Abstract: It is provided an optical access system, comprising an optical line terminal which is coupled to another network and optical network units which are coupled to the optical line terminal and to a plurality of user terminals. Each of the optical network units obtains a capacity of a buffer included in the each of the optical network unit and a link speed between the each of the optical network units and one of the plurality of user terminals that is coupled to the each of the optical network units; determines a sleep time based on the obtained capacity and the obtained link speed in a case where no communication frames are transmitted for a given period of time from any one of the plurality of user terminals and the optical line terminal; and sets in a sleep state for the determined sleep time.

Abstract: In accordance with embodiments of the present disclosure, a method for compensation of noise in an optical device is provided. The method may include calculating noise present in an optical carrier signal. The method may also include generating quadrature amplitude modulation input signals, the quadrature amplitude modulation input signals each including a term for compensation of the noise based on the calculated noise. The method may further include modulating the optical carrier signal to generate a modulated optical signal based on quadrature amplitude modulation input signals.

Abstract: An optical packet switching system includes an optical packet generator for generating an optical packet signal, an optical packet switching unit, provided with an optical switch, for switching the route of an inputted optical packet signal by controlling on/off of the optical switch, and an optical signal-to-noise ratio measuring unit for measuring the optical signal-to-noise ratio of the optical packet signal outputted from the optical packet switching unit. When switching the route of the optical packet signal, the optical packet switching unit outputs an optical packet signal with optical noise by keeping the optical switch on longer than the time width of the packet signal. The optical signal-to-noise ratio measuring unit measures the optical signal power and the optical noise power, respectively, in the optical packet signal with optical noise and measures the optical signal-to-noise ratio by calculating the ratio between the optical signal power and the optical noise power.

Abstract: A method and apparatus for testing an optical coupler. Inputs of the optical coupler are connected to output ports of an optical signal source. Outputs of the optical coupler are connected to input ports of an optical signal detector system. Optical signals sent through combinations of the inputs and the outputs of the optical coupler are measured using a switching system controlled by a controller to form measurements of the optical signals.

Abstract: In a passive optical network, a downstream transmission rate from an OLT to multiple ONTs can be optimized by matching a transmission scheme for frames addressed to a channel to the downstream transmission characteristics of the channel. An FEC coding can be made channel dependent so that channels with low error rates can use minimal protection, and therefore minimal overhead, while channels with high input bit error rates can use the level of FEC coding required to produce a desired output bit error rate.

Abstract: A control device for an optical channel monitor includes: at least one of a processor and a circuit configured to stop calibration of a measured wavelength when no peak intensity of a wavelength of incoming light is detected, the optical channel monitor measuring a light intensity at the measured wavelength, the at least one of processor and circuit configured to determine presence of a peak intensity in the incoming light when detecting the incoming light with a light intensity equal to or more than a given intensity, the at least one of processor and circuit configured to permit the calibration of the measured wavelength which has been stopped to be resumed when the wavelength peak is determined to be present.

Abstract: A method of tap coefficient correction includes: obtaining a synchronization symbol difference between a first polarization and a second polarization orthogonal to the first polarization; obtaining a delay amount of each of the first polarization and the second polarization in an adaptive equalizer; calculating, in a case where a horizontal axis represents a tap number and a vertical axis represents a tap coefficient and a tap number or a nearest tap number with which an area of a drawn figure is halved is set as a gravity center of tap coefficients, a correction reference gravity center of the tap coefficients set in the adaptive equalizer, based on the synchronization symbol difference and the delay amount; and performing a correction of shifting an entire tap coefficients in units of symbol to cause the correction reference gravity center to be closest to a tap center.

Abstract: An optical communication system comprising an optical fiber connected to a first signal regeneration node located at a first end of the optical fiber and a second signal regeneration node located at a second end of the optical fiber; intermediary nodes located between the first and second signal regeneration nodes, wherein one or more pairs of adjacent intermediary nodes each define a span distance along the optical fiber; and one or more Raman amplifiers located within each span distance along the optical fiber, wherein at least one of the one or more Raman amplifiers comprises a case that encases one or more lasers and a temperature controller comprising a temperature sensor to monitor a temperature of the one or more lasers; and a temperature regulator to control a temperature of the one or more lasers.

