Optical fiber measurement system and method

Abstract

This optical fiber measurement system comprises: an incident light transmitting unit 11 that transmits pulsed light into a plurality of optical fibers; circulators 31, 32 that transfer scattered light from the plurality of optical fibers to a scattered light receiving unit 12; and a transmitting unit switch 20 that is interposed between the incident light transmitting unit 11 and the circulators 31, 32, and that switches a connection between the incident light transmitting unit 11 and the plurality of optical fibers such that an optical transmission path for transmitting the pulsed light is formed between the incident light transmitting unit 11 and any one of the plurality of optical fibers.

Description

Optical fiber measurement system and method

[0001] The present disclosure relates to a technique for reducing the unmeasurable time of an optical fiber.

[0002] 2. Description of the Related Art Conventionally, an optical fiber sensing device known as an OTDR (Optical Time-Domain Reflectometer) is one that inputs pulsed light into an optical fiber and extracts scattered light.

[0003] In OTDR measurements, if a switch capable of switching between multiple optical fiber cores is used, scattered light from multiple cores can be measured with a single measuring instrument. For example, Non-Patent Document 1 discloses a phase OTDR that measures scattered light from multiple cores laid in a plane while switching between the cores using an optical switch, thereby performing planar sensing. Non-Patent Document 2 also discloses an optical switch capable of switching between cores.

[0004] Specifically, in order to switch between multiple cores for measurement, it is conceivable to provide a switch 20A between an OTDR measurement device 10A and multiple cores A and B, as shown in Fig. 1. Fig. 1 shows an example in which two cores A and B are switched between by the switch 20A, but in reality, it is required to switch between more cores.

[0005] 1, to measure scattered light while switching the connection of switch 20A from core wire A to core wire B, the following steps (1) to (4) must be taken: (1) Inject the final pulse of light into core wire A. (2) All of the scattered light generated from the final pulse of light passes through the circulator. (3) Operate switch 20A so that the connection of the port on the right side of the figure switches from core wire A to core wire B. (4) After switching to core wire B is complete, inject the first pulse of light into core wire B.

[0006] 1, it is necessary to wait until all scattered light from core wire A has passed through the circulator before switching from core wire A to core wire B. This causes a period of time during which measurement is not possible (dead time) corresponding to the switching time of the switch, as shown in Fig. 2. This period of time during which measurement is not possible corresponding to the switching time of the switch affects the efficiency of measurement.

[0007] Myeonggyun Kye, et al. "A Surveillance System of Fiber-Optic Cables With Multi-Channel DAS and CNN." IEEE PHOTONICS TECHNOLOGY LETTERS, vol. 33, no. 15, pp. 753-756, 2021. Current Status and Future of Optical Switches, Naoya Uchida, Optics, Vol. 21, No. 8, pp. 510-515, August 1992.

[0008] Therefore, an object of the present disclosure is to provide an optical fiber measurement system that can suppress dead time.

[0009] In order to achieve the above object, the optical fiber measurement system and method disclosed herein employ a technique in which a first switching unit that switches the connection between the transmitting unit and multiple optical fibers is interposed between the transmitting unit and the transmitting unit.

[0010] Specifically, the optical fiber measurement system of the present disclosure includes a transmitter that transmits pulsed light to a plurality of optical fibers; a transmitter that transmits scattered light from the plurality of optical fibers to a light receiver; and a first switching unit that is interposed between the transmitter and the transmitter and switches the connection between the transmitter and the plurality of optical fibers so that an optical transmission path for transmitting the pulsed light is formed between the transmitter and any one of the plurality of optical fibers.

[0011] The optical fiber measurement method of the present disclosure also includes: a transmitter transmitting pulsed light to a plurality of optical fibers; a transmitter transmitting scattered light from the plurality of optical fibers to a light receiving unit; and a switching unit interposed between the transmitter and the transmitter switching a connection between the transmitter and the plurality of optical fibers so that an optical transmission path for transmitting the pulsed light is formed between the transmitter and any one of the plurality of optical fibers.

[0012] With this, since the first switching unit is located before the transmission unit in the transmission path of the pulsed light, it is not necessary to wait for the scattered light from the optical fiber before switching to pass through the transmission unit before switching the connection between the transmitter and the multiple optical fibers, which makes it possible to reduce dead time and perform efficient measurements.

[0013] The transmission unit may also include a plurality of circulators corresponding to the plurality of optical fibers, the first switching unit may start switching the connection between the transmission unit and the plurality of optical fibers before the scattered light in the optical fiber before switching passes through the circulator corresponding to the optical fiber before switching, and a second switching unit may be provided which includes a plurality of connection ports corresponding to the plurality of circulators and switches the connection between the plurality of circulators and the plurality of optical fibers so that an optical transmission path for the light receiving unit to receive the scattered light is formed between any of the plurality of circulators and the light receiving unit, and starts switching the connection between the plurality of circulators and the plurality of optical fibers before the scattered light in the optical fiber before switching passes through the circulator corresponding to the optical fiber before switching.

