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: Optical communications networks rely on optical receivers to demodulate optical signals and convert the demodulated optical signal into an electrical signal. Optical receivers may be associated with one or more characteristics which can be made to vary during a transmission of an optical signal in order to improve the quality of the received signal. The present invention may determine a value for the characteristics based on an amount of optical filtering on a communications link which transmits the signal. The value for the characteristics of the receiver may be determined by observing a characteristic of a detector associated with the receiver, such as a ratio of the average photocurrents of the constructive and destructive ports of the detector. The observed characteristic of the detector may be mapped to a predetermined value for the characteristic of the receiver in a lookup table, which may be queried during operation of the receiver.

Abstract: This invention relates to a phase control circuit for an optical receiver (1). The phase control circuit (9, 19) comprises a non-linear element (22) and a power detector (24). The non-linear element (22) has a rectifying characteristic, inputs the received electrical signal (7, 17) and provides a rectified signal at its output. The power detector (24) provides an error signal which is used to obtain a phase control signal (5) which is output by the phase control circuit. The invention further relates to a corresponding method for phase control of an optical receiver (1).

Abstract: Provided is an optical multilevel transmission system, comprising at least one optical multilevel transmitter for transmitting an optical multilevel signal obtained and an optical multilevel receiver for receiving the optical multilevel signal. The received optical multilevel signal has a larger noise in an angular direction than in a radial direction. The optical multilevel receiver sets, in a symbol decision of the received optical multilevel signal demodulated on the complex plane, for positions of all or some of ideal signal points, a width in the angular direction of a decision area, to which each of the ideal signal points belongs and which is measured along a circumference of a circle centered at an origin and passing through a center of the each of the ideal signal points, larger than a width in the angular direction of a decision area defined based on a Euclidean distance.

Abstract: Methods, systems, and devices are described for compensating for a coarse frequency offset between a received optical signal and a local oscillator at a demodulator. Multiple samples are received of an output of a discrete Fourier transform performed on the received optical signal. A magnitude of each sample is determined, and the determined magnitudes may be filtered by a digital domain filter. A difference is computed between the determined magnitudes for a first set of the samples and the determined magnitudes for a second set of the samples, and a local oscillator correction factor is generated based on at least the computed difference.

Abstract: In a coherent optical receiver, sufficient demodulation becomes impossible and consequently receiving performance deteriorates if an inter-channel skew arises, therefore, a coherent optical receiver according to an exemplary aspect of the invention includes a local light source, a 90° hybrid circuit, an optoelectronic converter, an analog to digital converter, and a digital signal processing unit; wherein the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components; the optoelectronic converter detects the optical signals and outputs detected electrical signals; the analog to digital converter quantizes the detected electrical signals and outputs quantized signals; the digital signal processing unit includes a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and an FFT operation unit for performing a fas

Abstract: An optical receiver system is disclosed. The system includes a local oscillator, a mixer and a processor. The local oscillator is configured to generate a laser signal to indicate a selection of one of a plurality of channels. In addition, the mixer is configured to receive signals on the plurality of channels and to utilize the laser signal to distinguish the signal on the selected channel. Further, the processor is configured to maximize a power level difference between the laser signal and at least one of the plurality of channels based on a total number of the plurality of channels by adjusting the power of the laser signal input to the mixer to limit a noise penalty in the receiver system.

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: In accordance with some embodiments of the present disclosure a method for receiving and processing an optical orthogonal frequency-division multiplexed signal containing a plurality of traffics comprises receiving the optical orthogonal frequency-division multiplexed signal.

Abstract: A receiving apparatus and method for processing a differential phase shift keying signal carrying a plurality of symbols are disclosed to provide for improved compensation of linear and non-linear noise in phase modulated optical transmission. The receiving apparatus comprises an input unit for receiving electrical signals derived from an optical signal and a calculation unit for calculating a current value of a decision variable. The current value is indicative of a differential phase shift in the optical signal between a currently received symbol and a previously received symbol as a function of the optical signal power of the optical signal for the currently received symbol and at least one previous value of the decision variable. The receiving apparatus also comprises a decision unit for determining the differential phase shift from the current value of the decision variable obtained from the calculation unit to obtain the currently received symbol.