Abstract: Provided is a method of measuring signal transmission time difference of a measuring device. The measuring device according to embodiments, by measuring a skew on two optical paths through signal delays of sufficient sizes for skew measurement on the optical paths, even a skew having a minute size can be measured within a measureable range.

Abstract: An optical transceiver and an optical network system for performing a data communication and monitoring an optical link are disclosed. The optical transceiver may simultaneously perform the data communication and monitor the optical link, and a wavelength of an optical signal for the data communication and a wavelength of an optical signal for monitoring the optical link may be differently set.

Abstract: A monitoring apparatus, that monitors a wavelength tunable optical filter for filtering an optical signal to which a frequency modulation component is added, includes: an optical filter configured to filter the optical signal output from the wavelength tunable optical filter; a detector configured to detect amplitude of the frequency modulation component included in the optical signal output from the optical filter; a generator configured to generate an output-side amplitude distribution representing a distribution of the amplitude of the frequency modulation component detected by the detector, by sweeping a transmission wavelength of the optical filter; and a monitoring unit configured to monitor arrangement of a transmission wavelength band of the wavelength tunable optical filter with respect to a spectrum of the optical signal based on the output-side amplitude distribution generated by the generator.

Abstract: There is provided a method for determining the in-band noise in agile multichannel Dense Wavelength Division Multiplexing (DWDM) optical systems, where the interchannel noise is not representative of the in-band noise in the optical channel. The method relies on the analysis of two observations of the same input optical signal. In the two observations, the linear relationship between the optical signal contribution and the optical noise contribution (e.g. the observed OSNR) is different, which allows the discrimination of the signal and noise contributions in the input optical signal. In a first approach, the two observations are provided by polarization analysis of the input optical signal. In a second, the input optical signal is obtained using two different integration widths.

Abstract: An optical communication network includes a plurality of optical transmission devices, a communication path, an optical repeater, and a supervisory controller that includes a supervisory control information sender which is installed on at least one of one of the optical transmission devices and the optical repeater and controls a drive signal supplied to a semiconductor optical amplifier that amplifies and outputs input signal light onto the communication path on the basis of the supervisory control information, and a supervisory control information receiver that receives the light which has been output from a semiconductor optical amplifier and transmitted through the communication path, converts the received light to an electric signal and identifies the supervisory control information on the basis of an intensity-modulated component of the total power of the electric signal in at least the other of one of the optical transmission devices and the optical repeater.

Abstract: A transport apparatus includes a plurality of transport processing units. The transport processing unit transports optical signals on an optical network which controls, by transmitting or receiving the optical signals including control information, apparatuses that are managed on the basis of areas. The transport processing unit includes a setting-information storage unit that stores therein setting information indicating a group to which a plurality of apparatuses within the area belongs, a frame generating unit that, upon receiving the optical signal, determines on the basis of the setting information whether the control information is to be terminated or to be passed through itself, sets a destination depending on the result of the determination, and generates a frame including the control information, and a path switching unit that switches a path of the frame on the basis of the destination of the frame.

Abstract: An optical receiver having an optical IQ modulator configured to generate an optical local-oscillator (OLO) signal for optical homodyne detection of an optical input signal applied to the optical receiver. The optical receiver further has (i) a phase detector configured to generate an electrical measure of the phase difference between the OLO signal and a carrier wave of the optical input signal and (ii) a phase-lock loop configured to drive the optical IQ modulator using the electrical measure. In an embodiment, the phase detector is configured to generate the electrical measure using both I and Q components of the homodyne-detected signal and in a manner that enables the optical receiver to be compatible with the M-QAM modulation format.

Abstract: An optical module include a first substrate including a first surface over which a light emitting element is mounted, an optical waveguide provided with a second surface of the first substrate, a mirror configured to reflect output light of the light emitting element to the optical waveguide, a second substrate, and a light receiving element configured to receive leakage light produced when the output light from the light emitting element is transmitted through the mirror disposed in the optical waveguide, the light receiving element being mounted over the second substrate different from the first substrate.

Abstract: Phase nonlinearities of an optical communications system are monitored by generating a test signal which includes a predetermined property that is uniquely associated with at least one phase nonlinearity of the optical communications system. The predetermined property of the test signal is then detected at a monitoring point of the optical communications system, and used to estimate the associated phase nonlinearity.

