Abstract: Provided are methods for optical communication, comprising: generating a phase difference signal with heterodyne or homodyne phase-locked-loop (PLL) from between an optical input signal and a local laser source; controlling the local laser source with the phase difference signal; demodulating the optical input signal using the local laser source as a carrier signal to generate a baseband output signal; and controlling the heterodyne or homodyne PLL and the demodulation with an electrical oscillator signal. Also provided are related methods.

Abstract: The present invention provides an optical phase synchronization method characterized by involving applying a small phase modulation signal (dither signal) to local oscillator light, acquiring an error signal that is dependent on a phase shift, and controlling the phase shift. The present invention further provides an optical phase synchronization method characterized by involving inducing a specific phase pattern in dummy pulses in an optical resonator using injection light, applying phase modulation to the local oscillator light, and thereby acquiring a part of the measurement result of the dummy pulses as the error signal. The present invention is further characterized by arranging calculation pulses and phase synchronization dummy pulses in a distributed manner (for example, alternately) and increasing a pulse width using a narrow band electrical filter.

Abstract: A method for correcting a phase jump caused by polarization-induced fading in optical fiber phase demodulation, including the steps of: 1, selecting a demodulated phase in the case of non-depolarization as historical sample data; 2, determining an autoregressive coefficient and a moving average coefficient of the autoregressive moving average model for the demodulated phase; 3, establishing a Kalman prediction model for the demodulated phase, and deriving recursive equations of the Kalman prediction model for the demodulated phase; and 4, judging whether a jump point exists in the actual demodulated phase, determining polarization states of lights if the jump point exists, and correcting the jump point when the polarization states of the lights are in polarization orthogonality by replacing the actual demodulated phase with a predicted phase value. The disclosure ensures the correctness of subsequent vibration-based signal processing.

Abstract: An optical transmission apparatus includes a wavelength variable filter whose transmission light wavelength is variable; a receiver that receives light, the light being sent from another optical transmission apparatus and passing through the wavelength variable filter; a transmitter that sends to the another optical transmission apparatus, a utilization permission request for a second wavelength corresponding to a first wavelength of the light received by the receiver, the transmitter sending the utilization permission request as light of the second wavelength and in a form of a tone signal of a predetermined frequency; and a controller that, when receiving from the another optical transmission apparatus, a utilization permission notification of the second wavelength for a sender of the utilization permission request, configures a wavelength of a main signal to the second wavelength, the main signal being sent from the transmitter to the another optical transmission apparatus.

Abstract: Systems and methods for reducing variance in reach of wavelength division multiplexed (WDM) channels in optical transport networks may include selecting, for each channel assigned to a respective wavelength, an initial modulation format and an initial distribution of constellation points in the complex plane, determining a target reach for all WDM channels that is achievable by higher wavelength channels but not by shorter wavelength channels, and applying one or more reach extension techniques to at least one shorter wavelength channel but not to the higher wavelength channels. The reach extension techniques may include probabilistic constellation shaping, symbol rate optimized subcarrier multiplexing, or a combination of the two. Transponders may be configurable to transmit or receive traffic over the WDM channels with or without implementing the reach extension techniques, as applicable.

Abstract: The present invention relates to adding and dropping signals in a node of an optical network, wherein the node includes a reconfigurable optical add/drop multiplexer (ROADM). The reconfigurable optical add/drop multiplexer (ROADM) comprises output ports and at least one add port connectable to at least one line interface of the network and adapted to receive a modulated optical signal from the line interface. Selection units are connected to one of said add ports and adapted to forward the respective signals to a selected output terminal. A plurality of broadcast units is adapted to broadcast signals forwarded by the selection. Then a multiplexing and selecting device or apparatus selects and multiplexes the optical signals broadcast via broadcast unit output terminals into a plurality of wavelength-division multiplexing (WDM) optical signals and forwards the same to output ports of the reconfigurable optical add-drop multiplexer (ROADM).

