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 apparatus comprises a coherent optical transmitter. The coherent optical transmitter comprises a first modulator for generating a first polarization, a second modulator for generating a second polarization, and a symbol interleaver configured to receive a first symbol stream intended to be transmitted on a first polarization and a second symbol stream intended to be transmitted on a second polarization, to direct one portion of symbols of the first symbol stream to the first modulator for modulation onto the first polarization and another portion of the symbols of the first symbol stream to the second modulator for modulation onto the second polarization, and to direct one portion of symbols of the second symbol stream to the first modulator for modulation onto the first polarization and another portion of the symbols of the second symbol stream to the second modulator for modulation onto the second polarization.

Abstract: When designing a demodulator for a DPSK-modulated signal, it is required that optical phase modulation is performed fast and the demodulator has a long lifetime. To achieve this object, a delay line interferometer inside the demodulator performs adjustment of phase difference between two split lights caused to interfere, using a first optical phase modulation unit such as a Piezo actuator and a second optical phase modulation unit such as a heating element that operates slower in modulation speed than the first optical phase modulation unit and is slower in deterioration speed.

Abstract: A loop filter include: a register that stores a result of arithmetic operation performed on a complex signal and outputs the stored complex signal; a first multiplier that multiplies the complex signal output from the register and a predetermined coefficient; an absolute value judging unit that outputs a multiplier coefficient used to control such that the amplitude of the complex signal output from the register is held in a predetermined range; a multiplier that multiplies an output from the first multiplier and the multiplier coefficient; a second multiplier that multiplies an input signal and a value (1?the predetermined coefficient); and an adder that adds an output from the multiplier to an output from the second multiplier and inputs a result of addition into the register.

Abstract: The present disclosure relates to the field of communications, and in particular, to a coherent receiver apparatus and a chromatic dispersion compensation method. The apparatus includes a polarization beam splitter and a chromatic dispersion compensation module. An optical splitter is disposed in front of the polarization beam splitter, and a chromatic dispersion monitoring module is connected between the optical splitter and the chromatic dispersion compensation module. The optical splitter is configured to split a modulated optical signal received by the coherent receiver apparatus and then transmit the split modulated optical signal to the chromatic dispersion monitoring module and the polarization beam splitter.

Abstract: The present invention discloses a receiving apparatus, a sending apparatus, a system and a method for optical polarization division multiplexing.

Abstract: In a free space optical system type demodulator of a phase shift keying signal, if a half beam splitter is used as a non-polarizing optical branching unit that is used when generating beams corresponding to I and Q channels or when multiplexing an interference light, control of a power branching ratio is difficult, and it is necessary to suppress phase shifts that are different depending on a polarization state of an input state, and thereby the demodulator becomes high cost. Moreover, since directions of branched lights are different, it is difficult to suppress a skew of the demodulator. In the present invention, the non-polarizing optical branching unit that is used when generating the beams corresponding to the I and Q channels and when multiplexing the interference light is realized using polarization rotating elements and polarization separating elements. Moreover, branched beams are substantially aligned.

Abstract: A system receives traffic that includes four-bit symbols, the four-bit symbols being encoded using a four-bit phase modulation scheme; and processes the traffic to recover a four-bit symbol. The system also decodes the recovered four-bit symbol to obtain a three-bit symbol. The three-bit symbol is associated with a three-quadrature amplitude modulation (3QAM) scheme, and the decoding is performed without creating an error, within the traffic, when cycle slip occurs. The system outputs the traffic based on the three-bit symbol.

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: In a coherent optical receiver of an optical communications system, methods and systems for receiving a data signal x(t) modulated on an optical signal. A linearly polarized LO light is generated, which has a frequency of f1=f0±?f, where f0 is a frequency of a narrowband carrier of the optical signal, and ?f corresponds with a band-width fB of the data signal x(t). The LO light and a received light of the optical signal are heterodyned on a photodetector. An analog signal generated by the photodetector is low-pass filtered to generate a filtered signal, using a filter characteristic having a sharp cut-off at a frequency of ?f+nfB, where n is an integer multiple. An analog-to digital (A/D) converter samples the filtered signal at a sample rate of 2(?f+nfB) to generate a corresponding multi-bit digital sample stream. The multi-bit digital sample stream is digitally processed to recover respective In-Phase and Quadrature components of the received light of the optical signal.