Abstract: In a communication line switching method for an optical communications system in which a station-side line terminal apparatus and user-side line terminal apparatuses are connected via a plurality of redundant physical lines, the discovery of the station-side optical line terminal registering the user-side line terminal apparatuses, wherein the registered user-side line terminal apparatuses monitoring a time stamp drift error that is generated when a difference between a time stamp included in a received signal and a local time measured by the own apparatus is larger than a value set in advance and, when the time stamp drift error occurs, shifting to a deregistered state and waiting for registration by the discovery. The station-side line terminal apparatus switches a physical line from a working physical line to a backup physical line of the physical lines.

Abstract: A transmitter for a communications link is tested by using a (software) simulation of a reference channel and/or a reference receiver to test the transmitter. In one embodiment for optical fiber communications links, a data test pattern is applied to the transmitter under test and the resulting optical output is captured, for example by a sampling oscilloscope. The captured waveform is subsequently processed by the software simulation, in order to simulate propagation of the optical signal through the reference channel and/or reference receiver. A performance metric for the transmitter is calculated based on the processed waveform.

Abstract: A method of determining a round trip delay time in a network comprising receiving a gate message allocating a transmission time window; retrieving a first timestamp from the gate message; setting a first clock to the time corresponding to the first timestamp, and wherein the first clock runs synchronously with a second clock recovered from a received data stream; sending upstream, after a time interval comprising a grant start time included in the transmission time window offset by a random delay time, a registration request message, wherein the registration request message includes a second timestamp obtained from the first clock; and determining a round trip delay (RTT) from a time the registration request message is received and the second timestamp.

Abstract: An optical receiver comprising an optical-to-electrical converter and a digital processor having one or more equalizer stages. The optical-to-electrical converter is configured to mix an optical input signal and an optical local-oscillator signal to generate a plurality of electrical digital measures of the optical input signal. The digital processor is configured to process the electrical digital measures to recover the data carried by the optical input signal. At least one of the equalizer stages is configured to perform signal-equalization processing in which the electrical digital measures and/or digital signals derived from the electrical digital measures are being treated as linear combinations of arbitrarily coupled signals, rather than one or more pairs of 90-degree phase-locked I and Q signals.

Abstract: An information communication method that enables communication between various devices includes: determining a plurality of patterns of a change in luminance, by modulating a respective plurality of signals to be transmitted; and transmitting, by each of a plurality of light emitters changing in luminance according to any one of the determined plurality of patterns of the change in luminance, a signal corresponding to the pattern, wherein in the transmitting, each of the plurality of light emitters changes in luminance at a different frequency so that light of one of two types of light different in luminance is output per a time unit predetermined for the light emitter and that the time unit predetermined for the light emitter is different from a time unit predetermined for an other one of the plurality of light emitters.

Abstract: Methods and systems for encoding multi-level pulse amplitude modulated signals using integrated optoelectronics are disclosed and may include generating generating a multi-level, amplitude-modulated optical signal utilizing an optical modulator driven by two or more of a plurality of electrical input signals. The optical modulator may configure levels in the multi-level amplitude modulated optical signal. Drivers may be coupled to the optical modulator, and the plurality of electrical input signals may be synchronized before being communicated to said drivers. Two or more of said plurality of electrical input signals may be selected utilizing one or more multiplexers. The one or more multiplexers may select an electrical input or a complement of the electrical input. Phase addition may be synchronized in a plurality of optical modulator elements in the optical modulator utilizing one or more electrical delay lines. The optical modulator may be integrated on a single substrate.

Abstract: The present invention relates to light-based communication, and more particularly it relates to methods for configuration of at least one remote light-sensing device, to a central light-emitting unit and to a light-sensing device. According to the invention, spatial configuration of remote light-sensing devices (e.g. peripherals such as loudspeakers or light devices), will be achieved by transmission of embedded identifiers or configuration information in light emitted in a plurality of directions from a central light-emitting unit. With a different identifier or different configuration information for each direction of transmission, the directions can be distinguished from each other. The invention enables a user to place remote light-sensing devices in a desired spatial position and the central light-emitting unit will be able to determine location and spatial function, i.e. for example whether the peripheral is an audio device and/or a lighting device.

