal.

Abstract: A dispersion determining apparatus comprises a received waveform monitoring part (1) and a dispersion amount determining part (4). The received waveform monitoring part (1) has a waveform monitoring circuit (2) that samples data from the received waveform of a received signal having propagated along a transmission path, and a histogram extracting circuit (3) that extracts, based on the sampled data obtained by the waveform monitoring circuit (2), a histogram data representative of the intensity distribution in the voltage direction of the received waveform. The dispersion amount determining part (4) has a polarized wave dispersion estimating circuit (7) that determines the horizontally asymmetric degree of a received eye-pattern waveform of the received waveform obtained by analyzing the histogram data extracted by the received waveform monitoring part (1) and then estimates, based on the determined asymmetric degree, a polarized wave dispersion amount in the transmission path.

Abstract: An optical transmitter includes: a pre-compensator calculating an electrical field of an optical signal subjected to an electronic pre-compensation with respect to an input digital signal; a parallelizer parallelizing the electrical field of the optical signal calculated by the pre-compensator; a plurality of optical modulators modulating an optical signal based on each of parallelized electrical fields of optical signals; and a time-division multiplexer time-division-multiplexing an optical signal output from the plurality of the optical modulators.

Abstract: A data transport card comprising an interface to receive high speed data streams from at least one client, and a pluggable conversion module which converts said data streams into optical data signals and couples these optical data signals into at least one wavelength division multiplexing channel for transport of said optical data signals via an optical fiber.

Abstract: An optical signal of an optical transmission part is brought into a high-speed polarization scrambling state by a polarization scrambling part, and transmitted to en optical fiber transmission line as the optical signal from the optical transmitter. The optical signal passing through the optical fiber transmission line is inputted to an optical receiver. The optical signal inputted to the optical receiver is converted into an electric signal by a polarization dependent photoelectric detection part. The converted electric signal is inputted to a digital signal processing part having a polarization scrambling cancel part of canceling the polarization scrambling state by a digital signal processing operation. At the digital signal processing part, the polarization scrambling state of the electric signal is canceled, and a data signal is outputted.

Abstract: An optical receiver includes a two-stage constant modulus algorithm (CMA) equalizer. The first stage is a modified version of a CMA equalizer and the second stage is a conventional CMA equalizer. The first stage may be made up of four sub-equalizers, of which only two of the sub-equalizers are independent, i.e., uncorrelated to each other. This first stage equalizer compensates for polarization-mode dispersion (PMD). The second stage equalizer is a conventional CMA equalizer made up of four sub-equalizers that are adjusted independently. This second stage equalizer may compensate for polarization-dependent loss (PDL). The receiver includes a first processor that determines PMD information based on a plurality of transfer function parameters of the modified CMA equalization of the first stage equalizer and the modified-equalized output and a second processor that determines PDL based on a plurality of transfer function parameters of the CMA equalization of the second stage equalizer.

Abstract: Provided is an apparatus and method for transmitting and receiving data in a visible light communication system, the apparatus including a visible light communication (VLC) transceiver for converting a visible light signal received from a counterpart into an electrical signal and outputting the electrical signal, by using a light receiving device during a reception operation, and converting an electrical signal containing information into a visible light signal and transmitting the visible light signal to the counterpart, by using a light emitting device during a transmission operation, a VLC controller comprising a visible frame engine (VFE) for generating a visible frame and outputting the visible frame to the VLC transceiver, in which the VFE generates the visible frame for transmission to a counterpart during non-transmission of respective frames for communication at a sender and a receiver in order to provide visibility to a communication link, and a host controller for controlling the VLC controller and

Abstract: Systems and methods are disclosed for compensating for impairments caused by a semiconductor optical amplifier (SOA). One such method comprises receiving an optical signal which has been distorted in the physical domain by an SOA, and propagating the distorted optical signal backward in the electronic domain in a corresponding virtual SOA.

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: A distortion compensating apparatus which compensates for distortion in a waveform of a received light signal through a digital signal processing includes a plurality of fixed amount compensators which compensate for the distortion in the waveform at respective given compensating amounts. The combination of operating states of the plurality of fixed amount compensators is changed by on/off switching of each of the plurality of fixed amount compensators, and the plurality of fixed amount compensators are cascaded.

