JP2019128186A - Optical transceiver - Google Patents

Abstract

To detect failure points over a longer distance while suppressing a decrease in resolution in a detection of failure points using pulsed light.SOLUTION: The optical transceiver includes a modulation unit for outputting pulsed light to a transmission path as an inspection signal, a conversion unit for generating an electrical signal by converting a reflected light caused by the pulsed light reflected or scattered in the transmission path, a wavelength dispersion compensation unit for performing wavelength dispersion compensation for the electrical signal, a return light detecting unit for detecting the electrical signal derived from a return light caused by the pulsed light reflected at the failure point of the transmission path in the electrical signal with wavelength dispersion compensation performed, and an analysis unit for determining the failure point on the basis of the electrical signal derived from the return light.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical transceiver.

  When the characteristics of the optical fiber deteriorate due to any cause during the operation of the optical communication system, an OTDR (Optical Time Domain Reflectometer) apparatus (see, for example, Patent Document 1) is used to identify the cause. By using OTDR, it is possible to examine at which point breakage or bending occurs. The OTDR may use pulsed light as an inspection signal. When the distance from the installation position of the OTDR device to the failure location is long, the power of the returning pulse light may be reduced due to the influence of chromatic dispersion. Conventionally, in order to solve such a problem, pulsed light with a narrow frequency band (pulsed light with a wide time interval) has been used.

Japanese Patent No. 5941877

  However, when pulse light having a narrow frequency band is used, there is a problem that the resolution of the failure point is lowered.

  In view of the above circumstances, an object of the present invention is to provide an optical transceiver capable of detecting a failure location over a longer distance while suppressing a decrease in resolution in detection of a failure location using pulsed light. Yes.

  One embodiment of the present invention is a modulator that outputs pulsed light as a test signal to a transmission line, and an electric signal by converting reflected light that is generated by the pulsed light being reflected or scattered in the transmission line. In the conversion unit to be generated, the chromatic dispersion compensation unit that performs chromatic dispersion compensation on the electrical signal, and the electrical signal that has been subjected to chromatic dispersion compensation, the pulsed light is reflected at the failure point of the transmission path. The optical transmitter / receiver includes: a return light detection unit that detects an electric signal derived from the generated return light; and an analysis unit that determines the failure location based on the electric signal derived from the return light.

  One aspect of the present invention is the optical transmitter / receiver described above, wherein the analysis unit performs processing of chromatic dispersion compensation in the chromatic dispersion compensation unit when acquiring time until the return light reaches the device. Get the time except for the time it took to

  One embodiment of the present invention is the optical transmitter / receiver as described above, further comprising a control unit that determines the compensation amount of the chromatic dispersion compensation in the chromatic dispersion compensation unit.

  One aspect of the present invention is the optical transceiver described above, wherein the control unit performs control so that pulse light with a narrow pulse width is output in order in the modulation unit, and is estimated based on each pulse light. The amount of compensation is determined according to the location of the failure.

  One aspect of the present invention is the optical transceiver described above, wherein the control unit controls the chromatic dispersion compensation unit so that the chromatic dispersion compensation is performed with a plurality of different compensation amounts, and each chromatic dispersion compensation is performed. The amount of compensation is determined according to the result.

  According to the present invention, in detection of a failure point using pulsed light, it is possible to detect a failure point over a longer distance while suppressing a decrease in resolution.

It is a functional block diagram showing composition of an optical transceiver. It is a functional block diagram which shows the other structure of an optical transceiver. It is a functional block diagram which shows the further another structure of an optical transceiver. It is a figure which shows the test | inspection signal of a pulse. It is a graph which shows the time change of the electric power of the electric signal which reflected light was converted. It is a figure which shows the specific example of the outline of the analysis processing which DSP performs. It is a functional block diagram showing composition of DSP. It is a figure which shows the adjustment method of the test | inspection signal in order to improve measurement quality. It is a figure which shows the example of application to WDM of an optical transceiver. It is a figure which shows the other application example to WDM of an optical transceiver. It is a figure which shows the relationship between the pulse width of pulsed light, and electric power. It is a figure which shows the relationship between the pulse width of pulsed light, and electric power.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In this embodiment, a circulator or the like is added to an optical transceiver used in digital coherent optical transmission, and a transmission characteristic measurement function equivalent to that of OTDR is provided. This enables measurement using an optical transceiver when a failure occurs in the optical communication system.