Abstract: An optical transmitter includes a plurality of VCSELs (vertical cavity surface emitting laser) that convert an electrical signal into an optical signal and transmit the converted optical signal. The optical transmitter measures a time for each of the VCSELs of transmitting an optical signal. Then, the optical transmitter assigns an electrical signal, indicating information to be transmitted, to one or more VCSELs, out of the VCSELs, other than a VCSEL of which a cumulative time measured is more than a predetermined threshold.

Abstract: A communication device may be operable to determine, in an optical module, a signal quality associated with each of one or more host transmitter filters in a host circuit. The signal quality may be communicated from the optical module to the host circuit via a management interface. The communication device may control, in the host circuit, configuration of each of the host transmitter filters based on the signal quality. The communication device may be operable to determine, in the host circuit, a signal quality associated with each of one or more module transmitter filters in the optical module. The signal quality associated with each of the module transmitter filters may be communicated from the host circuit to the optical module via the management interface. The communication device may control, in the optical module, configuration of each of the module transmitter filters based on the signal quality.

Abstract: According to an embodiment, a semiconductor device includes an analog/digital conversion unit, a pulse width modulation unit outputting a transmission signal, the transmission signal being a pulse pattern corresponding to a digital signal output from the analog/digital conversion unit, a reference signal generation unit generating a reference signal, the reference signal being a fixed pulse pattern. The device includes a first control unit selecting one of the transmission signal and the reference signal, a light emitting element drive unit outputting a drive current based on the transmission signal or the reference signal, a light emitting element driven by the light emitting element drive unit. The device includes an optical receiving unit converting the optical signal into a voltage signal, and a demodulation unit demodulating the voltage signal into a digital signal based on the transmission signal or the reference signal.

Abstract: Even in a network system including a transmission line of which dominant cause of delay is a transmission line delay, controlling communication speed of the network system as a whole efficiently and suppressing the delay is made possible.

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: In one embodiment, a smart small form-factor pluggable (SSFP) transceiver—compatible with SFP size, power, and interconnection standards—includes an optical transceiver, an electrical connector, a protocol processing engine, and a CPU. The SSFP transceiver is configured for use at a client site having no network interface device (NID). The SSFP transceiver (1) mates to a client's network device at an electrical interface within the network device and (2) connects to a network provider's central office (CO) node via an optical cable at an optical interface. The SSFP transceiver is configured to (1) be powered by the network device, (2) power-up upon mating with the network device, (3) be configured by a remote management agent (RMA) of the network provider for communication with the provider network, (4) respond to/generate Operation, Administration, and Management (OAM) messages from/for the CO node, and (5) provide OAM demarcation functions of a conventional NID.

Abstract: Provided is an apparatus and method for measuring IQ imbalance, and in particular, is an apparatus and method for measuring IQ imbalance for an optical receiver. The apparatus for measuring IQ imbalance for an optical receiver includes a light generating unit generating optical and reference signals to provide the optical and reference signals to an optical receiver, a graph creating unit creating a Lissajous figure by using an in-phase (I) signal and a quadrature-phase (Q) signal output from the optical receiver in response to the optical and reference signals, and a calculating unit calculating IQ imbalance for the optical receiver with reference to the Lissajous figure.

Abstract: A joint switching method for an aggregation node, an aggregation node, and an optical network protection system including an aggregation node are provided. By monitoring information transferred between an active optical line terminal (OLT) and a broadband network gateway (BNG), the aggregation node finds a fault in time according to the monitored information and when a fault occurs, the aggregation node starts a local protection solution, enables a corresponding backup port connected to a backup OLT corresponding to the active OLT, and disables an active port connected to the active OLT. Through the method, when the active OLT is switched to the backup OLT, the aggregation node performs joint switching, which ensures normal communication.

Abstract: An apparatus comprising an optical transmitter, a coarse tuner coupled to the optical transmitter and having a first tuning range, a fine tuner coupled to the optical transmitter and having a second tuning range smaller than and within the first tuning range, a wavelength division demultiplexer coupled to the optical transmitter and to a plurality of optical fibers, and a detector coupled to the optical transmitter and the wavelength division demultiplexer.

Abstract: A method and system for determining stress associated with a communication device, e.g., an optical fiber, and associated structures are disclosed. An exemplary method includes transmitting an initiated signal through a communication device, and comparing a reflected signal reflected by the communication device with the initiated signal. The method may further include determining a stress associated with the device from at least the comparison of the initiated signal and the reflected signal.