Abstract: An optical measuring device is configured to measure a light beam emitted from a light source. The optical measuring device includes a light collecting element, at least four light-sensing elements, a light splitting device, and at least one lens. The light collecting element is configured to collect the light beam. The light-sensing elements are configured to respectively sense the light fields of different light paths of the light beam. The respective distances of the light paths between the respective light-sensing elements and the light source are different from each other. The light splitting device is configured to split the light beam passing through the light collecting element and respectively guide the split light beams to the light sensing elements. The lens is disposed between at least one of the light-sensing elements and the light collecting element, and is configured to form images on the at least four light-sensing elements.

Abstract: A method for data processing of an optical network unit is provided, the method comprising the steps of receiving a configuration information at the optical network unit, adjusting a light signal to a wavelength or wavelength range indicated by the configuration information, demodulating an incoming optical signal by means of the light signal, mixing the demodulated incoming optical signal with a signal generated by an oscillator and generating a modulated optical upstream signal modulating the light signal by means of a software radio, so that the resulting optical upstream frequency can be shifted with respect to the frequency of the local oscillator by a programmable amount. Furthermore, an according device and a communication system are suggested comprising at least one such device.

Abstract: A measuring method and apparatus of frequency response characteristic imbalance of an optical receiver, in which by transmitting at least one single-frequency signal in an I branch or a Q branch of an optical transmitter, an amplitude ratio and phase imbalance of the I branch and the Q branch of the optical receiver are directly calculated according to at least one pair of received signals extracted from the I branch and the Q branch of the optical receiver of which frequencies are split due to a frequency difference between lasers of the optical transmitter and the optical receiver, with no need of many times of changes of central wavelengths of lasers of the optical transmitter and the optical receiver for performing measurement for many times, and measurement of frequency response characteristic imbalance of the optical receiver may be achieved through one time of measurement, which is simple in process and accurate in measurement result.

Abstract: A multi-wavelength passive optical network (MW-PON) includes an optical distribution network (ODN), a plurality of optical line terminations (OLTs) and an optical network unit (ONU). The ODN includes a trunk fiber, one or more branching elements, and a plurality of distribution fibers. Each OLT is associated with an individual bi-directional wavelength channel using a corresponding single downstream wavelength and a corresponding single upstream wavelength, and supporting a specific downstream line rate and one or more distinct upstream line rates. The ONU is communicatively coupled to a respective distribution fiber, being tunable over a specific range of downstream wavelengths and a specific range of upstream wavelengths, and supporting a specific downstream line rate and a specific upstream line rate.

Abstract: An apparatus and a method for monitoring in-band OSNR (Optical Signal-to-Noise Ratio) which monitors the in-band OSNR by using two parallel Mach-Zehnder-interferometers with different optical time delays are disclosed. The apparatus and method can be resistant to chromatic dispersion, polarization mode dispersion and polarized noise, can measure the coherence characteristics of the signal without removing the noise, and can be manufactured into a semiconductor integrated device and be applied in the future high-speed optical network.

Abstract: An optical signal is received at a coherent optical receiver. The received optical signal is converted to a first electrical signal and a second electrical signal through a first photodetector and a second photodetector, respectively. The first electrical signal is input into a first single input variable gain amplifier, and the second electrical signal is input into a second single input variable gain amplifier. A gain of at least one of the first single input variable gain amplifier or the second single input variable gain amplifier is controlled to balance the output of the first single input variable gain amplifier and the output of the second single input variable gain amplifier. The output of the first single input variable gain amplifier and the output of the second single input variable gain amplifier are input into a differential amplifier. A receiver output is obtained at an output of the differential amplifier.

Abstract: A coherent optical receiver that receives an optical PSK-modulated signal includes optical elements that combine the optical PSK-modulated signal and an optical local-oscillating (LO) signal and splits the combined optical signals into multiple parts that have a predefined phase offset relative to one another. The receiver further includes at least one thyristor and control circuitry operably coupled to terminals of the at least one thyristor. The control circuitry is configured to receive the multiple parts of the combined optical signals and controls switching operation of the at least one thyristor according to phase offset of optical PSK-modulated signal relative to the optical LO signal.