Abstract: There is a need to prevent two receivers from converging on a state of receiving the same polarization state, fast start receivers, and ensure highly reliable operations. A polarization-multiplexed transmitter previously applies frequency shifts of frequencies +?f and ??f to X-polarization and Y-polarization digital information signals to be transmitted. Optical field modulators modulate and polarization-multiplex the signals. As a result, a frequency difference of 2?f is supplied to X-polarization and Y-polarization components. A polarization diversity coherent optical receiver 215 receives the signal. A frequency estimation portion in a digital signal processing circuit detects a frequency difference signal in both polarization components. This signal is used to a polarization splitting circuit in the digital signal processing circuit.

Abstract: A method is provided for performing chromatic dispersion (CD) compensation. A zero-forcing filter is calculated with a number of taps (n) required to nullify a chromatic dispersion frequency response of an optical channel. The number of taps in the zero-forcing filter is truncated to a number equal to (n?x), where x is an integer greater than 0. In one aspect, the chromatic dispersion frequency response of the optical channel is partitioned into a plurality of constituent chromatic dispersion responses, and a zero-forcing filter is calculated for each of the plurality of constituent chromatic dispersion responses. The number of taps in each of the plurality of zero-forcing filters is truncated, and the CD compensation filter is formed for each of the plurality of truncated tap zero-forcing filters. In another aspect, the tap values of the zero-forcing filter are quantized to a finite quantization set.

Abstract: In order to compensate for chromatic dispersion caused by optical fiber transmission in a communication system with coherent detection using optical signals, specific frequency band signals are used to enable estimation of a chromatic dispersion value.

Abstract: Embodiments of the present disclosure relate to a signal transmission method The signal receiving method includes: receiving a first transmit signal, where the first transmit signal includes a first polarized optical signal and a second polarized optical signal that are perpendicular to each other, where the first polarized optical signal is loaded with first data, the first transmit signal is an uplink signal, and the first data is uplink data, or, the first transmit signal is a downlink signal, and the first data is downlink data; splitting the first transmit signal into a first signal and a second signal according to power; separately rotating a first polarized optical signal and a second polarized optical signal of the second signal by 90 degrees; and performing coherent mixing on the rotated second signal and the first signal to obtain the first data.

Abstract: The first photon in single-photon state is divided into two components by the half beam splitter, and the first component is sent to the sender while the second component is sent to the receiver. The sender measures the first component of the first photon when he sends “1”. The sender doesn't measure the first component of the first photon when he sends “0”. The receiver makes the second component of the first photon enter into the Sagnac interferometer, and the receiver also makes the reference light enter into the Sagnac interferometer at the same time. The receiver makes the second component of the first photon interact with the reference light in the nonlinear optical medium arranged in the Sagnac interferometer. The receiver knows the signal from the phase modulation of the reference light caused by the interaction with the second component of the first photon.

Abstract: In order to reduce influence of noise due to a phase deviation, and to estimate an amount of phase compensation with superior accuracy in a polarization multiplexing/demultiplexing optical communication system, a signal processing circuit includes: optical frequency deviation estimating unit for estimating a frequency deviation which is a difference between a frequency of local light and a frequency of the optical carrier wave which is included in a signal data which corresponds to the polarizations and are generated by mixing a plurality of the optical carrier waves with the local light, which optical carrier wave is phase-modulated and have polarizations able to be demultiplexed and for outputting the estimated frequency deviation as an estimated value; for outputting the estimated frequency deviation as an estimated value; optical frequency deviation compensation amount analyzing unit for calculating an amount of frequency compensation which is an amount of compensation to make a phase of the signal data r

Abstract: Systems and methods are disclosed to provide optical communication by using subcarriers as individual bases functions, obtaining signal constellation points of an N-dimensional pulse amplitude modulation (ND-PAM) constellation diagram as an N-dimensional Cartesian product of a one-dimensional PAM; and transmitting the N-dimensional signal constellation point over all N orthogonal subcarriers serving as individual bases functions.

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: An optical receiving apparatus includes a combining unit that combines signal light and reference light; a optoelectric converting unit that converts, into electrical signals, two or more optical signals that enable reconstruction of a complex electric field signal of the signal light obtained by the combining unit; and a sampling clock generating unit that generates a sampling clock that has a frequency preset based on a symbol rate of the signal light and is asynchronous with the signal light. The optical receiving apparatus further includes a digital converting unit that samples at the frequency of the sampling clock signal, an electrical signal obtained by the optoelectric converting unit and converts the electrical signal into a digital signal; and a digital signal processing unit that demodulates a received signal based on a complex digital signal obtained from the digital signal obtained by the digital converting unit.

