Abstract: A node can include a clock; and mapper circuitry configured to determine a timestamp from the clock, and transmit the timestamp to a second node in a Radio over Ethernet (RoE) frame with the timestamp in a control subtype and with an operational code (opcode) that designates the timestamp is in the frame. The node can also include a demapper circuit configured to receive a second timestamp from the second node in a second RoE frame, and provide the second timestamp to a Differential Clock Recovery (DCR) circuit for adjustment of the clock to a second clock at the second node.

Abstract: A local device of a time synchronization system includes a path switching unit that connects respective remote devices using individual optical fibers and switches the respective optical fibers sequentially in a cyclic order, a counter unit, a phase difference memory unit, and a table unit. The counter unit counts a pulse signal P1d demodulated by a PPS demodulation unit to obtain a count value. The phase difference memory unit stores the count value as path information in association with a phase difference detected by a phase detection unit, and outputs the phase difference associated with this path information indicated by the count value to the variable delay unit. When the count value is input, the table unit outputs a path switching signal for switching to the next optical fiber in the cyclic order to the path switching unit and the path switching unit performs switching to the next optical fiber.

Abstract: In general, various aspects of the techniques described in this disclosure provide time synchronization for encrypted traffic in a computer network. In one example, the disclosure describes an apparatus, such as a network device, having a control unit for a network device in a computerized network having a topology of network devices; and a forwarding unit operative to determine a release time for sending a synchronization packet in accordance with a time synchronization protocol; modify the synchronization packet to include a release timestamp specifying the release time; sending a time value via sideband data associated with the synchronization packet, wherein the time value is based on the release time specified by the release timestamp; and schedule transmission of the synchronization packet for a time corresponding to the time value in the sideband data, the synchronization packet to be transmitted to a destination network device.

Abstract: Disclosed in some examples, are optical devices, systems, and machine-readable mediums that send and receive multiple streams of data across a same optical communication path (e.g., a same fiber optic fiber) with a same wavelength using different light sources transmitting at different power levels—thereby increasing the bandwidth of each optical communication path. Each light source corresponding to each stream transmits at a same frequency and on the same optical communication path using a different power level. The receiver differentiates the data for each stream by applying one or more detection models to the photon counts observed at the receiver to determine likely bit assignments for each stream.

Abstract: A method of combining optical signals from a plurality of optical fibers into a single optical signal includes receiving, at corresponding optical-signal receivers optically coupled to corresponding trunk fibers, respective optical signals. The method further includes determining, by the corresponding optical-signal receivers, when each respective optical signal is received. When the respective optical signal is received, the method includes performing the following steps: converting, by the corresponding optical-signal receiver, the respective optical signal to a corresponding electrical signal; transmitting, by the corresponding optical-signal receiver, the corresponding electrical signal to a corresponding input channel of an electrical-multiplexing device; and configuring the electrical-multiplexing device to select the corresponding input channel.

Abstract: A method of measuring lengths of optical fibers on forward and return paths is provided in order to synchronize clocks of optical nodes connected by asymmetrical optical fiber paths. The method includes calculating, by a first optical network device, a first propagation delay of a first optical signal transmitted at a first wavelength on a first optical fiber to the first optical network device from a second optical network device and a second propagation delay of a second optical signal transmitted at a second wavelength on the first optical fiber to the first optical network device from the second optical network device. The second wavelength is different from the first wavelength. The method further includes determining, by the first optical network device, a first length of the first optical fiber based on the first propagation delay and the second propagation delay.

Abstract: A method for removing static differential delays resulting from an independent transport of the client signals of a client signal bundle through an optical transport network, OTN, which comprises OTN mappers mapping received client signals to ODU signals transported to OTN demappers demapping received ODU signals to client signals, wherein a process slave, PS, at the OTN mapper end of said OTN network supplies continuously or in response to a received request information about timing relations between the client signals of said client signal bundle to a process master, PM, at the OTN demapper end of said OTN network used by the process master, PM, to remove the static differential delays between the client signals of the respective client signal bundle.

Abstract: A parallel-processing apparatus has information-processing apparatuses coupled mutually through an optical transmission line having channels. Each of the information-processing apparatuses has processors allocated to the channels of the optical transmission line, a controller and a display. When one of the processors detects a channel failure, the processor notifies a processor in the other information-processing apparatus of the channel failure, notifies the controller of the information-processing apparatus of the channel failure and notifies the controller of the information-processing apparatus of the notification of the channel failure from the other information-processing apparatus.