[0014] This allows the occurrence of dead time to be suppressed since the time for switching the optical fiber and the time for measuring the scattered light overlap.

[0015] The light receiving section may include a two-input / two-output coupler, and scattered light from different circulators may be incident on each of two inputs of the two-input / two-output coupler.

[0016] This makes it possible to suppress the occurrence of unnecessary optical loss other than insertion loss.

[0017] The above disclosures can be combined as much as possible.

[0018] According to the optical fiber measurement system and method of the present disclosure, it is possible to suppress dead time, thereby enabling efficient measurement.

[0019] FIG. 1 is a diagram illustrating the configuration of a related OTDR measurement device and a switch. FIG. 2 is a diagram illustrating the occurrence of dead time associated with switching a switch. FIG. 3 is a diagram illustrating an overview of a switch used in the present disclosure, and definitions of various terms related to response speed. FIG. 4 is a diagram illustrating the configuration of an optical fiber measurement system. FIG. 5 is a flowchart illustrating the procedure for switching a measurement core wire. FIG. 6 is a timing chart of the switching procedure. FIG. 7 is a diagram illustrating the generation of noise. FIG. 8 is a diagram illustrating the connection state between a receiving unit switch and each core wire. FIG. 9 is a flowchart illustrating the procedure for switching a measurement core wire. FIG. 10 is a timing chart of the switching procedure. FIG. 11 is a diagram illustrating the configuration of a scattered light receiving unit according to a fourth embodiment of the present disclosure. FIG. 12 is a diagram illustrating switching of another switch.

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0021] (Outline of Switch Configuration and Definitions of Various Terms Related to Response Speed) First, with reference to FIG. 3 , an outline of the configuration of a switch used in the present disclosure and definitions of various terms related to response speed used in the present disclosure will be described. FIG. 3(A) is a schematic diagram of a switch used in the present disclosure. The switch is a 1×2 optical switch having one port on the left side of the figure and two ports on the right side. One optical fiber is connected to the left port of the switch, and two optical fibers are connected to the right port of the switch. In the following description, the optical fibers are referred to as "core wires." Furthermore, one of the two core wires directly or indirectly connected to the right port of the switch is referred to as "core wire A," and the other is referred to as "core wire B." The switch switches so that incident light from the core wire connected to the left port is output as transmitted light to either core wire A or core wire B.

[0022] Figure 3(B) is a graph showing the transmitted light intensity measured with time on the horizontal axis by connecting a device (for example, a photodiode) that can measure light intensity to core wire A and core wire B. As shown in Figure 3(A), when the right port of the switch is switched from the state where it is connected to core wire A to the state where it is connected to core wire B, the optical signal moves from core wire A to core wire B. Figure 3(B) shows that as the optical signal moves from core wire A to core wire B in this way, the optical intensity of core wire A decreases and the optical intensity of core wire B increases.

[0023] The "switching time W" shown in Fig. 3(B) corresponds to the time required to switch the core wires, and if the time L for measuring the scattered light returning from core wire A (which corresponds to the duration of the scattered light from core wire A and will be referred to as "duration L" hereafter) is equal to or longer than the switching time W, the switching time W is defined as the time from the start of the operation required to switch the core wires until the light intensity of core wire B has risen sufficiently (see Figs. 6(A) and 10(A)). On the other hand, if the time required to switch the core wires is longer than duration L, the switching time W is defined as the time from the incidence of the final pulse light on core wire A until the light intensity of core wire B has risen sufficiently (see Figs. 6(B) and 10(B)).

[0024] "Time w1" is defined as the time from when the light intensity of core wire A starts to drop until the light intensity of core wire A has dropped sufficiently. This time w1 is also considered as the time required for switching when measuring by distinguishing scattered light. Note that time w1 corresponds to the time during which "noise" occurs in the third embodiment. "Time w2" is defined as the time during which no light intensity is observed in either core wire A or core wire B. In addition, in this disclosure, the time during which measurement is not possible corresponding to various switching times is called "dead time."

[0025] In the second embodiment described below, it is assumed that the scattered light drops suddenly when the switch is switched, so the explanation will be given using only the switching time W, without time w1. On the other hand, in the third embodiment, it is assumed that the scattered light drops gradually when the switch is switched, so the explanation will be given based on both time w1 and the switching time W.

[0026] The present disclosure can also be applied to other types of switches that operate differently from the above, because the switching time W occurs regardless of the type of switch, and the problem of reducing the dead time is common to all types of switches.

