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: To enable signal position detection, frequency offset compensation, clock offset compensation, and chromatic dispersion amount estimation in a communication system based on coherent detection using an optical signal, even on a signal having a great offset in an arrival time depending on a frequency due to chromatic dispersion. An optical signal transmitting apparatus generates specific frequency band signals having power concentrated on two or more specific frequencies and transmits a signal including the specific frequency band signals. An optical signal receiving apparatus converts a received signal into a digital signal, detects positions of the specific frequency band signals from the converted digital signal, estimates frequency positions of the detected specific frequency band signals, and detects a frequency offset between an optical signal receiving apparatus and an optical signal transmitting apparatus.

Abstract: A vehicle powering wireless receiver for use with a first electromagnetic resonator coupled to a power supply. The wireless receiver includes a load configured to power the drive system of a vehicle using electrical power, and a second electromagnetic resonator adapted to be housed upon the vehicle and configured to be coupled to the load, at least one other electromagnetic resonator configured with the first electromagnetic resonator and the second electromagnetic resonator in an array of electromagnetic resonators to distribute power over an area, wherein the second electromagnetic resonator is configured to be wirelessly coupled to the array to provide resonant, non-radiative wireless power to the second electromagnetic resonator from the first electromagnetic resonator.

Abstract: A method for phase noise mitigation for a coherent receiver in either an OFDM or single carrier based transmission system including applying a frequency offset and coarse phase noise compensation based on a radio frequency RF tone or using a phase lock loop PLL m-th power procedure, responsive to a signal from a digital signal processed transmission with an added pilots signal over an optical system, applying fine phase noise compensation based on comparison of the pilots signal in a time domain, removing the pilots, and demodulating the remaining pilotless signal.

Abstract: Data transmission method and apparatus utilizing color coding is disclosed. A one-to-one correspondence between a set of eight unique 3-bit data units and a set of eight unique color representations is established for color coding a sequence of 3-bit data units. Transmission of the sequence of 3-bit data units is then facilitated using a sequence of color representations, wherein each one of the sequence of 3-bit data units has a one-to-one correspondence with one of the sequence of color representations.

Abstract: A method and a Reconfigurable Optical Add Drop Multiplexer (ROADM) where blocking of a first optical signal carried over a specific optical channel in the ROADM is performed by compensating the first optical signal by a second optical signal created for that purpose.

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

Abstract: A light-receiving device array includes a photodiode array that is provided with plural light-receiving sections each of which includes a first conductivity type electrode and a second conductivity type electrode, and a carrier, wherein the carrier includes plural pair of electric lines each of which is formed from a first electric line connected to the first conductivity type electrode of each light-receiving section, and a second electric line connected to the second conductivity type electrode of the light-receiving section, a first ground electrode that extends between one pair of electric lines of the plural pair of electric lines and a pair of electric lines adjacent to the one pair of electric lines, and a second ground electrode that is formed on a part of the rear surface and is electrically connected to the first ground electrode.

Abstract: A method and system for a estimating a most likely location of a periodic SYNC burst within an optical signal received through an optical communications system. A cross-correlation is calculated between a multi-bit digital signal derived from the optical signal and a known symbol sequence of the SYNC burst. The cross-correlation is processed in at least one sub-block to identify a candidate sub-block in which the SYNC burst is most likely located. The candidate sub-block is then further analyzed to estimate a location of the SYCN burst.

Abstract: Aspects of the invention provide transmitters and receivers for managing multiple optical signals. High order modulation, such as phase and/or amplitude modulation, is used to achieve multiple bits per symbol by transporting multiple asynchronous data streams in an optical transport system. One or more supplemental multiplexing techniques such as time division multiplexing, polarization multiplexing and sub-carrier multiplexing may be used in conjunction with the high order modulation processing. This may be done in various combinations to realize a highly spectrally efficient multi-data stream transport mechanism. The system receives a number of asynchronous signals which are unframed and synchronized, and then reframed and tagged prior to the high order modulation. Differential encoding may also be performed. Upon reception of the multiplexed optical signal, the receiver circuitry may employ either direct detection without a local oscillator or coherent detection with a local oscillator.