Abstract: A coherent optical receiver circuit is disclosed in which various components of the optical receiver may be provided or integrated, in one example, on a common substrate. Further integration is achieved by incorporating various optical demultiplexer designs that are relatively compact and conserve space on the surface of the substrate. The optical receiver circuit may be used to demultiplex quadrature phase shift keying (QPSK) optical signals.

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: Methods and systems for normalized least mean square phase estimation are shown that include receiving optical transmissions that include a modulated signal, determining a step size based on a signal-to-noise ratio (SNR) and a laser linewidth that provides a balance between convergence speed and precision, estimating phase error using the determined step size, derotating the modulated signal to remove the estimated phase error, and demodulating the derotated signal to produce a bitstream.

Abstract: An optical receiver includes: a waveform distortion compensator to perform an operation on digital signal representing an optical signal generated by an A/D converter to compensate for waveform distortion of the optical signal; a phase detector to generate phase information representing sampling phase of the A/D converter; a phase adjuster to generate digital signal representing an optical signal in which the sampling phase of the A/D converter is adjusted from an output signal of the waveform distortion compensator using the phase information; a demodulator to generate a demodulated signal from the output signal of the phase adjuster; a phase controller to control the sampling phase of the A/D converter; a peak detector to detect a peak value of the phase information while the sampling phase of the A/D converter is controlled by the phase controller; and a compensation controller to control the waveform distortion compensator using the peak value.

Abstract: This application relates to an apparatus and a method for equalizing chromatic dispersion and a digital coherent optical receiver. The apparatus for equalizing chromatic dispersion comprising: a chromatic dispersion equalizing unit, for compensating chromatic dispersion of an input signal; and an additional time delay removing unit, for removing, in accordance with frequency offset of the input signal, chromatic dispersion equalization time delay generated by the chromatic dispersion equalizing unit.

Abstract: Distortion of a reception signal which is attributable to interference between subcarriers during photoelectric conversion is reduced in an optical OFDM communication system without broadening the signal band. A transmission signal processing unit (100) in a transmitter is provided with a distortion generating circuit (distortion generating unit) (170). A subcarrier signal is utilized as an input signal for the circuit. The distortion generating circuit (170) generates a baseband OFDM signal by means of inverse FFT calculation using the input signal, computes the square of the absolute value of the signal, and restores the subcarrier signal by mean of FFT calculation. Because interference between subcarriers is also included in the signal, the distortion element generated by the interference between the subcarriers can be extracted when the difference from the input signal is found.

Abstract: A reception device includes at least a light receiving unit, a phase calculation unit, and a demodulation unit. The light receiving unit receives intensity-modulated light from a transmission device. The transmission device executes phase modulation to a bit stream as an object to be transmitted and emits the intensity-modulated light which has an intensity changing at a preset time cycle and a phase changing in response to the phase modulation, and the phase is maintained during M cycles. The phase calculation unit detects the intensity of the intensity-modulated light p times per cycle of the intensity-modulated light and repeatedly calculates the phase of the intensity-modulated light on the basis of a result of the detection. The demodulation unit executes demodulation, which corresponds to the phase modulation, to the phase calculated by the phase calculation unit, and generates transmitted bit stream.

Abstract: A digital version of both amplitude and phase of at least one generic polarization component of a received optical signal is developed using dual-polarization direct differential detection with digital signal processing. The received signal is split into orthogonal polarization components, each of which is split into three copies. For each orthogonal polarization component a) an intensity profile is conventionally obtained using a copy and b) phase information is obtained by supplying each remaining copy to a respective one of a pair of optical delay interferometers having orthogonal phase offsets, followed by respective balanced intensity detectors. The outputs the balanced intensity detectors and the intensity profiles are converted into digital representations and used to develop, via signal processing, the optical field information of at least one generic polarization component of the received optical signal. Compensation of impairments, such as PMD, is realized through further processing.