Abstract: Systems and method of compensating for transmission impairment are disclosed. One such method comprises receiving a wavelength-division multiplexed optical signal. The received optical signal has been distorted in the physical domain by an optical transmission channel. The method further comprises propagating the distorted optical signal backward in the electronic domain in a corresponding virtual optical transmission channel. The backward propagation fully compensates for fiber dispersion, self-phase modulation, and cross-phase modulation (XPM) and partially compensates for four-wave mixing (FWM).

Abstract: A polarization mode dispersion compensator that includes two stages, one for reducing or eliminating first order polarization mode dispersion of an optical signal, and second stage for reducing or eliminating higher order polarization mode dispersion of the optical signal. In each stage, the polarization is adjusted so as to reduce polarization mode dispersion. Based on the power levels of various polarization states generated at the second polarization controller, the optical signal to noise ratio may be estimated. Furthermore, based on the amount of adjustment used to control the polarization controllers and the differential group delay, the polarization mode dispersion may be estimated.

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: Systems and methods of compensating for transmission impairment are disclosed. One such method includes receiving a polarization-division multiplexed optical signal which has been distorted in the physical domain by an optical transmission channel, and propagating the distorted polarization-division multiplexed optical signal backward in the electronic domain in a corresponding virtual optical transmission channel.

Abstract: A method and apparatus are provided for attenuating an optical beam. The method includes selecting a level of attenuation to be applied to the optical beam. A pattern of on-state and off-state pixels in a two dimensional spatial light modulator (SLM) is selected such that the pattern will modulate the optical beam to provide the selected level of attenuation. Finally, the optical beam is directed onto the SLM while tile pixels are arranged in the selected pattern. The pattern is periodic along a first axis and symmetric along a second axis along which an intensity distribution of die optical beam extends.

Abstract: Disclosed is a visible light communication system including a transmission device, including multiple light emitting units emitting light of different colors and mapping transmission data to a chromaticity point, calculating luminescence of each of the light emitting units, generating a preamble signal for channel matrix estimation, and emitting light based on the preamble signal and calculated luminescence amount. A reception device of the visible light communication system includes multiple light receiving units and estimates a channel matrix based on a corresponding optical signal when an optical signal corresponding to the preamble signal is received in each light receiving unit, compensates the optical signal corresponding to the chromaticity point for a propagation path based on the estimated channel matrix, detects a chromaticity point on the chromaticity coordinates based on a signal after the propagation path compensation, and demodulates the transmission data.

Abstract: A waveform shaping apparatus includes a quantum dot optical amplifier in which an amplification factor of input signal beams saturates if the optical power of the signal beams is equal to or greater than a predetermined value; and a quantum dot saturable absorber in which an absorption factor of the input signal beams saturates if the optical power of the signal beams is under a predetermined value. The quantum dot optical amplifier and the quantum dot saturable absorber are connected in series with a transmission path of the signal beams, and shape the waveform of the signal beams. Voltages applied to the quantum dot optical amplifier and the quantum dot saturable absorber, respectively, are adjusted based on the optical power of the signal beams.

Abstract: An optical transmission system is provided with an optical transmission apparatus, an optical reception apparatus, an optical transmission line redundantly configured with an active system optical transmission line and an standby system optical transmission line, an optical switch that switches an optical transmission line between the active system optical transmission line and the standby system optical transmission line, a variable dispersion compensator placed between the optical switch and the optical reception apparatus, a dispersion amount measuring unit that measures the dispersion amount of the standby system optical transmission line when the active system optical transmission line is being selected by the optical switch, a dispersion compensation amount setting unit that sets the amount of dispersion compensation to be applied to the standby system optical transmission line based on the measured dispersion amount of the standby system optical transmission line, and a control unit that controls, when

Abstract: A system and method for in-service optical dispersion determination are provided. Optical dispersion is determined by splitting a first optical signal into two components, introducing a time delay between the two components such that corresponding pulses of the two components partially overlap, combining the two components to generate a combined optical signal comprising a first component and a second component, determining power of the combined optical signal while applying a plurality of dispersion compensation values, in order to determine a dispersion compensation value that results in a minimum detected power of the combined optical signal. Polarization Mode Dispersion is determined by adjusting the time delay that is introduced until the power of the combined optical signal is substantially equal for all of the plurality of dispersion compensation values.