Abstract: A receiver configured to receive wave packets encoded with data via a nonlinear channel is disclosed. The receiver includes an input configured to receive the wave packets from the non-linear channel. The receiver also includes a processor configured to generate a transfer matrix from the received wave packets and find the representation of the transfer matrix as ratios of polynomials and compute the non-linear Fourier spectrum in which the data has been embedded. The receiver may also include a demodulator configured to demodulate the non-linear Fourier spectrum to recover the data. Periodic boundary conditions may be selected. Boundary conditions may be selected based on a non-periodic vanishing signal. The received wave packets may be configured as solitons. The nonlinear channel may be an optical channel.

Abstract: A sensing system includes plurality of sensors along the lengths of input and output optical fibers. Each sensor receives broadband pulses from the input fiber, dynamically senses a plurality of physical parameters in a one-to-one correspondence with a plurality of predefined wavelength bands, and forms signal pulses from the broadband pulses by transmitting only a single wavelength within each wavelength band. Each single wavelength has a dynamically-varying peak wavelength value indicative of the corresponding sensed physical parameter. The signal pulses from the output optical fiber are directed into one or more interferometers, which produce a phase deviation corresponding to each dynamically-varying peak wavelength value.

Abstract: A system for communication between two communication platforms, including a near-earth returning platform and a remote platform. A bidirectional asymmetrical communication link is set up between the two platforms.

Abstract: Described herein are systems and methods for accurately estimating and removing a carrier frequency offset. One exemplary embodiment relates to a system comprising a frequency offset detection circuit detecting a carrier frequency offset in an optical signal, and a frequency testing circuit calculating an estimated frequency offset value of the carrier frequency offset, wherein the frequency testing circuit removes a carrier phase based on the estimated frequency offset value and recovers the optical signal. Another exemplary embodiment relates to a method comprising detecting a carrier frequency offset in an optical signal, calculating an estimated frequency offset value of the carrier frequency offset, removing a carrier phase based on the estimated frequency offset value, and recovering the optical signal.

Abstract: An optical component contains a tunable laser. The tunable laser provides an optical local oscillator signal, and the tunable laser is directly modulated to provide a modulated optical data signal. In this manner we have optimization of the channel wavelength and obtain an optimized electrical and optical bandwidth utilization. Furthermore, a method for data processing is suggested.

Abstract: A coherent optical receiver according to an exemplary aspect of the present invention includes a coherent optical receiving unit, a first waveform equalizing circuit compensating waveform distortion caused by characteristics of the coherent optical receiving unit and compensating chromatic dispersion in a predetermined range to an input signal, a second waveform equalizing circuit compensating chromatic dispersion of the input signal, and a controller monitoring a chromatic dispersion amount of the input signal and controlling a compensation coefficient regarding the chromatic dispersion compensation performed by each of the first waveform equalizing circuit and the second waveform equalizing circuit depending on the chromatic dispersion amount to be compensated.

Abstract: Consistent with an aspect of the present disclosure, an optical signal carrying data or information is supplied to photodetector circuitry that generates a corresponding analog signal. The analog signal may be amplified or otherwise processed and supplied to analog-to-digital conversion (ADC) circuitry, which samples the analog signal to provide a plurality of digital signals or samples. The timing of such sampling is in accordance with a clock signal supplied to the ADC circuitry. A phase detector is provided that detects and adjust the clock signal to have a desired phase based on frequency domain data that is output from a Fast Fourier transform (FFT) circuit that receives the digital samples. Preferably, the phase detector circuit is configured such that it need not receive all the frequency domain data output from the FFT at any given time in order to determine the clock phase.

