Abstract: A detecting device that detects insertion loss of fiber route and return loss of individual events in an optical fiber network based on signals from dual paths to obtain various kinds of reference information of the optical fiber network. When the first path is selected, a detection signal produced using frequency modulated continuous wave (FMCW) technique is output to the optical fiber network. A return signal of the detection signal is used to analyze the position and return loss of various events in the optical fiber network. When the second path is selected, a common detection light is output to the optical fiber network. Based on the return signal of the common detection light, the insertion loss and total return loss of the entire network are obtained.

Abstract: The present invention relates to the field of communication transmission, and in particular, to a method for generating a probe pulse and a coherent optical time domain reflectometer. The coherent optical time domain reflectometer includes: a control unit, configured to generate a first pulse signal and a second pulse signal which have a same period T, where the second pulse signal lags behind the first pulse signal, and T satisfies T?t+2L/C; a driving unit, configured to generate a frequency change driving signal according to the first pulse signal; a continuous light laser device, configured to generate, as driven by the frequency change driving signal, continuous light having a changing frequency and an unchanging frequency spectrum width; and a probe pulse generating unit, configured to modulate the continuous light according to the second pulse signal to generate a probe pulse.

Abstract: A transmission-path-type specifying apparatus includes an optical filter that extracts a plurality of different wavelength components from light including wavelength components occurring at the time of communication; an optical switch that simultaneously transmits same pulse signals superposed on light of the extracted wavelength components. The apparatus also includes an ASE modulation controlling unit that obtains a delay-time difference among the transmitted pulse signals when arriving at a destination via a transmission path; a characteristic-value calculating unit that calculates a characteristic value of the transmission path corresponding to a reference time varied depending on the obtained delay-time difference and a type of the transmission path; and a fiber-type determining unit that specifies the type of the transmission path based on the calculated characteristic value.

Abstract: The disclosure claims a method and system for detecting optical fiber connection.

Abstract: A method includes generating a test signal and modulating the test signal. The method may also include transmitting the test signal on an optical path, where the optical path may include a number of add-drop multiplexer devices and amplifiers. The method may also include receiving the test signal at a destination device and converting the received test signal into an electrical signal. The method may further include identifying a portion of the electrical signal that is associated with the modulated test signal.

Abstract: A dispersion compensation design system includes a changing unit setting a changed value for the amount of dispersion compensation for a span connecting nodes constituting an optical network; a path classification unit determining whether respective paths in the optical network are capable of transmission with the changed value and classifying one or more of the paths as second category paths based on the determination results; an updating unit updating the amount of dispersion compensation with the changed value if the number of the second category paths in the latest classification result is less than the number of the second category paths in the retained previous classification result; and a repeating unit that, if not all of the paths in the optical network are capable of transmission, prevents use of combinations of amounts of dispersion compensation applied to the spans in the second category paths in the latest classification result.

Abstract: Various embodiments provide for detection of tapping of an optical signal. In one embodiment an optical fiber includes a cladding region and first and second core regions. The first core region has a first core medium having a first mode-dependent loss (MDL) figure of merit. The second core region has a second core medium having a second different MDL figure of merit. Tapping of the optical signal may be determined to occur when the MDL of the first and second optical signals differs by a predetermined threshold value.

Abstract: A remotely controlled fiber testing method has the steps of: building a fiber network system including a local fiber station and a remote fiber station; sending a modulated signal to the remote fiber station by the local fiber station; demodulating the modulated signal to obtain a control command by the remote fiber station; executing the control command to obtain a testing result by the remote fiber station; modulating the testing result and sending the testing result back to the local fiber station; and demodulating the testing result by the local fiber station. Only one technician appointed to the local fiber station is sufficient to do the testing action. Therefore, the personnel cost is effectively reduced.

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: A method of automated testing and evaluation of a node of a communications network, the method comprising: a management computer interacting with the node to discover fibre trails within the node that can be safely tested; and the management computer interacting with the node to test at least continuity of each identified fibre trail that can be safely tested

Abstract: Optical amplification stage (1) for OTDR monitoring, comprising a first (2a) and a second optical signal path (2b), a first (3a) and a second optical amplifier (3b), a first optical coupler (4a) placed along the first optical signal path downstream the first optical amplifier, a second optical coupler (4b) placed along the second optical signal path downstream the second optical amplifier, an optical by-pass path (5) optically connecting the first and the second optical coupler, a first (11a) and a second optical reflector (11b) optically connected to respectively the first and second optical coupler, and an optical filter (10) placed along the optical by-pass path which has attenuation high on the whole WDM band and low at the OTDR wavelength(s).