Abstract: Embodiments for accurately performing time of flight estimations are provided. These embodiments include using a first wireless device to monitor a wireless link and subsequently generate a wireless link estimation based on the monitoring. The embodiments also include deriving a correction metric based on the generated wireless link estimation and transmitting the correction metric from the first wireless device to a second wireless device. The second wireless device may then calculate a time of arrival of a first signal received from the first wireless communication device and correct any errors associated with the time of arrival calculation using the received correction metric. Further, the second wireless device may transmit the corrected time of arrival back to the first wireless device, such that the first wireless device can use the corrected time of arrival to estimate the time of flight of the first signal.

Abstract: According to an embodiment, a transmission device is for a second quantum communication system sharing a quantum communication channel with a first quantum communication system, and includes a generator, a modulator, a controller, and a changer. The generator is configured to generate a photon. The modulator is configured to transmit a quantum signal generated by modulating the photon to a reception device. The controller is configured to control the generator and the modulator. The changer is configured to input, to the controller, control signals for changing an operation timing of the generator and an operation timing of the modulator when an error rate of the quantum signal of the first quantum communication system and an error rate of the quantum signal of the second quantum communication system are equal to or higher than a predetermined threshold.

Abstract: A correlation processor derives a correlation value indicating correlation between each of a plurality of reference signals produced by extracting symbols from the synchronization signal of each pattern at a predetermined interval and a received signal. A controller compares the correlation value for each pattern and for each sample derived by the correlation processor with a threshold value and, when at least one correlation value is larger than the threshold value, changes symbols extracted to produce respective reference signals before causing the correlation processor to perform the same process, incorporating the received signal newly acquired. A first selector selects one of the plurality of patterns when all symbols of the synchronization signal have been extracted to produce the reference signals and at least one correlation value is larger than the threshold value.

Abstract: Provided are an optical transceiver, an optical transmitter IC, and an optical receiver IC, which can be applied to both a case of coding an optical signal and a case of decoding an optical signal, and can suppress an influence of waveform degradation with an inexpensive circuit. The optical transceiver includes an optical transmitter, an optical receiver, and at least any one of: a first delay circuit included in the optical transmitter and configured to delay an input first multi-level digital signal by a delay time corresponding to an amplitude level of the first multi-level digital signal; and a second delay circuit included in the optical receiver and configured to delay an input second multi-level digital signal by a delay time corresponding to an amplitude level of the second multi-level digital signal.

Abstract: An optical line terminal (OLT) coupled to a plurality of optical network units (ONUs) through a passive optical network (PON). The OLT includes a transceiver configured to communicate via a management channel of a communication network with a plurality of OLTs. The communication includes sending or receiving a notification, wherein the notification includes the following: a source OLT identifier associated with a source OLT sending the notification, wherein the source OLT is configured to communicate over a first channel at a first wavelength of the PON; a destination OLT identifier associated with a destination OLT receiving the notification, wherein the destination OLT is configured to communicate over a second channel at a second wavelength of the PON; and an ONU identifier associated with a first ONU associated with the notification.

Abstract: An optical modulator comprises a silicon substrate, a buried oxide (BOX) layer disposed on top of the silicon substrate, and a ridge waveguide disposed on top of the BOX layer and comprising a first n-type silicon (n-Si) slab, a first gate oxide layer coupled to the first n-Si slab, a first p-type silicon (p-Si) slab coupled to the first gate oxide layer, and a light propagation path that travels sequentially through the first n-Si slab, the first gate oxide layer, and the first p-Si slab.

Abstract: A method for performing code block segmentation for wireless transmission using concatenated forward error correction encoding includes receiving a transport block of data for transmission having a transport block size, along with one or more parameters that define a target code rate. A number N of inner code blocks needed to transmit the transport block is determined. A number M—outer code blocks may be calculated based on the number of inner code blocks and on encoding parameters for the outer code blocks. The transport block may then be segmented and encoded according to the calculated encoding parameters.

Abstract: A device and method for collecting data from an event and retransmitting same with high value portions of the data identified. Low value portions of the data from the event are identified so, if desired, they may be removed and replaced by other data, such as stats from the event, stats from other events, and trivia relevant to the event. Indications alert end users that the data signal is returning to high value portions.