Abstract: The present invention provides a signal detection method, including: receiving, by a frequency mixer, wavelength division multiplexing signals and a local oscillator signal, where a wavelength of the local oscillator signal and a wavelength of a target signal in the wavelength division multiplexing signals are the same; a frequency mixer performs interference on the wavelength division multiplexing signals through the local oscillator signal to obtain a coherent signal formed by the local oscillator signal and the target signal; sending the coherent signal to a transimpedance amplifier for amplification to obtain a voltage signal; and obtaining the power of the target signal according to a power amplitude of the voltage signal.

Abstract: A method of recovering frequency and phase associated with an optical carrier signal in an optical communication system includes determining an estimated frequency offset based on a starting training sequence, determining a current frequency offset based on the estimated frequency offset and a current phase during steady-state operation of the optical communication system, determining a current frequency based on the current frequency offset, determining an estimated phase using training symbols inserted into the optical carrier signal, and determining the current phase associated with the optical carrier signal based on the estimated phase and a blind phase search algorithm. A corresponding systems and computer-readable device are also disclosed.

Abstract: An optical transport system that transmits data using relatively short FEC-encoded data frames. The corresponding modulated optical signals are decoded at an optical receiver using frame-based maximum likelihood sequence estimation that relies on data redundancy present in each FEC-encoded data frame for the determination of its source bits. In some embodiments, the modulated optical signals carrying the FEC-encoded data frames are generated using a polarization-division-multiplexed constellation. The FEC-coding rate and frame length can be adjusted without changing the constellation, which advantageously enables the optical transport system to dynamically adapt its transmission format to the changing link conditions in a manner that results in better overall receiver sensitivity than that achieved with comparable bit-rate-adaptation methods that rely on a constellation change rather than on a change of the FEC-coding rate.

Abstract: A receiver that includes a carrier recovery module that includes a reference signal generator that is arranged to generate a reference signal that estimates a carrier signal; a decision module that is arranged to demodulate a receiver input signal by the reference signal to provide a demodulated signal and to evaluate the demodulated signal to provide an decision module output signal that estimates the carrier signal; the reference signal generator includes a delay and rotation module that is arranged to delay receiver input signals to provide delayed receiver input signals and to align the delayed receiver input signals by a rotation that is responsive to the decision module output signal thereby providing aligned signals; and a multiplication and summation module that is arranged to generate the reference signal by calculating a weighted sum of the aligned signals.

Abstract: A receiver includes: an extraction circuit to extract a phase fluctuation component common to phase data of two polarization components that are separated in a coherent reception of a polarization multiplexing phase modulation optical signal; and a correction circuit to correct the phase data of the two polarization components in accordance with the phase fluctuation component.

Abstract: A digitally locking coherent receiver and a method of coherently receiving a data signal. One embodiment of the receiver includes: (1) a detector configured to recover a composite signal with respect to a local oscillator signal, the composite signal being a combination of a data signal and a reference signal, and (2) a digital signal processor (DSP) communicably coupled to the detector and configured to recognize and compensate for drift in the local oscillator signal with respect to the reference signal.

Abstract: This disclosure describes the Fast Chromatic Dispersion Estimation (FCDE) techniques which corrects for chromatic dispersion in high data rate optical communications systems such as some coherent optical communications systems. FCDE may utilize transform such as fast-Fourier transforms to estimate the chromatic dispersion. From an estimation of the chromatic dispersion, the techniques may determine filter tap coefficients for compensating the chromatic dispersion.

Abstract: A ultra high speed photonic Analog to Digital Converted (ADC) for sampling and quantizing an electrical voltage signal, internally enabled by photonics uses coherent optical detection architectures for photonic quantization. Coherent light is phase modulated by the test signal. Using an interferometer, or an array of interferometers the phase of modulated light is compared with a reference light. Flash ADC, successive approximation ADC and delta-sigma ADC configurations are presented.

Abstract: A system and method for generating soft decision reliability information from hard decisions in an optical signal receiver. The receiver may include a digital signal processor including a symbol reliability function for generating symbol reliability information associated with symbols encoded on optical signal. The symbol reliability information may be generated as a function of the symbols and hard decision outputs associated with the symbols.