Abstract: The invention relates to a system and method of dispersion measurement in an optical fiber network. The invention provides means for transmitting from a transmitting node, using a single tunable laser transmitter, two consecutive bursts of data at different wavelengths ?1 and ?2 to a receiver node, wherein each burst of data comprises a unique sequence of amplitude modulated data, and wherein the two sequences are injected with a fixed known delay. The delay between the two consecutive bursts of data is maintained by selective switching of the tunable laser, such that clock recovery circuitry at the receiver node remains locked during the delay between the two bursts. The dispersion measurements method of the present invention is based on walk off and bit position detection between two wavelengths suitable for fast optical burst switching network is described. This method does not require an operator, extra equipment, or traffic interruption on the network.

Abstract: A data processing device is connectable to a communication network and operable to receive data associated with an attenuation characteristic of a transmission line of a cable in a cable communication subsystem, the subsystem comprising a transmitter and/or receiver coupled to the cable. The data processing device is responsive to the received data to initiate a security procedure.

Abstract: A computer device may include logic configured to receive a selection of a start node and an end node in an optical network and obtain network topology information relating to the optical network. The logic may be further configured to determine link latencies for particular links in the optical network; determine a least latency path between the start node and the end node based on the obtained network topology information and the determined link latencies, and wherein the least latency path includes one or more of the particular links; determine one or more alternate paths to the determined least latency path; determine channel availability for the least latency path and the one or more alternate paths; and generate a user interface that relates the least latency path and the one or more alternate paths to the determined channel availability.

Abstract: In one example embodiment, an optoelectronic communications assembly having an optical receiver or an optical transmitter includes an optical interface disposed at an end thereof and through which optical signals are communicated by the optical receiver or optical transmitter. The optoelectronic communications assembly also includes an electronic component and a first electrical interface disposed at the optical interface end of the optical communications assembly and communicatively coupled to the electronic component.

Abstract: A detecting method, an apparatus, and a system in an Optical Distribution Network (ODN) are provided. The method includes: an Optical Line Termination (OLT) reserves a test window, and an Optical Network Unit (ONU) stops sending an uplink signal in the test window, the OLT emits a downlink test signal having a wavelength the same as that of the uplink signal in the test window, the OLT receives backward signals of the downlink test signal, in which the backward signals include a backward scattered signal and a backward reflected signal, processes the backward signals, and obtains state information of the ODN according to the backward signals. The method does not need to add other hardware, and the downlink signal is sent normally in the downlink. The implementation is low in the cost and easy in the technology.

Abstract: In general, techniques are described to detect potential issues with optical fibers. The techniques may be implemented using various optical network hardware. An example optical network unit (ONU) includes a network interface coupled to an optical fiber through which the ONU communicates with an optical line terminal (OLT). The ONU further includes a control unit that determines at least a first signal strength and a second signal strength of a signal received via the optical fiber, determines a rate of signal strength degradation based on the first signal strength and the second signal strength, compares the rate of signal strength degradation to a rate threshold so as to determine a potential issue with the optical fiber, and based on the comparison, causes the network interface to send a message to the OLT indicating a potential issue with the optical fiber to which the ONU connects to communicate with the OLT.

Abstract: A method and a device for an optical power budget in a passive optical network are disclosed in the present invention, wherein said method includes: acquiring a corresponding minimum optical link loss according to a transmission requirement of a passive optical network with a large splitting ratio or long distance (710); selecting an optical transmitter with large power and an optical receiver with high sensitivity as a combination of an optical transmitter of an Optical Line Terminal (OLT) and an optical receiver of an Optical Network Unit (ONU) in an optical link, as well as a combination of an optical receiver of the OLT and an optical transmitter of the ONU in the optical link according to the minimum optical link loss to compose a passive optical network system comprising the OLT, an Optical Distribution Network (ODN), and ONUs connected in sequence (720).