Abstract: An optical communication system includes a polarization multiplexed orthogonal frequency-division multiplexing POLMUX-OFDM transmitter for generating a POLMUX-OFDM double sideband signal, an optical processing path for processing the double sideband signal from the transmitter; an analog-to-digital convert ADC-OFDM receiver coupled to the optical processing path for receiving the double sideband signal processed by the optical path; and a block-diagonal multiple-input multiple-output MIMO equalizer responsive to the receiver for enabling correct operation for a completely random incoming signal polarization state without adaptive polarization control at said receiver, which enables complexity.

Abstract: A method includes producing interference between a received optical OFDM signal and an optical carrier extracted from the received optical OFDM signal to provide optical coherent detection of the received optical OFDM signal. Preferably, producing the interference includes optically splitting the received optical OFDM signal into a first part that is filtered to extract the carrier from the received optical OFDM signal and a second part similar to the received optical OFDM signal.

Abstract: In order to reduce influence of noise due to a phase deviation, and to estimate an amount of phase compensation with superior accuracy in a polarization multiplexing/demultiplexing optical communication system, a signal processing circuit includes: optical frequency deviation estimating unit for estimating a frequency deviation which is a difference between a frequency of local light and a frequency of the optical carrier wave which is included in a signal data which corresponds to the polarizations and are generated by mixing a plurality of the optical carrier waves with the local light, which optical carrier wave is phase-modulated and have polarizations able to be demultiplexed and for outputting the estimated frequency deviation as an estimated value; for outputting the estimated frequency deviation as an estimated value; optical frequency deviation compensation amount analyzing unit for calculating an amount of frequency compensation which is an amount of compensation to make a phase of the signal data r

Abstract: Methods, systems, and devices are described for tap adjustment and reseeding in a digital filter. Filter and signal characteristics are measured and tap adjustments and reseeding of tap values may be performed based on the filter and signal characteristics. Filter characteristics that may be measured include a filter center of mass which may provide an indication that filter taps for a filter may be drifting toward a filter edge and thus reducing the dynamic range of the filter. Signal characteristics may include a timing offset between received input signals, and characteristics related to which of a particular input signal is present at a filter output. Filter taps, according to various embodiments, may be adjusted, and/or re-initialized responsive to one or more of the signal or filter characteristics.

Abstract: A method for data processing in an optical network includes providing at least one main wavelength and processing a subcarrier modulation for the at least one main wavelength, wherein a portion of the subcarrier modulated signal is suppressed. An optical network component and a communication system having such an optical network component are also provided.

Abstract: The present disclosure provides a polarization multiplexed transceiver, including: a transmitter; a receiver; circuitry within the transmitter configured to insert pilot tones as a reference state of polarization for a polarization multiplexed signal; and circuitry within the receiver configured to de-multiplex the polarization multiplexed signal using the pilot tones. The transmitted signal is constructed in such a manner as to facilitate the division of the receiver processing between the analog and digital domains such that the implementation may be simultaneously both highly spectrally efficient and power efficient.

Abstract: A heterodyne optical signal detector and method performed thereby, the signal detector including an optical signal spectrum shaper operable to modify the shape of the frequency spectrum of a received optical signal, a laser local oscillator (LO), and polarization beam splitters (PBSs) to divide the signal and the LO into orthogonal components, waveguides in which intermediate frequency (IF) signals are formed, balanced photodetectors (BPDs) arranged to receive the IF signals and operable to convert the IF signals into electric signals, and analog to digital converters (ADCs) that digitize the electric signals.

Abstract: An optoelectronic transmission system has a photoemitter semiconductor component and a photodetector semiconductor component. The photoemitter semiconductor component has a radiation source for converting a first electrical signal into a first electromagnetic radiation and a first polarization filter having a first polarization direction for filtering the first electromagnetic radiation. The photodetector semiconductor component has a second polarization filter having a second polarization direction for filtering a second electromagnetic radiation and a sensor element for converting a second electromagnetic radiation which has been polarized by the polarization filter into a second electrical signal. In this case, the first polarization direction of the first polarization filter is identical to the second polarization direction of the second polarization filter.