Abstract: In one example implementation according to aspects of the present disclosure, a method may include detecting, by a computing system, a touch input on the computing system by analyzing a change in a data stream from a sensor of the computing system by applying a first signal de-noising algorithm to the data stream. The method may further include determining, by the computing system, the nature of the detected touch input. Additionally, the method may include generating, by the computing system, a discrete cursor movement from a set of discrete cursor movements based on the determined nature of the detected touch input.

Abstract: A method of tracking repeated performance problems in a machine is disclosed. The method comprises storing the faults in a computer memory, and assigning a classification value to the machine based on the frequency and number of the faults. Based on the classification value of the cash handing device it is determined whether the cash handing device needs to be serviced. The faults can be related to one of the hardware, the cash reject rate, image handling, crash rate, user claim rate, and check handling accuracy of the machine.

Abstract: A method of tracking repeated performance problems in a machine is disclosed. The method comprises storing the faults in a computer memory, and assigning a classification value to the machine based on the frequency and number of the faults. Based on the classification value of the cash handing device it is determined whether the cash handing device needs to be serviced. The faults can be related to one of the hardware, the cash reject rate, image handling, crash rate, user claim rate, and check handling accuracy of the machine.

Abstract: The present disclosure describes a wired communication device having media access control (MAC) circuitry and physical layer (PHY) circuitry. The MAC circuitry frames one or more data packets in accordance with a wired communication standard or protocol to provide one or more data frames. The one or more data frames include one or more packets that are separated by interpacket gaps (IPGs). The MAC circuitry selectively choses a duration of the IPGs to maintain an average IPG duration. The PHY circuitry encodes the one or more data frames in accordance with a line coding scheme that is efficiently represents different possible combinations for types of characters present in the one or more data frames.

Abstract: One example discloses an optical communication interface for a handheld device: wherein the handheld device, has an external surface; wherein the external surface includes an interior facing side and an exterior facing side; a first optical receiver, on the interior facing side of the handheld device, having an optical input and an electrical output; wherein the electrical output is coupled to circuitry; and wherein the optical input is configured to be optically coupled to a second optical transmitter on the exterior facing side of the handheld device.

Abstract: Methods, systems, and devices are disclosed for using optical modes in optical waveguides to carry different optical communication signals. In one aspect, an optical device for optical MDM in optical communications includes an optical waveguide configured to support multiple optical waveguide modes and to carry light of different optical communication channels in different optical waveguide modes, respectively, of the multiple optical waveguide modes. The optical device includes an optical resonator configured to be capable of carrying an optical communication channel in one optical resonator mode and optically coupled to the optical waveguide to selectively couple the optical communication channel in the optical resonator into the optical waveguide to add a channel into the optical waveguide via optical mode division multiplexing. In another aspect, an optical mode division demultiplexing can be performed by coupling an optical waveguide and an optical resonator.

Abstract: An optical level control apparatus includes an input port, an output port, an optical device to assume a state of outputting light inputted to the input port from the output port and a state of not outputting the light inputted to the input port from the output port; a detector to detect an intensity of the light inputted to the input port, and a control unit to detect an input of an optical burst signal to the input port on the basis of a result of detecting the intensity of the light and to control the optical device so that the signal, in which to eliminate a field extending up to an elapse of a period of first time equal to or shorter than laser ON time period of the signal from a head of the signal with its input being detected, is output from the output port.

Abstract: In an optical fiber network for transmitting optical signals in a robot having three or more joints connecting a plurality of links in series such that the links include two end links located at either end and intermediate links provided between the two end links, and the links connected by the joints are moveable relative to each other, a plurality of optical transceiver modules are provided on the links such that at least one optical transceiver module is provided on each link; and a plurality of optical fiber cables connect the optical transceiver modules in a ring; wherein at least one end of each optical fiber cable connecting the optical transceiver modules provided on different links is connected to one of the optical transceiver modules provided on the intermediate links.