Abstract: A method includes sweeping an optical frequency of an optical signal by an optical transmitter controlling an electric-field information signal corresponding to a transmitted signal, providing different polarization states for individual frequencies of the optical signal by the optical transmitter controlling a mixture of a first electric-field information signal corresponding to a first transmitted signal and a second electric-field information signal corresponding to a second transmitted signal, obtaining, for individual frequencies of the optical signal, polarization dependent characteristics corresponding to different frequencies, when the optical transmitter sweeps the frequency of the optical signal, by an optical receiver calculating a polarization-dependent characteristic of an optical transmission line between the optical transmitter and the optical receiver, based on items of received-electric-field information corresponding to the different polarization states, and obtaining statistical information

Abstract: A method and system to economically monitor an optical OOK signal that can detect perceptible changes in signal quality and identify the type of optical impairment causing the change. The invention requires a new and novel combination of known techniques to create an eye diagram of the transmitted pulse in a wavelength division multiplexing systems and then removing the noise from the eye diagram. Economy of operation is achieve by using asynchronous sampling techniques for generating the eye diagram. The resulting “cleaner” eye diagram is then analyzed to identify any changes in performance. In the preferred embodiment, the analysis is conducted on histograms generated from eye diagram, the histograms are computed at a number of points across the optical signal pulse period.

Abstract: A detecting device that detects insertion loss of fiber route and return loss of individual events in an optical fiber network based on signals from dual paths to obtain various kinds of reference information of the optical fiber network. When the first path is selected, a detection signal produced using frequency modulated continuous wave (FMCW) technique is output to the optical fiber network. A return signal of the detection signal is used to analyze the position and return loss of various events in the optical fiber network. When the second path is selected, a common detection light is output to the optical fiber network. Based on the return signal of the common detection light, the insertion loss and total return loss of the entire network are obtained.

Abstract: A method includes outputting an optical signal from an optical transmitter; causing the optical signal to propagate through equipment of an optical communication site and to loop back to an optical receiver; measuring optical powers, respectively, based on taps proximate to the optical transmitter and the optical receiver; calculating an optical power loss based on the optical powers measured; determining whether the optical power loss is an acceptable value; and indicating when the optical power loss is not the acceptable value.

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: An optical transmission apparatus in an optical transmission system that transmits an optical signal through a transmission fiber includes a measurement device that measures Raman gain efficiency of the transmission fiber; a level determiner that determines an input level of the optical signal based on Raman gain efficiency measured by the measurement device; and a controller that controls a level of the optical signal input to the transmission fiber to become the input level determined by the level determiner.

Abstract: A method for monitoring wavelength-division multiplexed (WDM) signal for detecting signal drift of objective signals, including generation of one or more objective signals and a guard signal. The guard signal has a wavelength that is within a range defined by a guard channel. The first and second objective signals and the guard signal are wavelength-division multiplexed to generate a wavelength-division multiplexed signal. The first objective signal, the second objective signal, and the guard signal are assigned to a first multiplexed objective channel, a second multiplexed objective channel, and a multiplexed guard channel, respectively. The wavelength-division multiplexed signal is received by a monitor and then the error rate of the multiplexed guard channel is determined.

Abstract: An optical communication system has a power dissipating element that is thermally coupled to an optical transmitter. The currents supplied to the transmitter and the power dissipating element are controlled such that the sum of such currents is constant. Accordingly, temperature fluctuations in the transmitter due to patterns in the transmitted data are prevented or at least reduced, thereby reducing thermal tails on measurements. In one exemplary embodiment, a light source is used as the power dissipating element, and the output of such light source is beneficially used to probe another optical fiber or to enhance the OTDR performance or analysis.

Abstract: An optical channel monitor includes: a first optical device to include first, second and third optical ports, light input through the first optical port being led to the second optical port, light input through the second optical port being led at least to the third optical port; a second optical device to include fourth, fifth and sixth optical ports, light input through the fourth optical port being led to the fifth optical port, light input through the fifth optical port being led at least to the sixth optical port; an optical filter to include seventh and eighth optical ports optically connected to the second and fifth optical ports, respectively, a specified wavelength being transmitted between the seventh and eighth optical ports; a first photo detector to detect light output from the sixth optical port; and a second photo detector to detect light output from the third optical port.