  FIG. 1 is a functional block diagram showing a configuration of an optical transceiver 1 according to an embodiment of the present invention, and only functional blocks related to the present embodiment are extracted and shown. An optical transceiver 1 shown in the figure includes a DSP (Digital Signal Processor) 10, a DAC (Digital Analog Converter) 11, an LD (Laser Diode) 12, an IQM (IQ Modulator) 13, a circulator 14, and a SW (switch). ), ICR (Integrated Coherent Receiver) 16, and ADC (Analog Digital Converter) 17. A configuration corresponding to the DAC 11 and the ADC 17 may be provided inside the DSP 10.

  The optical transceiver 1 is different from a conventional C-OTDR (coherent OTDR) in that it has a transceiver mode and an OTDR mode inside the DSP 10. The optical transceiver 1 performs signal transmission of, for example, 100 G (giga) or more than 100 G in the transceiver mode. The optical transceiver 1 outputs an inspection signal in the OTDR mode, receives return light, and measures the characteristics of the fiber.

  The DSP 10 generates an electric signal according to the mode, and outputs the electric signal to the IQM 13 via the DAC 11. The DSP 10 also receives an electrical signal from the ICR 16 through the ADC 17 and performs demodulation processing or measurement processing according to the mode. In the measurement process, measurement on the transmission line is performed. The DAC 11 performs digital-analog conversion processing on the digital electric signal output from the DSP 10. The DAC 11 outputs an analog electrical signal to the IQM 13. The LD 12 generates laser light of a predetermined wavelength. The IQM 13 modulates the electrical signal input from the DSP 10 with the light generated by the LD 12 to generate an optical modulation signal. The circulator 14 has three ports, and outputs an optical signal input from one port to the next port. The circulator 14 receives the optical signal output from the IQM 13 and outputs the optical signal to the transmission path, and receives the reflected light from the transmission path and outputs the reflected light to the SW 15. The SW 15 switches between input of an optical signal transmitted from another optical communication device and transmitted through the transmission path, and reflected light output from the circulator 14. The SW 15 outputs the input signal to the ICR 16. The ICR 16 is configured using, for example, a 90-degree optical hybrid and a light receiving element (PD: Photo Diode). The ICR 16 converts the light modulation signal input from the SW 15 into an electrical signal by the light generated by the LD 12. The ADC 17 performs analog-digital conversion processing on the analog electric signal generated by the ICR 16. The ADC 17 outputs a digital electrical signal to the DSP 10. The transmission line is, for example, an optical fiber.

  In the present embodiment, when a failure occurs in the optical communication system, the mode is changed based on control from the control device 20 provided together with the optical transceiver 1, and the signal transmitted and received by the optical transceiver 1 is switched. Such a control device 20 is configured using, for example, a processor such as a field-programmable gate array (FPGA) or a central processing unit (CPU). It is assumed that OTDR is used when a problem occurs in the optical fiber that connects the receiving unit of the optical transceiver of the other station facing the transmitting unit of the optical transceiver of the local station. However, if there is no problem with the optical fiber connecting the transmitting unit of the optical transceiver of the other station and the receiving unit of the optical transceiver of the own station, the path is in communication and the receiving unit of the own station cannot be used. Therefore, in the case of using the OTDR mode, it is desirable that the optical fiber connecting the own station and another station be identical. Also, the control device 20 may be provided inside the optical transceiver 1.

  Subsequently, the operation of the optical transceiver 1 in each mode will be described. First, the operation of the transceiver mode will be described. The optical transceiver 1 sets the transceiver mode in the DSP 10 and sets the input from the transmission path in the SW 15 in accordance with the input control signal. The DSP 10 converts transmission data into an electrical signal, and outputs the electrical signal to the IQM 13 via the DAC 11. The DAC 11 converts a digital electrical signal into an analog electrical signal. The IQM 13 (modulation unit) modulates an analog electric signal into an optical signal by light generated by the LD 12 and outputs the optical signal. The circulator 14 outputs the optical signal input from the IQM 13 to the transmission path, receives the reflected light from the transmission path, and outputs the reflected light to the SW 15. The SW 15 receives an optical signal from the transmission line and outputs the optical signal to the ICR 16. The ICR 16 (converter) converts the light signal input from the SW 15 into an electrical signal by the light generated by the LD 12. The ADC 17 converts the analog electrical signal generated by the ICR 16 into a digital electrical signal. The DSP 10 demodulates the electrical signal input from the ADC 17 into received data.