Abstract: A propagation apparatus includes a plurality of dispersion compensation execution units which accept a signal of a single wavelength from a wavelength-multiplexed signal which is received and execute dispersion compensation on the signal by inputting the accepted signal to a tunable dispersion compensator with an adjusted dispersion value, and a dispersion value calculation unit which acquires each dispersion value adjusted by the plurality of the dispersion compensation execution units, approximates the dispersion value of the wavelength assigned to a newly built line by using the acquired dispersion values whose signal error rates are in a tolerable range, and sets the approximated dispersion value as an initial value in the tunable dispersion compensator of the newly built line.

Abstract: A system and method are provided for controlling the pre-emphasis applied to an optical signal, in which the output level of individual transmitters is controlled in order to reach a pre-defined desired value of a quality metric. Transmitters are able to adjust their output power without external control in such a way as to optimise the power distribution across the system.

Abstract: An optical receiver for receiving an optical signal that transmits a first data signal and a second data signal, including: an optical front-end configured to generate a digital signal that represents the optical signal; a detector configured to detect a state of the optical signal by using the digital signal and output state information that represents the state of the optical signal; a state controller configured to control the digital signal on the basis of the state information in order to recover the first data signal; and a data recovery configured to recover the second data signal on the basis of the state information.

Abstract: An apparatus comprises an optical transmitter that comprises a processor and at least one optical modulator. The processor is configured to generate electronic representations of at least two pre-dispersion-compensated phase-conjugated optical variants carrying a same modulated payload data for transmission. The at least one optical modulator is configured to modulate the electronic representations, wherein an amount of dispersion induced on the pre-dispersion-compensated phase-conjugated optical variants depends on an accumulated dispersion (AD) of a transmission link through which the pre-dispersion-compensated phase-conjugated optical variants are to be transmitted. The amount of dispersion induced on the phase-conjugated optical variants may be approximately ?AD/2, where AD is the accumulated dispersion of the transmission link.

Abstract: A detection system and method may be used to detect data transmitted in a signal with data pattern dependent signal distortion such as intersymbol interference. In general, a detection system and method compares samples of a received signal with stored samples of distorted signals associated with known data patterns and selects the known data patterns that correspond most closely with the samples of the received signal. The detection system and method may thus mitigate the effects of data pattern dependent signal distortion.

Abstract: A method for compensating for optical dispersion includes receiving an optical signal at a first node of an optical network that includes a first set of channels and a second set of channels that are each configured to be received using coherent digital receivers at a second node of the optical network. Each coherent digital receiver provides electronic dispersion compensation for the received channel at the second node. The method also includes forwarding the first set of channels from the first node without performing optical dispersion compensation on those channels. Furthermore, the method includes compensating for optical dispersion in the second set of channels at the first optical node and forwarding those channels from the first node. The optical dispersion compensation on the second set of channels at the first node provides dispersion compensation in addition to the compensation provided by the associated coherent digital receivers at the second node.

Abstract: To reduce emission of an unintentional electromagnetic wave even if a frequency of a clock signal being output is high, a printed circuit board (10) includes: a substrate (101); signal output circuits (102 and 103) formed on the substrate (101), for outputting a clock signal; power supply wirings (109 and 110) for connecting the signal output circuits (102 and 103) and a power source; and trap filters (107 and 108) provided to the power supply wirings (109 and 110), for attenuating a frequency component corresponding to a frequency of the clock signal.

Abstract: The chromatic dispersion of an optical component is measured with high accuracy using a simple set-up, which includes a pump light source, a probe light source, and a measuring means. Pump light having a wavelength ?pump and probe light having a wavelength ?probe is propagated through an optical component, with the wavelength ?probe being apart from the wavelength ?pump by a given frequency. The generation efficiency of the idler light with respect to the wavelength ?pump is calculated by measuring the power of idler light having a wavelength ?idler output from the optical component, and by seeking the pump light wavelength for making the generation efficiency a local extreme value, the chromatic dispersion of the optical component is calculated from the result of calculation of phase mismatch among the pump light wavelength having such wavelength as sought, the corresponding probe light wavelength, and the corresponding the idler light wavelength.