Abstract: In part, aspects of the invention relate to methods, apparatus, and systems for intensity and/or pattern line noise reduction in a data collection system such as an optical coherence tomography system that uses an electromagnetic radiation source and interferometric principles. In one embodiment, the noise is intensity noise or line pattern noise and the source is a laser such as a swept laser. One or more attenuators responsive to one or more control signals can be used in conjunction with an analog or digital feedback network in one embodiment.

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: Methods and systems of data symbol recovery in a coherent optical receiver of an optical communications system. A respective probabilistic phase error is calculated for each of a plurality of data symbol estimates. A phase rotation is calculated based on the probabilistic phase error estimates, using a filter function, and the phase rotation applied to at least one data symbol estimate to generate a corresponding rotated symbol estimate. Each rotated symbol estimate is processed to generate corresponding decision values of each data symbol.

Abstract: Consistent with the present disclosure, a portion of light output from a laser, such as a local oscillator laser, is supplied to an optical circuit. The optical circuit may include a delay line interferometer that supplies a further optical signal that is sensed by a photodetector circuit. Alternatively, a 90 degree optical hybrid may be provided which receives two inputs whereby one input is delayed relative to the other input. The outputs of the optical hybrid are also supplied to a photodetector circuit. An electrical signal output from the photodetector circuit is indicative of changes in phase of the light output from the laser. A processor circuit may be configured to process the electrical signal to determine an accumulated phase of the laser light based on the electrical signal. Alternatively, based on the electrical signal, phase offset values may be obtained to offset or compensate local oscillator phase noise.

Abstract: An optical module for receiving light according to a digital coherent optical transmission scheme includes two optical fibers, and a monitor PD. The optical signal processing circuit includes a substrate, an optical waveguide layer made up of a core and a clad layer stacked on top of the substrate, and fixtures stacked on top of the clad layer on the one end, and is provided with a light shield member which spans the substrate, the clad layer, and the edge face of the fixture on the edge face of the optical signal processing circuit that faces the monitor PD, and which includes an aperture unit aligned with the given site where the diverted signal light is output.

Abstract: This disclosure relates to an optical receiver arrangement (500) and a method for receiving a multichannel optical signal OB in an optical receiver arrangement (500), wherein the optical signal OB comprises a number of optical channels A, B, C, D equally distributed around an optical carrier frequency fLO and wherein the optical receiver arrangement (500) comprises an optical homodyne receiver (200) and a multichannel recovery unit (300).

Abstract: A device able to evaluate a phase difference between I-component and Q-component of signal light generated by an optical hybrid is disclosed. The device includes a detector, a compensator and an evaluator. The detector detects positive and negative elements of each of the I-component and the Q-component. The compensator generates a compensated I-component and a compensated Q-component so as to keep the sum of positive and negative elements of each of components in constant. The evaluator determines the phase difference via an ellipsoid drawn by the compensated I- and Q-components.

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: 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 method for carrier frequency recovery in an optical coherent transmission system is provided in which at least one kind of equalization of a received signal is performed in frequency domain, the method comprising: performing a frequency offset compensation in frequency domain on a received signal according to an estimated value of the frequency offset; obtaining the signal with the frequency offset compensated. Further, an optical coherent receiver is provided comprising: an equalization unit, adapted to perform at least one kind of optical distortion compensation of a received signal in frequency domain; a frequency offset compensation unit, adapted to perform the frequency offset compensation in frequency domain on a received signal according to an estimated value of the frequency offset to obtain the signal with frequency offset compensated.

Abstract: One coherent optical receiver includes a 3×3 coupler for receiving a signal and a local oscillator into a first and a third input port respectively, and three detectors for detecting a respective output of the coupler to generate corresponding first, second and third detected signals. A detected signal is filtered by an Alternating Current (AC) coupler to generate a respective first, second or third filtered signal. An adder adds the first, the second and the third filtered signals to determine a directly detected signal term. A first subtractor subtracts the directly detected signal term from the first filtered signal to determine an in-phase signal. A second subtractor subtracts the directly detected signal term from the third filtered signal to determine a quadrature signal. A digital signal processor processes the in-phase signal and the quadrature signal to recover the optical signal.