  Next, the operation of the OTDR mode will be described. The optical transceiver 1 sets the OTDR mode in the DSP 10 and sets the input from the circulator 14 in the SW 15 in accordance with the input control signal. The DSP 10 generates an electrical inspection signal and outputs it to the IQM 13 via the DAC 11. The DAC 11 converts a digital electrical signal into an analog electrical signal. The IQM 13 modulates an analog inspection signal into an optical signal by the light generated by the LD 12 and outputs it. The optical signal for inspection output from the IQM 13 is pulsed light having a predetermined time width. The circulator 14 outputs the optical signal input from the IQM 13 to the transmission path, receives the reflected light from the transmission path, and outputs the reflected light to the SW 15. The SW 15 receives the reflected light output from the circulator 14 and outputs it to the ICR 16. The ICR 16 converts the reflected light input from the SW 15 into an electrical signal by the light generated by the LD 12. The ADC 17 converts the analog electrical signal generated by the ICR 16 into a digital electrical signal. The DSP 10 analyzes the measurement items in the same manner as the conventional OTDR, using the inspection signal converted into the electrical signal. The measurement item is, for example, determination of abnormal places such as loss, reflection, and bending.

Another configuration of the optical transceiver of the present embodiment will be described using FIGS. 2 and 3.
FIG. 2 is a functional block diagram showing the configuration of the optical transceiver 1a, and only functional blocks related to the present embodiment are extracted and shown. In the figure, the same parts as those of the optical transceiver 1 shown in FIG. The optical transceiver 1a differs from the optical transceiver 1 shown in FIG. 1 in that it includes an ATT (attenuator) 21, an ATT 22 and a coupler 23 instead of the SW 15.

  In the transceiver mode, the ATT 21 attenuates the light output from the circulator 14 so as to be close to 0 and outputs it to the coupler 23, and the ATT 21 inputs an optical signal from the transmission line and outputs it to the coupler 23 without attenuation. On the other hand, in the ODTR mode, the ATT 21 outputs the light output from the circulator 14 to the coupler 23 without being attenuated, and the ATT 21 attenuates the optical signal input from the transmission path to be close to 0 and outputs it to the coupler 23. The coupler 23 combines the light output from the ATT 21 and the light output from the ATT 22 and outputs the combined light to the ICR 16. Damping control as to whether or not the ATTs 21 and 22 perform damping is performed based on a control signal from the outside (for example, the control device 20).

  FIG. 3 is a functional block diagram showing the configuration of the optical transceiver 1b, and shows only functional blocks related to the present embodiment. In the figure, the same components as those of the optical transceiver 1 shown in FIG. The optical transceiver 1b differs from the optical transceiver 1 shown in FIG. 1 in that a coupler 31, an attenuator 32, an attenuator 33, and a coupler 34 are provided instead of the circulator 14 and the SW 15. The attenuators 32, 33 may be VOAs (variable optical attenuators) or ATTs that attenuate light of a predetermined wavelength. When the attenuators 32 and 33 are VOAs, the attenuator 32 attenuates the wavelength of the optical signal received in the transceiver mode, and the attenuator 33 attenuates the wavelength to be measured. The configuration of the optical transceiver 1b is compatible with the structure of the conventional optical transceiver.

  The coupler 31 branches the signal input from the IQM 13 into a transmission path, an attenuator 32, and a monitor. In the transceiver mode, the attenuator 32 attenuates the light output from the coupler 31 so as to be close to 0 and outputs it to the coupler 34, and the attenuator 33 outputs it to the coupler 34 without attenuating the optical signal input from the transmission line. To do. On the other hand, in the ODTR mode, the attenuator 32 outputs the light output from the coupler 31 to the coupler 34 without being attenuated, and the attenuator 33 attenuates the optical signal input from the transmission path so as to be close to 0, thereby reducing the coupler 34. Output to. The coupler 34 combines the light output from the attenuator 32 and the light output from the attenuator 33, and outputs the combined light to the ICR 16 and a monitor. Attenuation control of whether or not the attenuators 32, 33 perform attenuation is performed based on a control signal from the outside (for example, the control device 20). When the attenuators 32 and 33 are VOAs, the wavelength for which attenuation control is to be performed is also performed based on a control signal from the outside (for example, the control device 20).