Abstract: An OLT (1) is formed by N optical transceivers (11), one PON control circuit (12), and one selection and distribution circuit (13). An optical transceiver selection control signal (SC) is transferred from the PON control circuit (12) to the selection and distribution circuit (13). The optical transceiver selection control signal (SC) indicates the timing of a discovery window, the timing of a grant, and a logical link identification number of a registered ONU assigned to the grant (a logical link identification number for a logical link with the registered ONU). The selection and distribution circuit (13) selects one optical transceiver (11-s (s is an integer falling within a range of 0 to N?1)) from the optical transceivers (11-0 to 11-N?1) based on the optical transceiver selection control signal (SC) from the PON control circuit (12).

Abstract: A method of providing data using visible light communication (VLC) and a VLC system therefor is provided, the method for easy utilization, in a user terminal, of information provided by a lighting apparatus based on a position at which the lighting apparatus is provided.

Abstract: A method distributes clock synchronization information within an optical communications network that includes a plurality of network elements. The method receives an ingress clock synchronization message at a first network element. The ingress clock synchronization message includes a clock synchronization message identifier and a correction field. The clock synchronization message identifier is inserted into an optical channel frame overhead and the ingress clock synchronization message is inserted into an optical channel frame payload. The optical channel frame overhead and the optical channel frame payload are transmitted across the first network element, across the network to a second network element, and across the second network element. A transit time of the clock synchronization message identifier is determined across each of the network elements.

Abstract: A high-speed multi-channel data transmission method is disclosed. The method includes that: a data sender replaces data at intervals of N periods with frame headers in data channels, sequentially stores the data replaced with the frame headers in the data channels in a Deskew channel, and sends the data in the data channels and data in the Deskew channel to a data receiver; the data receiver determines frame header locations of the data channels and the Deskew channel, calculates offsets of the data channels according to the frame header locations, and performs period compensation for the data channels according to the calculated offsets to keep the frame header of each data channel and the frame header of the Deskew channel in a relative relationship the same as that at the data sender; and the frame headers on the data channels and the corresponding data on the Deskew channel are replaced to finish data restoration.

Abstract: A method distributes clock synchronization information within an optical communications network having a plurality of network elements. The method receives an ingress clock synchronization message at a first network element. The ingress clock synchronization message includes a clock synchronization message identifier and a correction field. The clock synchronization message identifier is inserted into an optical channel frame overhead and the ingress clock synchronization message is inserted into an optical channel frame payload. The optical channel frame overhead and the optical channel frame payload are transmitted across the first network element, across the network to a second network element, and across the second network element. A transit time of the clock synchronization message identifier is determined across each of the network elements.

Abstract: The disclosure concerns quantum repeater network system that does not need any matter qubit. According to the quantum repeater network system for performing quantum communication between one transmitter/receiver and the other transmitter/receiver via transmission repeaters and reception repeaters, each of the transmission repeaters prepares quantum systems in an irreducibly entangled state, each of the quantum systems being associated with a reception repeater as a transmission destination, and transmits, to the associated reception repeater, each of the quantum systems in the irreducibly entangled state together with a quantum system entangled with the quantum system.

Abstract: An information communication method of transmitting a signal using a change in luminance is provided. The information communication method includes: determining a pattern of the change in luminance, by modulating the signal to be transmitted; and transmitting the signal, by at least one light emitter changing in luminance according to the determined pattern of the change in luminance. In the determining, a first luminance change pattern corresponding to a body, a second luminance change pattern indicating a header for specifying the body, and a third luminance change pattern indicating another header different from the header are determined. In the transmitting, the header, the body and the other header are transmitted by the at least one light emitter changing in luminance according to the first luminance change pattern, the second luminance change pattern, the first luminance change pattern and the first luminance change pattern in the stated order.

Abstract: A method and apparatus for time synchronization between a plurality of nodes in a network. The apparatus distinguishes between an optical synchronization signal for synchronization between nodes and an optical data signal for data transmission, and synchronizes nodes with each other using the optical synchronization signal.

Abstract: An information communication method of transmitting a signal using a change in luminance is provided. The information communication method includes: determining a pattern of the change in luminance, by modulating the signal to be transmitted; and transmitting the signal, by at least one light emitter changing in luminance according to the determined pattern of the change in luminance. In the determining, a first luminance change pattern corresponding to a body which is a part of the signal and a second luminance change pattern indicating a header for specifying the body are determined. In the transmitting, the header and the body are transmitted by the at least one light emitter changing in luminance according to the first luminance change pattern, the second luminance change pattern, and the first luminance change pattern in the stated order.