Abstract: An optical transmission system is provided. The optical transmission system includes a user side optical repeater device, a central office side optical repeater device, and wavelength multiplexing and wavelength de-multiplexing functions. The user side optical repeater device is to be connected with a user side optical network unit, transmits data in two ways, and is used for wavelength division multiplexing. The central office side optical repeater device is to be connected with a central office side optical line terminal, transmits data in two ways, and is used for wavelength division multiplexing. The wavelength multiplexing and wavelength de-multiplexing functions are used for relaying between the user side optical repeater device and the central office side optical repeater device.

Abstract: Methods of transmitting an optical signal through optical fiber in a manner suppressing stimulated Brillouin scattering (SBS) are provided. A light beam emitted from a light source is modulated by driving either the light source or a separate phase modulator or both simultaneously with a separate high frequency signal dithered by one or more low frequency dithering signals of a frequency or frequencies lower than that of the high frequency signal. Thereafter, the light beam is further modulated externally with an RF information-carrying signal. The high frequency signal is at least twice a highest frequency of the RF information-carrying signal. The light beam modulated with the RF information-carrying signal is coupled into optical fiber.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

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: An OADM in a wavelength division multiplexing transmission system includes a wavelength selection switch that selects a predetermined wavelength from a multiple optical signal obtained by multiplexing a phase modulated signal and an intensity modulated signal and outputs the selected wavelength signal to a predetermined output port. The wavelength selection switch has a different delay for each wavelength of the multiple optical signal. For example, the wavelength selection switch includes a mirror array. Optical paths from the surfaces of mirrors arranged on the mirror array to the diffraction grating are different in the case of adjacent mirrors.

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.

Abstract: A dispersion compensation device includes: an optical branching unit to branch an optical signal to be received; a first dispersion compensator to perform dispersion compensation on one part of the optical signal branched by the optical branching unit with a variable compensation amount; a second dispersion compensator to perform dispersion compensation on another part of the optical signal branched by the optical branching unit; a monitoring unit to monitor the communication quality of an output optical signal of the second dispersion compensator; and a controlling unit to determine the direction of variation in chromatic dispersion of the optical signal based on the direction of variation in communication quality monitored by the monitoring unit and control the compensation amount of the first dispersion compensator based on the result of the determination.

Abstract: An optical demultiplexer (13, 30) for wavelength division multiplex WDM optical radiation comprising a plurality of wavelength channels (Ch1 . . . Ch16) spaced over a wavelength spectrum said demultiplexer being for separating the WDM radiation into individual wavelength channels is described. The demultiplexer comprises a first demultiplexer (12) for dividing the W-DM radiation into a plurality of sub-bands (Ch1 . . . Ch4, Ch5 . . . Ch8, Ch9 . . . Ch12, Ch13 . . .

Abstract: A receiver includes wavelength demultiplexer for demultiplexing a received WDM light into light signals at respective central frequencies thereof, delay interferometer for converting a light signal output from wavelength demultiplexer into an intensity signal, and light detector for converting an output signal from delay interferometer into an electric signal. The interval between interferential frequencies of delay interferometer is 2/(2n+1) times the interval between the central frequencies of the WDM light. Logic inverting circuit outputs the output signal from the light detector while non-inverting or inverting the logic level thereof depending on the received central frequency.

Abstract: Various example embodiments are disclosed. According to one example embodiment, a phase error is estimated in a series of digital symbols of a phase-modulated signal, where the signal is subject to a non-linear phase shift error due to transmission of the signal through an optical fiber. A phase correction of an instant digital symbol that succeeds the series of digital symbols is estimated, where the estimated phase correction is based on the estimated phase errors in the series of digital symbols. The estimated phase correction of the instant digital symbol is limited to a maximum absolute value, and the estimated phase correction is applied to the instant digital symbol of the signal.