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: Consistent with the present disclosure, a method and system for detecting a clock phase of an optical signal in a coherent receiver is provided that is insensitive to polarization mode dispersion (PMD) and other polarization effects in the optical communication system. The clock phase of the received signal is estimated by first calculating a phase shift between a pair of related frequency domain data outputs of a Fourier transform circuit. The calculated phase shift includes a phase component and a data spectrum component. The calculated phase shift is then averaged over a number of clock cycles to remove the data spectrum components thus enabling extraction of the phase component. A determinant function on the time averaged result is used to normalize any effects of PMD from the received signal and isolate the phase component. In this manner, the phase component is not dependent on the PMD effects in the optical communication system.

Abstract: An optical sampling arrangement for high-speed measurement of the time-varying electric field of an optical input signal utilizes coherent mixing of the optical input signal with a reference laser source in a phase-diverse optical hybrid solution, followed by optical sampling of the coherently-mixed fields at the output of the optical hybrid. The generated streams of optical samples are then detected and signal processed in order to reconstruct a sampled version of the electric field of the original optical input signal.

Abstract: A receiver for fiber optic communications.

Abstract: The sender and the receiver prepare two photons in the entangled state of polarization. The first photon of the two photons is sent to the sender and the second photon of the two photons is sent to the receiver. The sender measures the first photon after the first photon pass the polarizer in which the vertical polarized photon can pass, when the sender sends the signal “1”. The sender measures the first photon after the first photon pass the polarizer in which the 45 degrees polarized photon can pass, when the sender sends the signal “0”. The receiver measures the second photon by the balanced homodyne measurement. And, the receiver knows the signal from the absolute value of the result of the balanced homodyne measurement.

Abstract: A received optical signal is coherently demodulated and converted into electrical complex samples, which are dispersion compensated in a compensation filter. A control circuit calculates comparison values from corrected samples and an estimated error value. A plurality of compensation functions is applied according to a predetermined dispersion range and after a second iteration, the compensation filter is set to an optimum compensation function.

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: A signal transmission and reception device and method are provided. The transmission method comprises generating multiple optical carriers from a basic optical carrier; modulating optical carriers, except for a predetermined optical carrier, in the optical carriers by using multiple data signals respectively, to generate multiple optical modulated signals; and synthesizing the multiple optical modulated signals and the predetermined optical carrier into a single optical signal, and transmitting the signal.

Abstract: A receiving device includes a first conversion unit, an amplification unit, and a microcomputer. The microcomputer includes: a second conversion unit that performs, for each sampling time duration, AD conversion on a voltage signal into an AD-converted value; a first calculation unit that calculates a difference digital value by difference calculation; a second calculation unit that calculates a positive reference value and a negative reference value; a detection unit that detects a rising point starting difference digital values greater than the positive reference value, and a falling point starting difference digital values smaller than the negative reference value; a third calculation unit that calculates a first sample period and a second sample period; and a fourth calculation unit that calculates a modulated signal for each symbol time period based on the first sample period and the second sample period.

Abstract: An apparatus and method for extracting an optical clock signal are provided. The apparatus includes a first reflection filter selecting and reflecting only a first frequency component in an input optical signal; a first Fabry-Perot laser diode matching the first frequency component reflected by the first reflection filter with a predetermined output mode and outputting the first frequency component in the predetermined output mode; a second Fabry-Perot laser diode selecting a second frequency component in an input optical signal that has not been reflected but has been transmitted by the first reflection filter, matching the second frequency component with a predetermined output mode, and outputting the second frequency component in the predetermined output mode; and a photodetector receiving the first frequency component from the first Fabry-Perot laser diode and the second frequency component from the second Fabry-Perot laser diode and beating them to extract a clock signal.