Abstract: A method and circuit are provided for implementing reduced signal degradation for fiber optic modules, and a design structure on which the subject circuit resides. Responsive to a detected signal input, an optical misalignment calculation is performed. A voltage potential for a lens shape control is selected responsive to the optical misalignment calculation. An optical signal loss calculation and threshold compare are performed. Responsive to the optical signal loss calculation less than the threshold, the lens shape and voltage potential are fixed. A fluidic lens provides variable lens shape responsive to the selected voltage potential being applied to the fluidic lens.

Abstract: Optical fiber-based wireless systems and related components and methods support radio frequency (RF) communications with clients over optical fiber, including Radio-over-Fiber (RoF) communications. The systems may be provided as part of an indoor distributed antenna system (IDAS) to provide wireless communication services to clients inside a building or other facility. The communications can be distributed between a head end unit (HEU) that receives carrier signals from one or more service or carrier providers and converts the signals to RoF signals for distribution over optical fibers to end points, which may be remote antenna units (RAUs). A microprocessor-based control system or systems may also be employed. The control systems may include one or more microprocessors or microcontrollers in one or more of the components of the system that execute software instructions to control the various components and provide various features for the optical fiber-based distributed antenna systems.

Abstract: An optical measurement instrument comprises operational modules (101-107) that are interconnected via a digital communication network (110). Each operational module comprises a transceiver (111-117) connected to the digital communication network and arranged to support a pre-determined digital communication protocol employed in the digital communication network. Those operational modules that include a detector further comprise an analog-to-digital converter (118) for converting a detected signal into a digital form and a digital circuitry (119) for providing digital information based on the detected signal with address data related to a particular operational module to which the digital information is to be delivered via the digital communication network.

Abstract: A system and method for reducing power consumption in a Passive Optic Network (PON). The system comprises an optical line terminal (OLT), an optical network unit (ONU), a traffic-detection module configured to detect status of traffic to and from the ONU, and a power-management module configured to place the ONU in sleep mode based on the detected traffic status. The ONU includes transmitting and receiving components that are selectively powered down during the sleep mode based on a type of traffic in the ONU.

Abstract: A delay interferometer includes a half beam splitter and two pentagonal prisms disposed on a substrate. The half beam splitter branches light to be measured which travels substantially in parallel with the substrate into two branched light beams. The pentagonal prisms respectively reflect the respective branched light beams such that the optical axes of the branched light beams are moved in parallel in a direction substantially perpendicular to the substrate by reflection. The half beam splitter combines the branched light beams reflected by the pentagonal prisms to generate interference light beams.

Abstract: A high-speed optical receiver implemented using a low-speed light receiving element is provided, which is configured to receive an optical signal having a higher transmission rate than that received using a general avalanche photo diode (APD) by expanding a frequency bandwidth using a receiver circuit configured together with an APD in the optical receiver including the APD, an APD bias control circuit, a transimpedance amplifier (TIA) for amplifying a signal received from the APD to have low noise, and a post amplifier; and a method of implementing such a high-speed optical receiver.

Abstract: In order to provide a transmission device which can resolve the deterioration in transmission characteristics due to lack of the resolution of a D/A converter in a high speed and large capacity digital communication, a transmission device according to an exemplary aspect of the present invention includes an encoding unit encoding input data; an unequal-interval quantization unit quantizing an output signal from the encoding unit by a quantization level number based on a resolution of a subsequent digital-to-analog conversion unit by using an unequally spaced quantization level interval based on the output signal; the digital-to-analog conversion unit converting an output signal from the unequal-interval quantization unit into an analog signal; an output level adjustment unit adjusting an output level of the digital-to-analog conversion unit so as to compensate a difference between a predetermined initial transfer function and a transfer function of the unequal-interval quantization unit; and a modulation unit

Abstract: A method comprising receiving digital samples from an optical communication system, assigning the samples into bins based on signal levels of the samples, computing an average signal level for each bin, determining a level adjustment transformation function for the samples based on the average signal levels of the bins, and applying the level adjustment transformation function to the samples. Also, disclosed is an optical receiver comprising a frontend configured to receive an optical signal over an optical channel, and convert the optical signal into a plurality of sequences of digital samples, and a processor coupled to the frontend and configured to perform a channel equalization on the samples of the sequences, assign the channel equalized samples of each sequence into bins based on signal levels of the channel equalized samples, determine a level adjustment transformation function for each sequence, and apply the level adjustment transformation function to each sequence.