Abstract: A polarization-multiplexed signal receiver includes a polarization adjustment unit to adjust a polarization state of inputted polarization-multiplexed signal, which is carrying signal data on each of two polarized waves being inputted, based on a control signal and to output the adjusted polarization-multiplexed signal, an optical signal reception unit to convert the polarization-multiplexed signal having the adjusted polarization state into an analog electric signal and output the analog electric signal, an A/D conversion unit to convert the analog electric signal into a digital electric signal and output the digital electric signal, a digital signal processing unit to perform digital coherent processing to the digital electric signal and take out the signal data and a feedback control unit to generate the control signal based on quality of the signal data and output the signal data to the polarization adjustment unit.

Abstract: In order to suppress occurrence of a code error which occurs when an optical receiver detects a signal over a wide range of input intensity of the signal light by using a simple configuration, an optical receiver includes local light oscillation unit for generating a local oscillation light with a constant intensity, light mixing unit for mixing the local oscillation light and a first signal light and outputting the mixed light as a second signal light, light receiving unit for converting the second signal light into an electrical signal and outputting the electrical signal as a first electrical signal, amplifying unit for amplifying the first electrical signal with a predeteiniined gain and outputting the amplified signal as a second electrical signal, and a signal processing circuit for processing the second electrical signal, wherein the gain is set so that the amplitude of the second electrical signal may be within an allowable input amplitude range of the signal processing circuit.

Abstract: A method of converting an optical communications signal having a differentially encoded multilevel modulation format into communications traffic bits, the multilevel modulation format having a plurality of constellation points, the method comprising: receiving a consecutive pair of symbol signals of said optical communications signal, the pair of symbol signals being arranged to differentially encode a plurality of communications traffic bits; and generating a plurality of optical binary signals in dependence on the symbol signals, each optical binary signal having a respective binary signal level, wherein the optical binary signals form optical versions of the encoded communications traffic bits.

Abstract: Provided is a pulse receiver capable of receiving a burst signal and decoding the burst signal with a bit error rate reduced to a target value or less by controlling a determination threshold such that decoding success rate is equal to or less than a predetermined value. A decode unit 140 decodes a pulse train 20 to information 30, counts the number of decoding successes for a predetermined time period and outputs the counted number (decoding success rate DR) to a control unit 150. The control unit 150 uses as a basis the decoding success rate DR communicated from the decode unit 140 to control the set value of reference voltage Vth used in the comparator 130.

Abstract: To stabilize power to an optical multimode receiver a multimode variable optical attenuator is connected to the receiver with the attenuator's voltage being controlled using a feedback signal provided by an output detector, the signal being processed using a control algorithm based on proportional-integrate-differential theory.

Abstract: An optical transport system in which (i) an optical transmitter is configured to adaptively change an operative constellation to use a constellation that provides optimal performance characteristics for the present optical-link conditions and/or (ii) an optical receiver is configured to change shapes of the decision regions corresponding to an operative constellation to adapt them to the type of signal distortions experienced by a transmitted optical signal in the optical link between the transmitter and receiver. Under some optical-link conditions, the optical receiver might use a decision-region configuration in which a decision region corresponding to a first constellation point includes an area that is closer in distance to a different second constellation point than to the first constellation point.

Abstract: A system may include one or more devices that may be used to simultaneously measure and modulate phases of a many-channel optical system relative to a high frequency optical carrier. This device may be constructed using analog-to-digital converters, comparators, and distributed timers. A digital processor may be used to recover phase information from the measurements and to calculate an error compared to desired phase. The processor may then apply feedback to a phase modulator to correct the phase.

Abstract: A receiver chip, system and method for on-chip multi-node visible light communication, the receiver chip comprising: an array of receiver cells comprising an array of photodetectors, each receiver cell comprises at least one photodetector and is to receive light through the at least one photodetector, and a logical layer for independently configuring at least one selected receiver cell as a communication receiving channel. The system comprises an array of receiver cells comprising an array of photodetectors, each receiver cell includes at least one photodetector and is to receive light through the at least one photodetector, a logical layer to independently configure at least one selected receiver cell as a communication receiving channel, and a processor to receive data from the logical layer and control the logical layer for configuration of the receiver cells.