Abstract: In order to reduce the size and simplify the structure of a coherent light receiver, the coherent light receiver includes an optical mixer for coupling local oscillator light and reception signal light, a photoelectric converter for photoelectrically converting light coupled in the optical mixer, a reception data processing unit for extracting reception data included in the reception signal light through digital signal processing for processing the coupled signal converted into an electrical signal by the photoelectric converter, based on a first clock, and a modulator for modulating the local oscillator light or the reception signal light inputted to the optical mixer respectively, by using a clock phase-synchronized with the first clock used for the digital signal processing in the reception data processing unit.

Abstract: A method for enabling bidirectional data communication using a single optical carrier and a single laser source with the aid of an integrated, colorless demodulator and detector for frequency modulated signals, and a reflective modulator. A receiving optical system holds a technique for demodulation and detection of optical frequency modulated signals, enabling remodulation of the incoming signal to establish bidirectional communication with the transmitting optical system, without introducing a high penalty. A colorless demodulator and detector, which provides the functionality of a periodic filtering device for demodulation of the downstream, and also detection capability. The principle of operation of the CDD relies on the introduction of a comb transfer function with the help of a Semiconductor Optical Amplifier, by providing a reflected feedback signal to the CDD's active element.

Abstract: A method includes modulating lightwaves to provide first and second OFDM signal sidebands at a first polarization direction and first and second OFDM signal sidebands at a second polarization direction, and combining sidebands that are oppositely positioned and joined from the first and second OFDM signal sidebands at each polarization direction to provide a polarization multiplexing OFDM signal.

Abstract: The present invention provides a frequency offset monitoring device and an optical coherent receiver. A low speed frequency offset monitoring device comprises a signal speed lowering section, for lowering the speed of an inputted signal and outputting the speed lowered signal, and a frequency offset monitor, for monitoring frequency offset of the speed lowered signal outputted by the signal speed lowering section.

Abstract: A self-polarization diversity technique to combat PMD in a direct-detection optical OFDM system. This technique does not require any dynamic polarization control, and can simultaneous compensate PMD in a WDM system with one device. Simulation results show that this technique virtually completely eliminates the PMD impairments in direct-detection optical OFDM systems.

Abstract: According to particular embodiments, a signal communicated from a transmitter to a receiver is received. A frequency offset estimate of the signal is determined. The frequency offset estimate indicates a frequency difference between the transmitter and the receiver. The frequency offset estimate is provided as feedback. A next frequency offset is compensated for according to the feedback.

Abstract: A digital coherent optical receiver provided with a 90-degree optical hybrid circuit for detecting an in-phase signal and a quadrature signal of an input optical signal, includes first through fourth circuits. The first circuit calculates a square of a sum of the in-phase signal and the quadrature signal. The second circuit subtracts a squared value of the in-phase signal and a squared value of the quadrature signal from the calculation result of the first circuit. The third circuit detects a phase error of the 90-degree optical hybrid circuit based on the calculation result of the second circuit. The fourth circuit corrects at least one of the in-phase signal and the quadrature signal according to the phase error detected by the third circuit.

Abstract: In a synchronous circuit, a synchronizing signal generator combines either an optical BPSK signal or local oscillation light with a phase-shifted signal to produce different optical signals, one of which for use in producing a signal demodulated from the BPSK signal is square-law detected, and calculates the optical signal detected to convert the signal into an electric signal. The generator produces an electric phase-locking signal which will be a demodulated signal from the BPSK signal on the basis of the electric signal. The phase-locking signal is used as a modulating signal by an intensity-modulating circuit to modulate an incident continuous light into an optical intensity-modulated signal, which is optoelectrically converted and square-law detected by an optoelectric converter. The converted signal is used by an optical VCO circuit as a phase error signal to adjust the phase or frequency of the local oscillation light, which is supplied to the signal generator.

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: A device and method are disclosed for blind equalization of an optical signal to implement adaptive polarization recovery, Polarization Mode Dispersion (PMD) compensation, and residual Chromatic Dispersion (CD) compensation in a digital coherent optical communication system.