Abstract: In a communication line switching method for an optical communications system in which a station-side line terminal apparatus and user-side line terminal apparatuses are connected via a plurality of redundant physical lines, the discovery of the station-side optical line terminal registering the user-side line terminal apparatuses, wherein the registered user-side line terminal apparatuses monitoring a time stamp drift error that is generated when a difference between a time stamp included in a received signal and a local time measured by the own apparatus is larger than a value set in advance and, when the time stamp drift error occurs, shifting to a deregistered state and waiting for registration by the discovery. The station-side line terminal apparatus switches a physical line from a working physical line to a backup physical line of the physical lines.

Abstract: Problems of excessive fading in systems for monitoring single-mode optical fiber for physical disturbances are addressed by launching into the fiber polarized light having at least two different predetermined launch states of polarization whose respective Stokes vectors are linearly-independent of each other; downstream from the first location, receiving the light from the fiber; analyzing the received light using polarization state analyzer means having at least two different analyzer states of polarization that are characterized by respective Stokes vectors that are linearly-independent of each other and detecting the analyzed light to provide corresponding detection signals; deriving from the detection signals measures of changes in polarization transformation properties of the fiber between different times that are substantially independent of said launch states and said detection states; and, on the basis of predefined acceptable physical disturbance criteria determining whether or not the measures are i

Abstract: One embodiment provides a system that tests optical performance in an Ethernet passive optical network (EPON), which includes an optical line terminal (OLT) and at least one optical network unit (ONU). The system configures an ONU with a circular queue that contains test frames for testing optical performance. The OLT then notifies the ONU to transmit test frames at a specified data rate for a specified duration. After receiving test frames at the OLT, the system measures frame loss and/or bit error rate based on the received test frames.

Abstract: Radio-frequency identification—(RFID)-based systems and methods for collecting telecommunications information is disclosed. The methods include storing transceiver information in a transceiver and connector information in an optical fiber connector, and then operably connecting the connector to the transceiver. The connection results in an electrical connection that allows the transceiver information to be communicated to the connector. The connector has a RFID tag that generates a connector RFID-tag signal that includes the connector information and the transceiver information. When electronics equipment are connected to the transceiver, electronics-equipment information is passed through the transceiver to the connector so that the electronics-equipment information can be included in the connector RFID-tag signal.

Abstract: An adaptive coding scheme for nonlinear channels improves reliability and an efficiency in digital communication networks. The method monitors channel statistics to analyze an extrinsic information transfer chart of the channels. The channel statistics are fed back to the transmitter to adapt forward error correction coding. A parametric analysis method uses a Gaussian mixture model. The statistical information feedback can adapt an ARQ sheme by adding a weighted received signal to the original coded signals to reduce nonlinear distortion. Trellis shaping, can make the transmitting signal preferable for nonlinear channels.

Abstract: The present invention discloses a Wavelength Division Multiplexing Filter which can satisfy coexistence requirements of different PON systems and an optical line detecting system.

Abstract: A three-way handshake method for optical messaging in a multi-domain optical network that includes a first pass from a source domain to a destination domain through intermediate domains on candidate working paths, collecting information identifying available routing resources for each working path, calculating a working path metric and storing each of the metrics at the respective border node, determining a path key of the topology of each domain working path and using the path key to identify the path outside its domain and determining the best working paths and border nodes to use. A second pass using the path keys for identifying the working path in each domain and reserving the identified routing resources and selecting which routing resources to use. A third pass identifying the selected routing resources and establishing an optical signaling message path between the source node and the destination node.

Abstract: Terminals of upstream and downstream sides of an in-service line and a detour line are connected by optical couplers. An optical oscilloscope is connected to one optical coupler, and a chirped pulse light source is connected to the other optical coupler to thereby form dualized lines. The detour line includes an optical line length adjuster for compensating for the phase difference of optical transmission signals that occurs because of the optical line length difference with the in-service line. Pulse light in which an optical frequency is chirped is transmitted from the chirped pulse light source. The pulse light is branched by the second optical coupler, passes through the in-service line and the detour line, is multiplexed again by the first optical coupler, and is measured by the optical oscilloscope.