Abstract: Methods, systems, and devices are described for a digital demodulator device for processing received optical signals. The device may include a quadrature error filter that receives a digitized version of an optical signal, and removes quadrature errors to generate a filtered series of data samples. The device may also include a frequency offset removal module for performing frequency rotation on the filtered series of data samples. The device may include a chromatic dispersion compensation module which removes chromatic dispersion from horizontal and vertical polarization channels. The device may include a polarization mode dispersion (PMD)/polarization dependent loss (PDL) compensation module which compensates for interference caused by PMD and PDL. The device may also include a phase recovery module configured to track and correct phase.

Abstract: A photon detection system including a photon detector configured to detect single photons, a signal divider to divide the output signal of the photon detector into a first part and a second part, wherein the first part is substantially identical to the second part, a delay mechanism to delay the second part with respect to the first part, and a combiner to combine the first and delayed second parts of the signal such that the delayed second part is used to cancel periodic variations in the first part of the output signal.

Abstract: A miniature pluggable video module having a length less than one inch, and a width less than three quarters of an inch, and a plurality of pin connectors attached to the back of the housing. The pluggable video module can be mounted horizontally or vertically. Inputs and outputs of the module can be adapted to include various types of optical or electrical connectors. The inputs and outputs of the module can be modified into various combinations of optical or electrical configurations, and the combinations of inputs and outputs also can be modified.

Abstract: Carrier phase estimation techniques are provided for processing a received optical signal having a carrier modulated according to a modulation scheme. First and second carrier phase estimation operations are performed on a digital signal derived from an optical carrier obtained from the received optical signal using coherent optical reception. The first carrier phase estimation operation tracks relatively fast phase variations of the optical carrier of the received optical signal to produce a first carrier phase estimation and the second carrier phase estimation operation tracks relatively slow phase variations of the optical carrier of the received optical signal to produce a second carrier phase estimation. A difference between the first and second carrier phase estimations is computed. Occurrence of a cycle slip is determined when the difference is greater than a threshold. A correction is applied to the first carrier phase estimation when the low pass filtered difference exceeds the threshold.

Abstract: An optical receiver includes a splitter that splits a local oscillator lightwave into a first local oscillator lightwave and a second local oscillator lightwave; a measurement unit that measures phase variation of the first local oscillator lightwave; a receiving unit that receives a signal lightwave and the second local oscillator lightwave and mixes these lightwaves and converts the mixed lightwaves into digital signal; a dispersion compensator that reduces chromatic dispersion of the digital signal; a phase processing unit that rotates phase of the dispersion-reduced signal based on the phase variation; and a discriminating unit that discriminates the phase-rotated signal.

Abstract: Compensation for in-phase (I) and quadrature (Q) timing skew and offset in an optical signal may be achieved based on the correlation between derivatives of I and Q samples in the optical signal. The magnitude of the correlation between derivatives is measured to determine the presence of skew. Correlation between derivatives may be coupled with frequency offset information and/or with trials having additional positive and negative skew to determine presence of skew. Correlations are determined according to pre-defined time periods to provide for continued tracking and compensation for timing skew that may result from, for example, thermal drift.

Abstract: An optical receiver, within a first device, may receive first configuration information from an optical transmitter, also within the first device. While receiving the first configuration information, the optical receiver may operate according to a clock. Later, the optical receiver may receive optical data from a second device according to the first configuration. While receiving the optical data from the second device, the optical receiver does not operate according to the clock, wherein the optical receiver not operating according to the clock allows the optical receiver to receive the optical data with greater sensitivity.

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 of which are encoded through a frequency-shift keyed (FSK) format and the rest of which are encoded through an additional modulation format on at least one FSK carrier. The receiver detects the signal through a dual-polarization coherent receiver front-end, and recovers polarization components of the signal by decoding a first non-zero portion of a plurality of bits carried by a symbol based on frequency slot position of at least one FSK carrier 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 FSK carrier in the polarization components. Pilot-assisted orthogonal frequency-division de-multiplexing (PA-OFDM) may be used for spectrally-efficient signal reception, even in the presence of severe FSK errors.