Abstract: An OLT operable in a PON and structured to perform OTDR measurements. The OLT comprises an electrical module for generating continuous downstream signals and processing received upstream burst signals according to a communication protocol of the PON; an optical module for transmitting continuous optical signals over a first wavelength, receiving optical upstream burst signals over a second wavelength, and transmitting optical upstream burst signals over a third wavelength, wherein the optical module further includes an ONU traffic processing module being electrically coupled to the optical module and the electrical module, wherein the ONU traffic processing module is configured to emulate one of a plurality of ONUs of the PON, to generate an analysis pattern to be transmitted as an optical upstream burst signal over a third wavelength, and analyze an analysis pattern received in an optical upstream burst signal for the purpose of performing the OTDR measurements.

Abstract: A method, for determining a maximum transmission distance (Dmax) for an optical link comprising heterogeneous types of optical fibre segments, comprising: for a type of optical fibre present in said optical link: retrieve a maximum transmission reach (Mi), determine along said optical link, a length (xi) of optical fibre of said type, to reach a distance (D), normalize said length (xi), by multiplying said length (xi) by a weight (?i) function of said maximum transmission reach (Mi), sum said normalized lengths for a plurality of types of optical fibre, determine the maximum transmission distance (Dmax) of the optical link as the distance (D) for which said sum equals a given threshold.

Abstract: The present invention provides a nonlinear estimating apparatus and method, and a receiver. The nonlinear estimating apparatus includes: an information sequence acquiring unit, configured to acquire a symbol information sequence of the pulse signal inputted by a transmitting side; a perturbation quantity generating unit, configured to calculate the weighted sum of the interaction items of the pulses on one or more moments relative to the current moment, so as to obtain an additive perturbation quantity and a multiplicative perturbation quantity produced on a transmission link with a certain length; and a signal estimating unit, configured to estimating the signal received at a receiving side according to the symbol information sequence, the additive perturbation quantity and the multiplicative perturbation quantity. With the embodiments of the present invention, the accuracy of estimation of nonlinear signals may be further improved.

Abstract: An optical fiber has two or more core regions disposed within a common cladding region. Each of the core regions is configured to guide a respective light transmission comprising at least one optical mode along the length of the fiber. The cores are arranged within the common cladding region according to a core configuration that substantially prevents crosstalk between modes of neighboring cores in the fiber, in a deployment of the fiber in which cross-coupling between neighboring cores is affected by perturbations arising in the deployed fiber.

Abstract: Photonic link information collection and advertisement systems and methods enable photonic nodes (e.g., optical amplifiers) to operate within a control plane system in a distributed and real-time manner. For example, the photonic nodes may not require full control plane protocol stacks at each photonic node. In particular, the systems and methods provide a distributed discovery method for photonic links without requiring full participation in the control plane at the photonic nodes. Additionally, the systems and methods include network databases with amplifier configuration information in a control plane enabled network.

Abstract: A modulation method of an optical modem and a signal transmission apparatus performing the method are disclosed. The modulation method of the optical modem includes an optical interface providing a signal to a light source, a photo detector receiving reflected light by an optical link when output light from the light source based on the provided signal is reflected by the optical link, the photo detector measuring and determining characteristics of the optical link using the reflected light, and the optical modem determining a power level and a modulation method for each subcarrier based on the characteristics of the optical link.

Abstract: Having a fast method to perform impairment evaluation is useful for many networks. A method or corresponding apparatus according to an example embodiment of the present invention maintains a traffic engineering database of values representing characteristics of links in the network through storage of integer values representing advertised optical signal capabilities of links between the multiple optical nodes. The example embodiment determines a path through the network for optical wavelengths to be supported by the links represented in the database as a function of evaluating optical signal characteristics at each link along a possible path using the advertised optical signal capabilities and provides a selected path meeting an acceptable integrity of the optical wavelengths to a path establishment module to establish the path through the optical network. Example embodiments significantly reduce computational complexity associated with impairment evaluation and path selection in an optical network.