Abstract: An optical beam synthesizer formed on a single chip is provided. It allows M-PSK modulation for both beam polarizations. The synthesizer comprises an optical pulse shaper and two M-PSK modulators for each polarization. A single-chip-integrated analyzer is provided to receive a modulated data. Analyzer comprises a pulse shaper operating as an optical sampler and a pair of 90-degrees optical hybrids for each polarization. Each optical hybrids mix incoming portions of the modulated beams with portions of the local oscillator beams. Both the synthesizer and the analyzer include a set of mirrors located on the back and front surfaces of the chips to create compact designs. The output beams from the analyzer are detected by a set of balanced photodiodes, and the data is recovered. It is another object of the invention to provide a communication system for data transmission having the synthesizer and the analyzer.

Abstract: A light receiving circuit includes: a light receiving element that receives an optical signal and converts into an electrical signal; a comparator that demodulates the information on the optical signal to a pulsed signal; a band limit circuit disposed between the light receiving element and the comparator, the band limit circuit removing noise components of frequency higher than the pulsed signal; and a comparator threshold circuit disposed between the light receiving element and the comparator, the comparator threshold circuit generating a threshold of the comparator and limiting the threshold of the comparator within a binary range.

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: An optical receiver and a method of demodulating an optical signal. The method includes combining a received optical signal with a local oscillator signal to construct a complex signal indicative of an optical field of the modulated optical signal and processing the complex signal recursively under control of a Kalman filter that enforces a constraint. The receiver includes an optical hybrid that combines a received optical signal with a local oscillator signal, a detector that recovers components of a complex signal, a processor that receives these components, and instructions that cause the processor to process the components of the complex signal recursively under control of a Kalman filter that enforces a constraint to recover data.

Abstract: Embodiments for optical communication are provided in which subbands of a multi-carrier optical signal are digital coherent detected and then processed to recover data carried by the modulated carriers corresponding to at least one of the subbands. An exemplary optical communication system includes a multi-carrier coherent optical receiver for receiving a multi-carrier optical signal having M modulated carriers that are frequency locked, wherein M is greater than 2. The multi-carrier coherent optical receiver includes a subband digital coherent detector configured to provide output signals in a digital form for N different subbands of the multi-carrier optical signal, where N is an integer greater than 1 and less than M; and a digital signal processor configured to process the digital form of the detected output signals in order to recover the data carried by the modulated carriers corresponding to at least one of the subbands of the multicarrier optical signal.

Abstract: In a quantum cryptography communication apparatus, a light pulse is generated by a light source and split into a signal light pulse and a reference light pulse on a receiving side. The signal light pulse and the reference light pulse are transmitted to a sending side via a communication channel. On the sending side, the received reference light is passed through a first optical path and phase-modulated by a randomly selected amount. Communication information is acquired on the basis of the reference light passed through the first optical path and the signal light passed via a second optical path. Frequencies of the signal light pulse and the reference light pulse are shifted. The intensity of the signal light pulses is attenuated and phase-modulated by an amount corresponding to the communication information. The resultant signal light pulse and the reference light pulse are returned back to the receiving side.

Abstract: An optical receiver for stably reproducing packets having different light receiving levels is disclosed. The optical receiver includes: a light receiving element for outputting a current in response to a light receiving level of an optical signal; a preamplifier for converting the current signal outputted from the light receiving element into a voltage signal; a circuit for detecting a consecutive same binary symbols portion from a binary symbols stream of the voltage signal outputted from the preamplifier to output a time constant switching signal in response to a detection result thereof; a level detecting circuit for detecting a voltage level of the voltage signal outputted from the preamplifier based upon a time constant which is switched/controlled in response to the time constant switching signal; and an amplifier for amplifying an output voltage of the level detecting circuit to apply a control voltage for controlling the gain to the preamplifier.

Abstract: An optical homodyne communication system and method in which a side carrier is transmitted along with data bands in an optical data signal, and upon reception, the side carrier is boosted, shifted to the center of the data bands, and its polarization state is matched to the polarization state of the respective data bands to compensate for polarization mode dispersion during transmission. By shifting a boosted side carrier to the center of the data bands, and by simultaneously compensating for the effects of polarization mode dispersion, the provided system and method simulate the advantages of homodyne reception using a local oscillator. The deleterious effects of chromatic dispersion on the data signals within the data bands are also compensated for by applying a corrective function to the data signals which precisely counteracts the effects of chromatic dispersion.