Abstract: A communications device includes a transmitter device having first and second optical sources and generating respective first and second modulated optical carrier signals at first and second optical carrier frequencies based upon an input signal. The communications device also includes an optical waveguide coupled to the transmitter device, and a receiver device coupled to the optical waveguide and including an FM-PM discriminator having a transfer function with a positive slope portion and a negative slope portion so that the first optical carrier frequency is positioned on the positive slope portion and the second optical carrier frequency is positioned on the negative slope portion.

Abstract: A circuit, optical transceiver and/or methods for using the same may be useful for determining average power, extinction ratio, and/or modulation amplitude when monitoring an optical transceiver and/or optical network. The circuit generally comprises a photodiode configured to generate a first current responsive to an optical signal, a current mirror coupled to a first terminal of the photodiode, and a detector coupled to a second terminal of the photodiode. The current mirror is configured to produce a second current equal to or proportional to the first current, and the detector is configured to determine a power or amplitude of the optical signal. Further, the present scheme may communicate information using a low speed signal superimposed on or combined with the relatively high speed optical signal.

Abstract: A photon detection system is provided comprising a photon detector, configured to detect photons during intervals when in a receiving state and to output a signal when a photon is received, a controller, configured to generate a time varying gating signal wherein said gating signal switches said detector between the receiving state and a non-receiving state, said controller being configured to receive and process information relating to the times photons are expected to arrive at said detector, the controller being configured to generate the gating signal such that the photon detector is in the receiving state for intervals when photons are expected and also in the receiving state for additional intervals between the intervals when the photons are expected; a detection module, configured to distinguish between when the output signal from the photon detector corresponds to an interval when photons are expected and said additional intervals.

Abstract: An optical field receiver comprises an optical branching circuit for branching a received optical multilevel signal into first and second optical signals, a first optical delayed demodulator for performing delayed demodulation on the first optical signal at a delay time T (T=symbol time), a second optical delayed demodulator for performing delayed demodulation on the second optical signal at the delay time T with an optical phase difference deviating from the first optical delayed demodulator by 90°, first and second optical receivers for converting each of the delayed demodulation signals representing x and y components of complex signals output from the first and second delayed demodulators into first and second electrical signals, and a field processing unit fort generating a first reconstructed signal representing an inter-symbol phase difference or a phase angle of a received symbol from the first and second electrical signals for each symbol time T.

Abstract: A substantially 400 Gb/s optical transceiver includes a substantially 400 Gb/s optical transmitter which includes a set of four substantially 100 Gb/s tunable optical transmitters, each transmitting a substantially 100 Gb/s optical signal in a wavelength division multiplexed form over four channel wavelengths selected such that the resulting 16 channel wavelengths are different from each other and are suitable for WDM, and an optical transmission interface including a set of four 1:4 wavelength division demultiplexers which are operative to demultiplex the substantially 100 Gb/s optical signals to produce substantially 25 Gb/s optical signals over each of the 16 different channel wavelengths, and a 16:1 wavelength division multiplexer which is operative to multiplex the substantially 25 Gb/s optical signals of the 16 different channel wavelengths to generate a substantially 400 Gb/s optical signal.

Abstract: A digital coherent receiver includes a sampling phase detector to detect a phase of a sampled digital signal, and a phase adjustor to adjust the sampling phase of the digital signal based upon the detected phase. The phase detector includes filters to equalize the digital signal with different equalization characteristics; sensitivity monitoring phase detectors, each connected to one of the filters and outputting a phase detection signal representing the phase of the output signal from the associated filter together with a sensitivity monitoring signal representing the sensitivity of the phase detection; sensitivity correction coefficient generators, each generating a sensitivity correction coefficient for correcting the associated phase detection signal using a square sum of the sensitivity monitoring signals; and an adder to add the phase detection signals that have been corrected by the sensitivity correction coefficients, and output a phase signal.

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: Systems and methods for determining the envelope of a modulated signal using high bandwidth and low bandwidth samples of a hybrid signal. The hybrid signal is obtained by mixing the modulated signal with its carrier signal. The systems and methods of the present disclosure may be suitable for equivalent-time or real-time oscilloscopes.

Abstract: Data for transmission by an optical transmitter that is driven by a signal driver is encoded, where the encoding is according to a criterion that specifies a reduction of an aggregate electrical current of the signal driver.