Abstract: The invention provides a fiber optic training kit for demonstrating and/or measuring fiber optic, fiber optic communication and fiber optic network characteristics comprises plurality of laser sources, plurality of PIN diode photo detectors. The fiber optic training kit includes a fiber Bragg grating block, a four channel multiplexing and de-multiplexing block, a fiber optic 50/50 coupler or splitter block, 980/15xx nm WDM coupler block, an erbium doped fiber optic amplifier block, a microcontroller, a function generator, a digital storage oscilloscope block, a variable optical attenuator block and a multi-meter arranged suitably in a pack with appropriate connections to power supply and a computer for the purpose of programming the microcontrollers, data recording and/or displaying the results.

Abstract: Systems and methods of compensating for transmission impairment are disclosed. One such method includes receiving a polarization-division multiplexed optical signal which has been distorted in the physical domain by an optical transmission channel, and propagating the distorted polarization-division multiplexed optical signal backward in the electronic domain in a corresponding virtual optical transmission channel.

Abstract: The present disclosure provides dynamic performance monitoring systems and methods for optical networks to ascertain optical network health in a flexible and accurate manner. The present invention introduces accurate estimations for optical channel performance characteristics based either on existing channels or with a dynamic optical probe configured to measure characteristics on unequipped wavelengths. Advantageously, the dynamic performance monitoring systems and methods introduce the ability to determine physical layer viability in addition to logical layer viability.

Abstract: To provide a polarization-diverse, heterodyne optical receiving system, a light signal is transmitted into an optical fiber having a plurality of optical sensors that are distinguishable using a multiplexing arrangement. A return light signal from the optical fiber is mixed with an optical local oscillator light signal, where the mixing outputs plural output signal portions having different polarizations. A birefringence of a particular optical sensor is determined based on the plural signal portions.

Abstract: Described herein are systems and methods for enhancing the resolution of an optical time-domain reflectometer (“OTDR”). One embodiment of the disclosure of this application is related to a device, comprising an optical measuring component collecting a first set of measurement data from a forward trace along an optical fiber with the optical measuring device using depolarized light, and a processing component calculating loss along the length of fiber. The optical measuring device further collects a second set of measurement data from a backward trace along the optical fiber with the optical measuring device using depolarized light.

Abstract: A network comprises nodes connected by optical sections. The nodes support a plurality of traffic types. A candidate optical path having a first traffic type is selected as a routing for at least part of the connection on the basis of at least one routing metric. Pre-computed parameters are retrieved for the optical sections of the candidate optical path. The pre-computed parameters are indicative of quality of transmission along the optical section for the first traffic type. A quality of transmission is determined along the candidate optical path using the retrieved parameters. The pre-computed parameters for each of the optical sections can be used at a network planning tool and then exported to a network management system or a path computation entity at a node for creating a validation module for use in validating connections across the optical transmission network.

Abstract: A spatially multiplexed optical link having a plurality of transmission paths, wherein at least one transmission path is configured to carry an optical-pump signal while one or more other transmission paths carry data-bearing signals. Disposed within the optical link are an optical signal-distribution module and an amplifier module. The optical signal-distribution module is configured to couple portions of the optical-pump signal into the data-bearing transmission paths. The amplifier module is configured to amplify the data-bearing signals using these portions of the optical-pump signal as a power source in a suitable all-optical amplification scheme. The optical-pump signal can optionally be tapped and applied to a photovoltaic element configured to directly power a device, e.g., an optical performance monitor, or to charge the battery of that device to enable its autonomous operation if external electrical power is not available where the device is deployed.

Abstract: Various example embodiments are disclosed. According to one example embodiment, a phase error is estimated in a series of digital symbols of a phase-modulated signal, where the signal is subject to a non-linear phase shift error due to transmission of the signal through an optical fiber. A phase correction of an instant digital symbol that succeeds the series of digital symbols is estimated, where the estimated phase correction is based on the estimated phase errors in the series of digital symbols. The estimated phase correction of the instant digital symbol is limited to a maximum absolute value, and the estimated phase correction is applied to the instant digital symbol of the signal.