Abstract: An apparatus and method for scalable frame alignment in a high data-rate communications system. OTUk/ODUk frame alignment uses serial processing of a match vector, or serial processing of received OTUk/ODUk bytes to reduce the footprint occupied by the processing logic.

Abstract: There is provided a communication control device including a communication control processing portion that performs at least one type of communication control processing when a control signal that requests a response signal is received from a partner device, a transmission processing portion that transmits the response signal to the partner device after the processing that the communication control processing portion performs when the control signal is received from the partner device, a processing time measurement portion that measures time that is consumed by the processing by the communication control processing portion, and a processing content setting portion that, based on the measured processing time that has been measured by the processing time measurement portion and on a response processing time for the response to the control signal, sets content of processing that the communication control processing portion will be made to perform within the response processing time.

Abstract: An apparatus includes a bank of optical detectors, an input optical filter and a selector. The optical detectors are configured to output respective detection indications in response to detecting a presence of an optical signal. The input optical filter is configured to receive an input optical signal having an input wavelength, and to route the input optical signal to one of the optical detectors in the bank depending on the input wavelength. The selector is configured to select an output wavelength based on the detection indications of the optical detectors, and to cause generation and transmission of an output optical signal at the selected output wavelength.

Abstract: A method and apparatus are provided for presenting multimedia content to a caller and/or a called party in association with a telephone call. Content may be presented pre-ring (before the called party's telephone rings), in-call, and/or post-call. Content presented to a party may be related to another party participating in the call or may be related to a third party (e.g., an advertiser that paid for the ability to have its content presented). Presented content may be actuable, to allow a caller to change the destination of a call, take advantage of an offer presented to him or her, redeem a coupon, schedule or queue a subsequent call, etc. To find a desired destination party, a caller may initiate a manual or automatic search of his or her local contacts (on his telephone) and/or a central or global directory or contact list.

Abstract: The present invention discloses a clock recovery circuit, an optical receiver, and a passive optical network device. In the clock recovery circuit provided by the embodiment of the present invention, a first signal indicating whether a data loss abnormality occurs in initial serial data is introduced at a side of a phase detector, and a phase adjustment control signal is output to a phase adjustor according to a state of the first signal; and the phase adjustor performs different types of phase adjustment according to a state of the initial serial data, so that a data sampler can recover an accurate clock when the initial serial data is normal and can implement smooth switching of output clock information in special cases such as initial serial data clock loss or recovery, and no great abrupt phase change occurs, thereby ensuring stable and reliable working of a system.

Abstract: The display device according to the present invention comprises a substrate and at least one optical coupler having an optical receiver and an optical transmitter formed on the substrate, wherein the optical transmitter transmits an optical signal to the optical receiver.

Abstract: Methods, systems, and devices are described for detecting and correcting a cycle slip occurrence in a coherent receiver. Unique words are used in each received frame to detect phase changes that indicate the occurrence of a cycle slip within a frame. The location of the cycle slip is identified based on measurements made within the frame. Those measurements include phase estimation measurements and reliability measurements. A phase of a portion of the frame subsequent to the identified location of the cycle slip is adjusted to correct for the cycle slip. By combining phase estimates of symbols from both vertical and horizontal polarizations, the location of the cycle slip may be more accurately determined because the measurement windows is less susceptible to thermal noise. The phase estimates are combined by adjusting a phase of the symbols of one polarization to match a phase of the symbols of the other polarization.

Abstract: The present invention relates to the Passive Optical Network (PON) technology, and a method for sending an upstream transfer frame in a PON is provided. The method includes: after success of link, sending a preamble according to an allocated time slot, sending a burst synchronization delimiter, and then sending successively a burst header, a Gigabit-Capable Passive Optical Network (GPON) Transmission Convergence (GTC) frame header, and GTC frame data. In the sent synchronization delimiter, the number of zeros on the odd bits is N, the number of non-zeros on the odd bits is M, a relation |N?M|?1 is satisfied, the max number of zeros in a continuous zero group is X, the max number of non-zeros in a continuous nonzero group is Y, and a relation |X?Y|?1 is satisfied. A device for sending an upstream transfer frame in a passive optical network is further provided.