Abstract: An electro-optical device includes an optical de-multiplexing portion operative to output a first optical signal having a first wavelength and a second optical signal having a second wavelength, an array of photodetectors, and a switching logic portion communicatively connected to the array of photodetectors, the switching logic portion operative to determine which photodetector of the array of photodetectors is converting the first optical signal into a first electrical signal and output the first electrical signal from a first output node associated with the first optical signal.

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 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: 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: A polarization-insensitive optical receiver for demodulating a phase-modulated input optical signal is provided. The optical receiver includes successively a polarization splitter, a first and second interferometric modules including respective delay lines, and a plurality of detectors. The input optical signal is split into two substantially orthogonally-polarized components, which are launched along respective optical paths into the corresponding interferometric modules where they demodulated and subsequently recombined prior to being detected by the plurality of detectors. Advantageously, the optical receiver allows mitigating undesired discrepancies between the optical paths traveled by the two polarization components by arranging the respective delay lines of the interferometric modules into intertwined spiraling structures.

Abstract: Analog transport of a wideband RF signal is effectively and efficiently provided using a coherent, narrowband optical carrier. The wideband RF signal is phase modulated onto the carrier at a first location. Non-coherent discrimination is applied to the modulated carrier at a second, different location to generate an amplitude modulated optical signal where the amplitude modulation represents the original wideband RF signal. A photo-detector is then used to regenerate a representation of the original wideband RF signal. The method and apparatus of the invention can be applied in systems dedicated to the analog RF transport or in wavelength division multiplexed systems which also provide transport for other analog or digital data.

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: A signal level detect circuit configured to assess an input signal with varying amplitude signal levels and to generate an indicator signal includes an input circuit configured to receive the input signal and to process the input signal, the input circuit including a first node on which the input signal is sampled; a comparator configured to compare the processed input signal to a signal level threshold and generate a comparator output signal; and an active discharge circuit configured to provide a first discharge current to the first node in response to the comparator output signal. The comparator output signal changes from a low output state to a high output state in response to the comparator input signal, and the active discharge circuit generates the first discharge current to discharge the sampled input signal on the first node after the comparator output signal changes to the high output state.

Abstract: An optical signal demodulator includes: an obtaining unit configured to obtain a spectrum of an optical signal generated by a second signal being superimposed on a first signal using frequency modulation; an identifying unit configured to identify a peak wavelength which is a wavelength corresponding to a peak position of the spectrum; and a demodulating unit configured to demodulate the second signal from the optical signal using a wavelength-variable filter to which a transmitted wavelength band has been set based on the peak wavelength.

Abstract: An apparatus comprising a frequency-domain equalizer that has been iteratively generated to compensate for filtering effects of a wavelength selective switch, wherein the FDEQ is configured to process in a frequency domain digital samples of a polarization multiplexed phase-shift-keying signal that has been transported over an optical channel.

Abstract: A receiver or spectrum determiner includes stages, Fourier transforms, phase delays and a summer. The stages are coupled are in pipelined fashion along a signal path. Each of the stages has a respective output for providing at least one respective demodulated signal for the stage. The Fourier transforms are for receiving the respective demodulated signal and providing a respective Fourier transform. The phase delays each have a delay associated with the respective stage. Each phase delay is for receiving the respective Fourier transform and providing a respective phase delayed transform in accordance with the respective stage. The summer is for summing the respective phase delayed Fourier transform from each phase delay. The receiver can be an electronic intelligence (ELINT) receiver.

Abstract: To reduce PAPR in an optical OFDM communication system, light is phase-modulated by a base-band OFDM signal which is the output of a transmission signal processing unit 100 provided in an inner section of an optical receiver. When optical communication is implemented with the light as signal light, PAPR of low level of almost 0 dB can be achieved at places in an inner section of an optical fiber wherein the optical power is large. The signal light is propagated along an optical fiber which is a transmission path, the light is passed through a delay interferometer, and converted to electrical signals by two optical receivers. Each of the two electrical signals is converted to a subcarrier by FFT signal processing and an AD converter disposed in an inner section of the optical receivers, then, subcarriers having the same frequency are subtracted and decoded, and data is regenerated.

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.