Abstract: Various embodiments of the present invention are directed to sensor networks and to methods for fabricating sensor networks. In one aspect, a sensor network includes a processing node (110, 310), and one or more sensor lines (102,202,302) optically coupled to the processing node. Each sensor line comprises a waveguide (116,216,316), and one or more sensor nodes (112,210). Each sensor node is optically coupled to the waveguide and configured to measure one or more physical conditions and, encode measurement results in one or more wavelengths of light carried by the waveguide to the processing node.

Abstract: A method for detecting branch fibers is provided, which includes: sending test signals to a plurality of branch fibers, where the test signals are added at ports of the optical splitting module with identification information for identifying branch fibers connected to the ports; and receiving a reflection signal added with the identification information of a detected branch fiber, identifying the detected branch fiber corresponding to the reflection signal through detecting the identification information added to the reflection information, and obtaining channel characteristics of the detected branch fiber according to the reflection signal. Further, a system and an apparatus for detecting branch fibers are provided.

Abstract: A system and method is disclosed that allows for the monitoring, analyzing and reporting on performance, availability and quality of optical network paths. The correlation of PM parameter metrics to client connections, coupled with threshold-based alarm generation provides a proactive and predictive management, reporting and analyzing of the health and effectiveness of individual path connections to alert Operational Support (OS) staff and/or customers to signal degradation and impending Network Element (NE) failures. The system and method performs in real-time processing intervals required for alarm surveillance in a telecommunications network.

Abstract: An optical line monitoring apparatus, including: a group information recording portion which records group information about to which splitter respective terminators are connected; a normal information recording portion which records intensities of reflected lights from a plurality of terminators in a state in which a failure is not occurring in optical lines; a monitored information recording portion which records intensities of reflected lights from the plurality of terminators in failure monitoring time; an attenuation amount determination portion which determines a terminator the reflected light intensity of which is attenuated compared with the corresponding reflected light intensity in normal information; and a control portion which determines, if the intensities of the reflected lights of all the terminators connected to the same splitter are attenuated by the same value, that a failure has occurred between the test apparatus and the splitter to which all the terminators are connected.

Abstract: An optical communication apparatus that includes multiple optically communicative components positioned optically in series. Some of the optically communicative components may be optical fiber segments of perhaps different types. The optical channel represented by the series of optically communicative components and approximates a transfer function of an optical channel of a longer optical fiber. Accordingly, rather than deal with a lengthy optical fiber, an apparatus having a shorter optical channel may be used instead. The construction of the optical communicative components may be calculating an input transfer function. The construction would include an ordering of discrete optically communicative components that, when placed optically in series, simulates an estimation of a particular transfer function. Testing may then occur by actually passing an optical signal through the series construction of optically communicative components, rather than through the longer optical fiber.

Abstract: Embodiments include methods, apparatus, and systems for cable monitoring. One embodiment includes a method that receives data from an optical transceiver coupled to a cable and a RFID (radio frequency identification) device mounted to the cable. The data from the optical transceiver and RFID device is used to determine an operational status of the cable.

Abstract: The differential group delay is measured in an optical fiber connection for an optical signal undergoing a phase modulation BPSK or DPSK by a digital signal at a given rate. A polarization controller at an emerging end of the connection scans polarization states of the modulated optical signal. An emulator iteratively introduces an additional delay in the modulated optical signal emerging from the connection and combines the delayed modulated optical signal and the non delayed modulated optical signal which are both polarized along two orthogonal axes into a resulting optical signal. A polarization controller and a fixed polarizer select a polarization state in the resulting optical signal along one of bisecting lines of the orthogonal axes into a linearly polarized signal. An eye diagram or a spectrum of the polarized signal is acquired by a digital oscilloscope or an optical spectrum analyzer to determine the differential group delay.

Abstract: A method for determining a value of chromatic dispersion compensation in an optical network including a plurality of nodes connected by at least one transmission line, the plurality of nodes including a plurality of dispersion compensators, the optical network including a plurality of wavelength paths between the optional nodes, the method includes determining a compensation value of the dispersion compensators in the optical network by the computer, the compensation value selecting that an error between the object value of the residual chromatic dispersion in accordance with of the first end node of the first path and the permissible value of the residual chromatic dispersion of the first end node of the first path is least, and the value of the residual chromatic dispersion of the first end is in the permissible value of the residual chromatic dispersion of the second end node of the second path.