Abstract: An optical heterodyne device includes an optical meta-material exhibiting non-linear behavior. The optical meta-material mixes an input signal and a local signal to produce a heterodyne signal.

Abstract: An adaptive equalizer includes a finite impulse response filter with a predetermined number of taps; and a tap coefficient adaptive controller having a register to hold tap coefficients for the filter, a weighted center calculator to calculate a weighted center of the tap coefficients, and a tap coefficient shifter to shift the tap coefficients based on a calculation result of the weighted center. During an initial training period, the tap coefficient shifter shifts the tap coefficients on a symbol data basis such that a difference between the calculated weighted center of the tap coefficients and a tap center defined by the number of taps is minimized.

Abstract: An optical modulation apparatus includes a first modulator, a second modulator, a multiplexer, a calculator and an adjustor. The first modulator configured to modulate light emitted by a light source using a first input signal and output a first modulated signal. The second modulator configured to modulate the light using a second input signal and output a second modulated signal. The multiplexer configured to multiplex the first and second modulated signals and output a multiplexed signal. The calculator configured to calculate a power difference between a higher-side frequency component having a frequency higher than a center frequency of the multiplexed signal and a lower-side frequency component having a frequency lower than the center frequency. The adjustor configured to adjust delays of the first and second input signals based on the power.

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 being encoded through a pulse position modulation (PPM) format and some being encoded through an additional modulation format on at least one PPM pulse. A receiver detects the signal through a dual-polarization coherent receiver front-end, recovering 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: 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: A digital coherent receiver converts signals and local light respectively detected, as detection results, in signal light from an optical transmission line, into digital signals and that further applies digital processing to the digital signals. The receiver includes a skew detecting unit that detects skew between the digital signals; a skew control unit controls the skew of each of the signals so that the skew to be detected by the skew detecting unit will be reduced; and a demodulating unit that demodulates each signal controlled for skew by the skew control unit.

Abstract: A polarization diversity optical system device includes: a polarization split unit that splits a first coherent light into a first split light and a second split light whose polarization components are orthogonal to each other, and splits a second coherent light into a third split light and a fourth split light whose polarization components are orthogonal to each other; and a light combining unit that combines the first split light with one of the third split light and the fourth split light, and combines the second split light with the other of the third split light and the fourth split light.

Abstract: A method and system for mitigating distortion in coherent single-ended photo-detection is disclosed. The methodology comprises: receiving an optical signal carried on an optical transmission medium and coherently detecting the received optical signal to produce a digitized signal; estimating a time-dependent random variable introducing distortion to the coherently detected signal; and subtracting the distortion from digitized signal to produce a distortion mitigated output signal.

Abstract: A method, apparatus and system for providing clock and data recovery in a receiver for receiving a high speed coherent polarization division multiplexed optical signal using a digital signal processing block including a spectral domain spatial combiner are provided.

Abstract: A digital coherent receiving apparatus includes a first oscillator for outputting a local light signal of a fixed frequency, a hybrid unit mixing the local light signal with a light signal received by a receiver, a second oscillator for outputting a sampling signal of a sampling frequency, a converter for converting the mixed light signal into digital signal synchronizing with the sampling signal, a waveform adjuster for adjusting a waveform distortion of the converted digital signal, a phase adjustor for adjusting a phase of the digital signal adjusted by the waveform adjustor, a demodulator for demodulating the digital signal adjusted by the phase adjuster, and a phase detector for detecting a phase of the digital signal adjusted by the phase adjuster, and a control signal output unit for outputting a frequency control signal on the basis of the detected phase signal to the second oscillator.

Abstract: A system configured to maintain a consistent local-oscillator-power-to-primary-signal-power ratio (LO/SIG ratio).

Abstract: Digital timing error detection systems and techniques are described. The described techniques are independent of polarization and differential-group-delay and are used to perform timing recovery of polarization-multiplexed coherent optical systems.

Abstract: A system configured to maintain a consistent local-oscillator-power-to-primary-signal-power ratio (LO/SIG ratio).

Abstract: A optical detection apparatus includes: an optical splitting unit configured to split a seed lightwave and split upward signal light generated by an optical network unit, based on the seed lightwave; a first control unit configured to control polarizations of the split seed lightwaves based on a first electrical signal; a second control unit configured to control phases of the split seed lightwaves based on a second electrical signal; an optical coupling and signal conversion unit configured to couple the seed lightwaves, of which the polarization and phase are controlled, and the split upward signal lights, convert the coupled optical signals into the first and second electrical signals, and transfer the first and second electrical signals to the first and second control units, respectively; and a signal detection unit.