  As described above, the mode switching between the OTDR mode and the signal reception mode (transceiver mode) of the optical transceiver 1a is performed by the ATTs 21 and 22, and the mode switching of the optical transceiver 1b is performed by the attenuators 32 and 33. The frequency of switching between the OTDR mode and the signal reception mode is bursty or continuous. In the case of burst signal transmission, the optical transceivers 1, 1a, 1b perform measurements while receiving the burst signal.

  The inspection signal in the OTDR mode includes pulsed light similar to that in normal OTDR.

  FIG. 4 is a diagram showing an inspection signal configured using pulsed light. The DSP 10 generates a pulse inspection signal. The pulse inspection signal generated by the DSP 10 is converted into an analog signal by the DAC 11. An example of a test signal generated by analog conversion is the waveform shown in FIG.

  FIG. 5 is a graph showing the time change of the electric power of the electric signal of which the reflected light is converted by the light receiving element provided in the ICR 16. The reflected light includes light returned after the inspection signal is reflected at the failure location (hereinafter referred to as “returned light”), Rayleigh scattered light, Brillouin scattered light, and Raman scattered light. The DSP 10 arranges the power of the reflected pulses in time series.

  FIG. 6 is a diagram showing a specific example of an outline of analysis processing performed by the DSP 10. The graph shown in FIG. 6 is a graph obtained by differentiating the graph showing the relationship between time and power shown in FIG. The horizontal axis of the graph shown in FIG. 6 represents time, and the vertical axis represents the differential value of power. In the graph of FIG. 6, a peak occurs at a point where the change is large. The DSP 10 estimates a problem location based on a singular point in a time-series power change.

  FIG. 7 is a functional block diagram showing the configuration of the DSP 10 according to the embodiment of the present invention, in which only functional blocks related to the OTDR mode operation are extracted and shown. The DSP 10 shown in the figure includes an FFT (Fast Fourier Transform) unit 101, a wavelength dispersion compensation unit 102, a control unit 103, an IFFT (Inverse Fast Fourier Transform) unit 104, a return light detection unit 105, and an analysis unit 106.

  The FFT unit 101 performs FFT on the digital electric signal input from the ADC 17. The chromatic dispersion compensation unit 102 performs chromatic dispersion compensation processing on the FFT result in accordance with control by the control unit 103. The control unit 103 determines the chromatic dispersion amount based on the digital electrical signal input from the ADC 17. The control unit 103 outputs a control signal to the chromatic dispersion compensation unit 102 so as to execute the chromatic dispersion compensation process based on the determined chromatic dispersion amount. The IFFT unit 104 performs IFFT on the electrical signal that has been subjected to chromatic dispersion compensation by the chromatic dispersion compensation unit 102. The return light detection unit 105 detects an electrical signal derived from the return light (hereinafter referred to as “return light signal”) based on the result of the IFFT. The analysis unit 106 detects the presence / absence of a failure location and the failure location based on the return optical signal.

  Next, details of the process performed by the control unit 103 will be described. When the chromatic dispersion compensation unit 102 compensates for chromatic dispersion, it is difficult to precisely determine how much compensation should be performed because it is unclear at which point the return light is maximized. Therefore, the control unit 103 in the present embodiment determines an appropriate amount of chromatic dispersion compensation by using one of the following two algorithms. Which algorithm is used may be determined in advance in the DSP 10, or may be appropriately selected based on a predetermined criterion.

1. First Algorithm In the first algorithm, the control unit 103 searches for a compensation value that maximizes the sensitivity of the return light by sweeping the wavelength dispersion value. The control unit 103 determines an appropriate wavelength compensation amount based on the result of the search process. Specifically, the control unit 103 performs processing as follows.