Abstract: The present invention relates to a coherent optical communication apparatus and method. According to the invention, the optical communication apparatus receives a modulated optical signal, which is generated by modulating an optical signal with a first electrical signal obtained by adding a second electrical signal carrying information to be transmitted and a reference electrical signal, and converts the modulated optical signal to a third electrical signal by coherent detection. Then the apparatus detects an amount of fluctuation of the reference electrical signal included in the third electrical signal, and compensates the second electrical signal included in the third electrical signal using the amount of fluctuation.

Abstract: The present invention discloses an optical coherent receiver, and a frequency offset estimating apparatus and a frequency offset estimating method for use in the optical coherent receiver. The optical coherent receiver includes a front end processing section for changing an optical signal into a base band digital electric signal.

Abstract: A heterodyne receiver includes first and second laser sources such as laser diodes which generate optical receiver oscillator (RO) signals having respective RO frequencies. Temperature control circuitry controls a temperature difference between the operating temperatures of the sources such that the RO frequencies differ by a difference frequency corresponding to the temperature difference, the difference frequency being offset from a frequency of a modulated millimeter-wave signal by a predetermined intermediate frequency. An electro-optical nonlinear mixer such as a photodiode receives the optical RO signals and the modulated millimeter-wave signal and generates an electrical intermediate-frequency (IF) signal, which is provided to an electrical amplifier/detector to detect the output signal corresponding to the modulation of the modulated millimeter-wave signal.

Abstract: An optical reception device realizes stabilization of reception sensitivity inexpensively and highly precisely. The optical reception device includes: a Mach-Zehnder type 1-bit delay unit including a one-terminal input port and two-terminal output ports for decoding an optical difference phase shift keying (DPSK) signal and provided with one or more phase control functions to control the phase state of light; photoelectric conversion means for branching a portion of an optical output signal output from the one-side output port of the Mach-Zehnder type 1-bit delay unit, to convert the branched portion into an electric signal; and a phase control unit for controlling the phase state of the Mach-Zehnder type 1-bit delay device by using as an error signal the output signal of the photoelectric conversion means.

Abstract: An apparatus and method for reducing electrical signal intermodulation by processing a balanced electrical signal in the optical domain in a manner adapted to reduce noise and second order intermodulation, and converting the processed optical signal back to an electrical domain signal with either a single or balanced (differential) outputs.

Abstract: [Object] It is to raise operational frequency and S/N ratio of the pulsed homodyne detector to measure the quadrature amplitude of the signal pulse light. [Solution] The local pulse light in telecom band is yielded at repetition rate of 80 MHz. Two output lights are generated by interference of the local pulse light and the signal pulse light. The first photodiode and the second photodiode are connected differentially. The first photodiode converts one side output light to an electric signal. The second photodiode converts the other side output light to another electric signal. The M-derived low-pass filter eliminates the third harmonics of the local pulse light. Moreover, the higher frequency components than triple frequency of the repetition rate are eliminated. In this way, even when it is operated at high repetition rate of 80 MHz at maximum, the quadrature amplitude of the signal pulse light can be measured with high quantum efficiency of about 90% and with S/N ratio of more than 10 dB.

Abstract: A photodiode receives an infrared signal transmitted from a transmitter. A current distributing unit outputs a detection current Id output from the photodiode as a first detection current Id1 and a second detection current Id2 to a subsequent first current-to-voltage conversion amplifier and a subsequent second current-to-voltage conversion amplifier respectively. The first and second current-to-voltage conversion amplifiers convert the detection currents into voltages with current-to-voltage conversion gains g1 and g2. The current-to-voltage conversion gains g1 and g2 of the first and second current-to-voltage conversion amplifiers are set such that ranges of signal levels in which the distributed detection currents Id1 and Id2 can significantly be amplified differ from each other.