Abstract: From an real valued OFDM signal (S0(t)) is a baseband signal (SB(t)) derived and converted into a complex single sideband modulation signal (n(t)). This is modulated onto an optical carrier (fOC) to generate a SSB transmission signal (SOT) having a small bandwidth an carrying the information in the envelope or in the power of the envelope. According to the modulation direct detection is possible. Only a small bandwidth is necessary for the transmission.

Abstract: An apparatus for receiving optical signals in DQPSK and method of controlling a phase offset in receiving optical signals for DQPSK is provided. An original optical signal modulated in DQPSK is received. The original optical signal is delayed by one bit to make a delay optical signal such that an interference on the original optical signal and the delay optical signal is performed. A control signal is generated by use of an interference result between the original optical signal and the delay optical signal. A phase offset for the interference between the original optical signal and the delay optical signal is controlled by use of the generated control signal. In receiving optical signals, the phase offset between the delay optical signal and the original optical signal is precisely controlled, thereby optimizing the transfer characteristics of an optical delay interferometer.

Abstract: A method for detecting and measuring time skew in high-speed DP-QPSK coherent optical receivers is described.

Abstract: An apparatus comprising an optical receiver configured to receive an optical signal, and a combined level and clock recovery circuit coupled to the optical receiver and configured to update a signal threshold and a clock phase substantially simultaneously. Also included is an apparatus comprising at least one processor configured to implement a method comprising recognizing reception of a signal, and adjusting a threshold and a clock phase associated with the signal using a rising time for the signal and a falling time for the signal. Also included is a method comprising receiving a signal, and adjusting a threshold level of the signal to establish level recovery using a clock recovery scheme.

Abstract: In a polarization-multiplexing optical communications system, a method and system for coherent reception of polarization-multiplexed optical communications. Training and data sequences are recovered from a plurality of orthogonally polarized signals, such that training and data sequences may be used on a single channel without loss of spectral efficiency. This is accomplished by estimating a channel response for each orthogonally polarized signal based on the mean of the signal and distinguishing between a data sequence and a training sequence in each orthogonally polarized signal. Such distinguishing is accomplished according to an iterative linear minimum mean-square equalization based on the respective channel response estimate.

Abstract: An apparatus for receiving optical signals in DQPSK and method of controlling a phase offset in receiving optical signals for DQPSK is provided. An original optical signal modulated in DQPSK is received. The original optical signal is delayed by one bit to make a delay optical signal such that an interference on the original optical signal and the delay optical signal is performed. A control signal is generated by use of an interference result between the original optical signal and the delay optical signal. A phase offset for the interference between the original optical signal and the delay optical signal is controlled by use of the generated control signal. In receiving optical signals, the phase offset between the delay optical signal and the original optical signal is precisely controlled, thereby optimizing the transfer characteristics of an optical delay interferometer.

Abstract: In present invention, a filter coefficient adjustment apparatus is used in a polarization demultiplexer which demultiplexes the input signals by using filters to obtain demultiplexed output signals, said filter coefficient adjustment apparatus being used for adjusting the coefficients of the filters, wherein said filter coefficient adjustment apparatus comprises: an logarithm partial derivative calculation unit for calculating the logarithm partial derivative value of a target probability density function of the demultiplexed output signals when its self-variable value is the present demultiplexed output signal value; a gradient calculation unit for calculating the gradient of a target optimizing function for optimizing the distribution of the multiplexed output signals based on the logarithm partial derivative value calculated by the logarithm partial derivative calculation unit; and a filter coefficient updating unit for updating the coefficients of the filters based on the gradient calculated by the gradie

Abstract: An adaptive-equalizer initialization system performs three functions: frequency offset estimation, taps estimation for chromatic dispersion filters, and taps initialization for an adaptive equalizer. The system contains hardware FFT and peak detector units that sense a pure tone that marks the beginning of a known, short data sequence.

Abstract: An optical receiver includes a photo-detector that converts a received optical signal into an electric signal and outputs the electric signal, a converter that converts the electric signal into a parallel data signal and outputs the parallel data signal, and parallel-number changer changing a parallel number of the parallel data signal in accordance with a bit rate of the optical signal and outputting the parallel data signal having the changed parallel number.