  First, the control unit 103 controls generation of a pulse signal such that pulse light of a predetermined time width is output as an inspection signal. It is desirable that the time width of the pulsed light output first is wider (thicker) than the time width of the pulsed light used in the subsequent processing. The control unit 103 controls the chromatic dispersion compensation unit 102 so that chromatic dispersion compensation is not performed in the process using the pulse light output first. The analysis unit 106 detects a failure point based on the return light signal detected under such control. The control unit 103 determines the chromatic dispersion compensation amount according to the estimated value of the distance from the own apparatus to the detected failure point. Next, the control unit 103 controls generation of a pulse signal such that pulse light having a narrower (thin) time width than that of the previous pulse light is output as an inspection signal. The control unit 103 controls the chromatic dispersion compensation unit 102 to perform processing using the chromatic dispersion compensation amount determined based on the OTDR processing using the previous pulse light. In this way, the time width of the pulsed light is made narrower than the previous process, and the failure location is detected using the chromatic dispersion compensation amount determined by the previous process. . The control unit 103 ends the above process when the repeated end condition is satisfied. Then, the control unit 103 determines the amount of chromatic dispersion obtained when the termination condition of repetition is satisfied as an appropriate amount of chromatic dispersion compensation. The failure location may be detected based on the detection result of the OTDR process using the chromatic dispersion compensation amount obtained in this manner. Moreover, the detection result by the OTDR process performed when the end condition is satisfied may be used as the detection result of the failure part. The termination condition of the repetition may be, for example, that the process is repeatedly executed a predetermined number of repetitions. The termination condition of the repetition may be, for example, that a change in value of the obtained estimated value or the like (change from the previous process) is smaller than a predetermined threshold. The end condition of repetition may be another condition.

2. Second Algorithm In the second algorithm, the control unit 103 searches for a compensation value that maximizes the sensitivity of the return light by sweeping the chromatic dispersion value by a method different from that of the first algorithm. The control unit 103 determines an appropriate wavelength compensation amount based on the result of the search process. Specifically, the control unit 103 performs processing as follows.

  First, the control unit 103 controls generation of a pulse signal such that pulse light of a predetermined time width set to be used in OTDR processing is output as an inspection signal. In the second algorithm, unlike the first algorithm, the time width of the pulse signal does not change. The control unit 103 controls the chromatic dispersion compensation unit 102 so that chromatic dispersion compensation is not performed in the process using the pulse light output first. The analysis unit 106 detects a failure point based on the return light signal detected under such control. The control unit 103 controls the chromatic dispersion compensation unit 102 so that the chromatic dispersion compensation amount is different from the chromatic dispersion compensation amount used in the previous OTDR process. As described above, detection of a failure point is repeatedly performed using different chromatic dispersion compensation amounts. The control unit 103 ends the above process when the repetition end condition is satisfied. Then, the control unit 103 determines the chromatic dispersion amount obtained when the repetition end condition is satisfied as an appropriate chromatic dispersion compensation amount. The failure location may be detected based on the detection result by the OTDR process using the chromatic dispersion compensation amount thus obtained. The termination condition of the repetition may be, for example, that the process is repeatedly executed a predetermined number of repetitions. The end condition of repetition may be another condition.

  Note that the dispersion compensation amount may be determined by means different from the two algorithms described above. For example, when the approximate chromatic dispersion value is specified in advance, the control unit 103 controls the chromatic dispersion compensation unit 102 using the chromatic dispersion compensation amount obtained based on the specified chromatic dispersion value. May be. For example, the control unit 103 may estimate the chromatic dispersion amount by executing an existing chromatic dispersion estimation process, and may control the chromatic dispersion compensation unit 102 using the chromatic dispersion compensation amount obtained based on the estimation result. . As a specific example of such existing wavelength dispersion estimation processing, there is a technique described in Japanese Patent Application Publication No. 2015-141658.

Next, the process performed by the analysis unit 106 will be described. Among the values used in the analysis processing, the analysis unit 106 calculates the time (return time: Tr) required for the pulse light to be reflected at the failure point and to return to the ADC 17 by using the following equation.

  In Expression 1, Tdet represents the detection time required from when the pulse light is reflected at the failure point to when it is detected by the return light detection unit 105. Tcal represents the processing time required for the chromatic dispersion compensation processing executed in the chromatic dispersion compensation unit 102. The processing time Tcal may be set in the analysis unit 106 as a fixed value in advance.

  The analysis unit 106 determines a failure location using the return time Tr obtained by the above-described processing. Note that any existing technique may be applied to the technique for determining the failure location using the return time Tr.