Abstract: An optical receiver includes an optical detector that generates a photocurrent at an output. A transimpedance amplifier generates an amplified voltage signal corresponding to the photocurrent generated by the optical detector. An offset voltage generator generates an offset voltage that biases the voltage signal generated by the transimpedance amplifier. A switch having a first input electrically connected to the output of the transimpedance amplifier and a second input electrically connected to the output of the offset voltage generator switches between the offset voltage and the voltage signal generated by the transimpedance amplifier.

Abstract: The present invention is a differential M phase shift keying optical receiving circuit to improve an identification property of a signal from an optical front-end unit having a plurality of lines. For this, the differential M phase shift keying optical receiving circuit includes: a light-electricity converter for outputting a plurality of electronic signals in which phase-modulated element is intensity modulated from a received optical signal; a data reproduction unit for reproducing a plurality of data signals synchronized with a common clock signal from the plurality of electronic signals output from the light-electricity converter; a clock signal generation unit for generating the common clock signal to be used for reproducing the plurality of data signals in the data reproduction unit with the use of one of the plurality of electronic signals output from the light-electricity converter; and a selection unit for selecting an electronic signal to be used for generating the common clock signal.

Abstract: One aspect of the invention is a homodyne coherent receiver, suitable for high speed phase shift keying (PSK), the receiver comprising a receiver for receiving an incoming signal having a carrier-less modulation format, a signal conditioning sub-system that generates a carrier component from the incoming signal, and an optical injection phase locked loop (OIPLL) that phase locks the generated carrier component of the incoming signal. Embodiments of the invention may enable DSP free detection of optical PSK signals, which may be required in next generation fiber transmission systems and in optical constellation analyzer systems. In addition, embodiments of the invention may provide improved receiver sensitivity performance comparing to prior art systems using direct detection schemes. Also, embodiments of the invention may be advantageous in terms of cost and energy efficiency.

Abstract: The invention provides a system and method for secure communication that involves encoding and transmitting an optical communications signal that is encoded based on a multi-dimensional encoding technique. This technique may include at least one or more of encoding a phase, a polarization, and a frequency of the signal. Light encoding is independent from its modulation with data. The data is modulated using any format; in the preferred embodiment the QPSK format is implemented. The encoded and modulated light is transmitted through free space or via a fiber optic network to a receiver, where the information is decoded. A coherent detection based on 90-degrees or 120-degrees optical hybrid is used to decode and recover the data from the received signal. Because the encoding of the transmitted light varies according to a specific pattern or sequence, one without knowledge of the transmission encoding sequence is prevented from decoding the transmitted information.

Abstract: In one embodiment, a down conversion receiver is provided for a phase modulated optical signal. This may include an optical coupler coupled to be capable of receiving a phase modulated signal and a local oscillator signal, and a modulator coupled to an input of the optical coupler so as to be capable of modulating one of: (1) a phase modulated signal; or (2) a local oscillator signal. A photodetector circuit is located to be capable of detecting signals coupled by the optical coupler, with a sub-band selector circuit coupled to be capable of receiving signals from the photodetector circuit. The sub-band selector circuit has an output coupled to a modulating input of the modulator.

Abstract: Methods and systems for compensating a frequency mismatch ?f between a local Oscillator (LO) of a coherent optical receiver and a carrier of a received optical signal. An average frequency of the LO is controlled to compensate at least long-period variations of the frequency mismatch. An electrical carrier recovery circuit for compensating short period variations of the frequency mismatch.

Abstract: According to one embodiment, an infrared signal decode circuit includes: a comparator; a correlation signal generator generating a sum of a first detection signal and a second detection signal as a correlation signal, the first detection signal being obtained by performing an absolute value calculation on a first correlation signal, the second detection signal being obtained by performing an absolute value calculation on a second correlation signal, the first correlation signal corresponding to a correlation between a binary signal and a first reference signal with a frequency substantially identical to a base frequency of a subcarrier of an infrared signal, the second correlation signal corresponding to a correlation between the binary signal and a second reference signal with a phase that differ from a phase of the first reference signal by 90 degrees; and a decoder binarizing the correlation signal generated by the correlation signal generator.