Abstract: In the present invention, wasted power consumption caused when a clock and data recovery unit in an optical network unit in a PON system is activated from a power-saving state is reduced and rapid, secure communication is performed. A clock and data recovery unit includes a phase-locked loop that can be set to normal mode or power-saving mode and that includes a voltage-controlled oscillator and recovers a clock signal and a data signal from input signals. The clock and data recovery unit includes a reference clock multiplier circuit that multiplies a reference clock signal and outputs the multiplied reference clock signal; and a frequency training loop that includes the same voltage-controlled oscillator and performs synchronous oscillation training by the voltage-controlled oscillator using the reference clock multiplier circuit before the phase-locked loop transitions from power-saving mode to normal mode.

Abstract: A method distributes clock synchronization information within an optical communications network having a plurality of network elements. The method receives an ingress clock synchronization message at a first said network element. The ingress clock synchronization message includes a clock synchronisation message identifier and a correction field. The clock synchronisation message identifier is inserted into an optical channel frame overhead and the ingress clock synchronisation message is inserted into an optical channel frame payload. The optical channel frame overhead and the optical channel frame payload are transmitted across the first network element, across the network to a second said network element, and across the second network element. A transit time of the clock synchronisation message identifier is determined across each of the network elements.

Abstract: A method and apparatus for time synchronization between a plurality of nodes in a network. The apparatus distinguishes between an optical synchronization signal for synchronization between nodes and an optical data signal for data transmission, and synchronizes nodes with each other using the optical synchronization signal.

Abstract: A transmitter and a receiver for an optical telecommunication system of the WDM type are disclosed. In one aspect, the transmitter uses a chromato-temporal encoder which, with each block of symbols to be transmitted, associates a code matrix, where each element of the matrix corresponds to a wavelength and a use of the channel. The transmitter includes multiple modulators, where each modulator modulates a laser beam at a wavelength during a use of the channel by an element corresponding to the code matrix. The beams modulated in this manner are multiplexed in an optical fiber. Another embodiment using both a wavelength and a polarization encoding is also proposed.

Abstract: A transmission apparatus includes: a plurality of logical lanes; a receiver configured to receive a signal including synchronization information of a frame; a distributor configured to divide data included in the received signal into frame elements and cause the plurality of logical lanes to store the data; and a transmitter configured to transmit the data stored in the logical lanes to lines corresponding to the logical lanes. When the data is stored in the plurality of logical lanes, the distributor groups the logical lanes into a plurality of groups and associates the frame elements with the synchronization information.

Abstract: An Ethernet adapter system may include a transmitter to insert a payload type identifier sequence in a generic frame procedure header to indicate that a network is a converged enhanced Ethernet network. The transmitter may insert idle sequences in a stream of data frames transmitted along a link. The system may include a receiver to recognize a condition and to force a loss of synchronization condition on the link that will be converted by the receiver into a loss of light condition. The receiver may scan the transmitted stream of data frames for invalid data frames and introduce a code into the stream of data frames whenever an invalid data frame is detected.

Abstract: Disclosed are a phase locked loop (PLL) of a digital scheme and a method thereof. More specifically, disclosed are a digital phase locked loop having a time-to-digital converter (TDC), a digital loop filter (DLF), and a digitally controlled oscillator (DCO), and that is designed to have a constant jitter characteristic at all times even though an operating condition of a circuit varies according to a process, voltage, temperature (PVT) change, and a method thereof.

Abstract: An OLT that receives a signal in which transmission signals having a plurality of transmission rates are time-division multiplexed, as a received signal, and performs data reproduction by selecting reproduction data to be reproduced, among oversampled signals obtained by oversampling the received signal. The OLT includes a data-signal-information acquisition unit that acquires a transmission rate of a received signal targeted for a process of the data reproduction, a sampling frequency control unit that determines a sampling frequency to be used for the oversampling based on the transmission rate, and a sampling-clock generation unit that generates a clock signal having the sampling frequency determined by the sampling-frequency control unit, and performs the oversampling based on the clock signal.

Abstract: An optical transmission system includes at least a first optical link to transmit a first data signal as a part of a multi-lane signal and a second optical link to transmit a second data signal as another part of the multi-lane signal; on the transmission side, a reference clock is constantly applied to the first data signal of the first optical link, and a delay clock is applied to the second data signal responsive to a control signal on the second optical link; on the receiving side, the phase of a first clock signal detected from the first data signal received on the first optical link and the phase of a second clock signal detected from the second data signal received on the second optical link are compared, and the control signal is detected from the comparison result.