  FIG. 8 is a diagram illustrating an inspection signal adjustment method for improving measurement quality. As shown in FIG. 8, in order to improve the measurement quality in an inspection using a pulse inspection signal, there is a method of increasing the power.

  The optical transceivers 1, 1a, 1b are arranged, for example, as OTDRs in a WDM (Wavelength Division Multiplex). An optical transceiver arranged as an OTDR may measure a vacant wavelength fixedly or may rotate and measure a plurality of vacant wavelengths. When measuring a plurality of wavelengths by rotation, one optical transceiver may measure with different wavelengths, or each of the plurality of optical transceivers may measure at a fixed different wavelength. Also, in order to be able to measure not only the vacant wavelength but also all the wavelengths used for WDM, it is possible to rotate and measure the signal transmitted at the relevant wavelength while switching.

  9 and 10 are diagrams showing an example of application of the optical transceiver of this embodiment to WDM. 9 and 10, the optical transceiver 1 is shown as a specific example of the optical transceiver of the present embodiment. However, instead of part or all of the optical transceivers 1, an optical transceiver 1 a or an optical transceiver 1 b may be applied. FIG. 9 is a diagram illustrating an example in which measurement is performed with one optical transceiver. As shown in the figure, a plurality of optical transceivers 1 are connected to the wavelength multiplexer / demultiplexer 60. The plurality of optical transceivers 1 in the transceiver mode transmit and receive light of different wavelengths. The wavelength multiplexer / demultiplexer 60 is, for example, an AWG (arrayed waveguide grating, arrayed waveguide grating) or a WSS (wavelength selective switch). The wavelength multiplexer / demultiplexer 60 multiplexes the optical signals of different wavelengths input from the plurality of optical transceivers 1 and outputs the multiplexed signal to the transmission path. The wavelength multiplexer / demultiplexer 60 receives an optical signal that has been wavelength-multiplexed from the transmission line, demultiplexes the input optical signal into an optical signal of each wavelength, and outputs the optical signal to each of the plurality of optical transceivers 1. At the time of measurement, one optical transceiver 1 switches from the transceiver mode to the OTDR mode and operates. A conventional optical transceiver may be used instead of the optical transceiver 1 that does not perform measurement.

In the configuration shown in the figure, the optical transceiver 1 in the OTDR mode measures a vacant fixed wavelength. Alternatively, the OTDR mode optical transceiver 1 measures and monitors an empty wavelength group that is not used by the transceiver mode optical transceiver 1 while rotating. Also, while the OTDR mode optical transceiver 1 changes the wavelength to sweep as λ ₁ , λ ₂ , λ ₃ , ..., the free wavelength group and transceiver of the transceiver mode optical transceiver 1 are not used All wavelength groups combined with the wavelength groups used by the optical transceiver 1 in the mode may be measured and monitored by one unit. While the optical transceiver 1 in the OTDR mode is performing a measurement, the optical transceiver 1 in the transceiver mode is prevented from using the wavelength being measured.

  FIG. 10 is a diagram illustrating an example in which measurement is performed by a plurality of optical transceivers. 10, parts that are the same as the parts shown in FIG. 9 are given the same reference numerals, and descriptions thereof will be omitted. In FIG. 10, a plurality of optical transceivers 1 are connected to the wavelength multiplexer / demultiplexer 60, and at the time of measurement, the plurality of optical transceivers 1 are switched from the transceiver mode to the OTDR mode. A conventional optical transceiver may be used instead of the optical transceiver 1 that does not perform measurement. The plurality of optical transceivers 1 in the transceiver mode transmit and receive light of different wavelengths. In the configuration shown in FIG. 10, the plurality of optical transceivers 1 in the OTDR mode rotate and measure free fixed wavelengths in the OTDR mode. Alternatively, each of the plurality of optical transceivers 1 in the OTDR mode may measure a fixed empty wavelength different from that of the other optical transceivers 1 in the OTDR mode. In addition, when each optical transceiver 1 in the OTDR mode changes the wavelength, all the wavelength groups including the free wavelength group and the wavelength group used by the optical transceiver 1 in the transceiver mode are combined into a plurality of OTDR modes. It may be measured and monitored by the optical transceiver 1.

  11 and 12 are diagrams showing the relationship between the pulse width of pulsed light and power. FIG. 11 is a diagram showing changes in pulse width and power when pulse light with a wide frequency band (pulse light with a narrow time interval) is used. FIG. 12 is a diagram showing a change in pulse width and power when pulse light with a narrow frequency band (pulse light with a wide time interval) is used. As can be seen from FIGS. 11 and 12, when the pulse width (time interval) is narrow, the effect of waveform spreading due to wavelength dispersion is large. On the other hand, when the pulse width (time interval) is wide, the waveform spreading effect due to wavelength dispersion is small. The peak power decreases as the pulse width widens. For this reason, the sensitivity of the return light is lowered, and the resolution may be lowered.

  According to the embodiment described above, the chromatic dispersion compensation unit 102 of the DSP 10 executes the chromatic dispersion compensation process on the reflected light. Therefore, it becomes possible to detect a fault location using pulsed light having a narrower frequency band. As a result, it is possible to suppress the reduction in resolution.

  Further, when the analysis unit 106 of the DSP 10 acquires the value of the return time Tr used when the failure part analysis process is performed, the processing time Tcal required for the chromatic dispersion compensation process by the chromatic dispersion compensation unit 102 is excluded. . For this reason, it is possible to suppress a decrease in accuracy due to the execution of the chromatic dispersion compensation process.

  Further, the controller 103 determines an appropriate amount of chromatic dispersion compensation. Therefore, more appropriate chromatic dispersion compensation processing can be performed. As a result, it is possible to detect a failure point using a narrower pulse light, and it is possible to suppress a decrease in resolution.

  One or more first optical transceivers (for example, optical transceivers) which are the above-mentioned optical transceivers having the function of transmitting and receiving optical signals and the function of evaluating the characteristics of optical fibers in optical communications in an optical communication system such as WDM. The transceiver 1) may include one or more second optical transceivers (for example, the optical transceiver 1 or a conventional optical transceiver) that are optical transceivers for transmitting and receiving optical signals, and a multiplexer / demultiplexer. The multiplexer / demultiplexer outputs a wavelength-multiplexed signal obtained by multiplexing the optical signals of different wavelengths output from the first optical transceiver and the second optical transceiver. The multiplexer / demultiplexer receives the wavelength-multiplexed optical signal, demultiplexes the received optical signal, and outputs the demultiplexed optical signal to the first optical transceiver and the second optical transceiver.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within the scope of the present invention.

  It can be used for an optical communication system.

DESCRIPTION OF SYMBOLS 1 ... Optical transceiver, 10 ... DSP, 11 ... DAC, 101 ... FFT part, 102 ... Wavelength dispersion compensation part, 103 ... Control part, 104 ... IFFT part, 105 ... Return light detection part, 106 ... Analysis part, 12 ... LD 13 ... IQM, 14 ... circulator, 15 ... SW, 16 ... ICR, 17 ... ADC, 21 ... ATT, 22 ... ATT, 23 ... coupler, 31 ... coupler, 32 ... attenuator, 33 ... attenuator, 34 ... coupler 60: Wavelength multiplexer / demultiplexer

Claims (5)

A modulator for outputting pulsed light as a test signal to a transmission path;
A conversion unit that generates an electrical signal by converting reflected light that is light generated by reflection or scattering of the pulsed light in the transmission path;
A chromatic dispersion compensation unit that performs chromatic dispersion compensation on the electric signal;
In the electrical signal that has been subjected to chromatic dispersion compensation, a return light detection unit that detects an electrical signal derived from return light caused by reflection of the pulsed light at a failure location of the transmission path; and
An analysis unit that determines the failure location based on an electrical signal derived from the return light;
An optical transceiver comprising:   The analysis unit acquires time excluding time required for processing of chromatic dispersion compensation in the chromatic dispersion compensation unit when acquiring the time until the return light reaches its own device. The optical transceiver as described.   The optical transmitter-receiver according to claim 1 or 2, further comprising: a control unit that determines the compensation amount of the chromatic dispersion compensation in the chromatic dispersion compensation unit.   The control unit performs control so that pulse light with a narrow pulse width is output in order in the modulation unit, and determines the compensation amount according to a failure location estimated based on each pulse light. The optical transceiver described in 1.   The control unit controls the chromatic dispersion compensation unit so that the chromatic dispersion compensation is performed with a plurality of different compensation amounts, and determines the compensation amount according to a result of each chromatic dispersion compensation. Optical transceiver.

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