[0027] First Embodiment An optical fiber measurement system according to a first embodiment of the present disclosure will be described with reference to FIG. 4. As shown in the figure, the optical fiber measurement system mainly includes an OTDR (Optical Time-Domain Reflectometer) measurement device 10 having an incident light transmitting unit 11 and a scattered light receiving unit 12, a transmitter switch 20, two circulators 31 and 32, and two receiver switches 41 and 42. The incident light transmitting unit 11 functions as a "transmitter." The scattered light receiving unit 12 functions as a "receiver." The circulators 31 and 32 function as a "transmitter." The transmitter switch 20 functions as a "first switching unit." The receiver switches 41 and 42 function as "second switching units." The receiver switches 41 and 42 also function as "connection ports."

[0028] In this embodiment, the switches are divided into a transmitter switch 20 and two receiver switches 41 and 42, which are operated independently. In addition, by locating the transmitter switch 20 before the circulators 31 and 32, the port on the right side of the transmitter switch 20 is switched to the next core wire to be measured (core wire B in this case) without waiting for the reception of scattered light.

[0029] Furthermore, in this embodiment, a receiver switch 41 is provided to control the connection between core wire A and circulator 31, and a receiver switch 42 is provided to control the connection between core wire B and circulator 32. That is, in this embodiment, the transmitter switch 20 and various core wires are connected via the circulator and the receiver switch. In this embodiment, the receiver switch 42 starts operating in advance to connect core wire B and circulator 32 before all of the scattered light from core wire A passes through circulator 31, thereby reducing the dead time resulting from the switching time W.

[0030] Specifically, the optical fiber measurement system of the present disclosure comprises an incident light transmitting unit 11 that transmits pulsed light to multiple optical fibers, circulators 31, 32 that transmit scattered light from the multiple optical fibers to a scattered light receiving unit 12, and a transmitting unit switch 20 that is interposed between the incident light transmitting unit 11 and the circulators 31, 32 and switches the connection between the incident light transmitting unit 11 and the multiple optical fibers so that an optical transmission path for transmitting pulsed light is formed between the incident light transmitting unit 11 and any one of the multiple optical fibers.

[0031] The transmitter switch 20 may also include receiver switches 41, 42 which are configured to start switching the connections between the incident light transmitter 11 and the multiple optical fibers before the scattered light in the optical fiber before switching passes through the circulator 31 corresponding to the optical fiber before switching, and to switch the connections between the multiple circulators and the multiple optical fibers so that an optical transmission path is formed between any of the multiple circulators and the scattered light receiver 12 for receiving scattered light, and which start switching the connections between the multiple circulators and the multiple optical fibers before the scattered light in the optical fiber before switching passes through the circulator 31 corresponding to the optical fiber before switching.

[0032] Unlike the case shown in the figure, only one receiver switch having multiple internal switching mechanisms (ports) may be provided. Specifically, one of the multiple ports may be configured to control the connection between core wire A and circulator 31, and another of the multiple ports may be configured to control the connection between core wire B and circulator 32.

[0033] Also, unlike the case shown in the figure, the receiver switches 41 and 42 may be provided between the circulators 31 and 32 and the scattered light receiver 12, respectively.

[0034] The configuration of this embodiment can also be applied when the number of core wires to be measured is three or more, because during measurement, it is only necessary to consider the connection between the measurement device and the core wire currently being measured, and the connection between the measurement device and the next core wire to be measured.

[0035] As shown in the figure, the OTDR measurement device 10 includes an incident light transmitter 11 and a scattered light receiver 12. The incident light transmitter 11 emits pulsed light toward the transmitter switch 20.

[0036] The scattered light receiving section 12 is an example of a light receiving section when the OTDR measurement device employs a direct detection configuration among phase OTDR configurations. In a direct detection configuration, two scattered light signals are separated by a coupler and used. This allows phase OTDR measurements to be performed without incurring additional optical loss.

[0037] The scattered light receiving unit 12 includes a conversion unit 121, a photodetector 122, and a phase calculation unit 123. The conversion unit 121 includes a two-input / two-output coupler and a three-input / three-output coupler. The scattered light from circulator 31 and the scattered light from circulator 32 are input to each of the two inputs of the two-input / two-output coupler. The conversion unit 121 then receives and combines the scattered light from circulators 31 and 32, and then splits it into multiple paths. The photodetector 122 receives the optical signal from the conversion unit 121 and converts it into an electrical signal. The phase calculation unit 123 performs calculations based on the electrical signal from the photodetector.

[0038] In this way, by providing two inputs to the coupler, with the signal from circulator 31 input to one of the two inputs and the signal from circulator 32 input to the other, and using the two resulting outputs to perform direct detection phase measurement, it is possible to suppress the occurrence of unnecessary optical loss other than insertion loss.

[0039] Second Embodiment [Flowchart] Based on the configuration of the first embodiment, a procedure for an optical fiber measurement system to switch the measurement core wire from core wire A to core wire B will be described as a second embodiment with reference to the flowchart in Fig. 5. Note that in this embodiment, the procedure will be described on the premise that, when switching from core wire A to core wire B, scattered light from core wire A is received by scattered light receiving unit 12. In addition, in the procedure shown in Fig. 5, the incident light transmitting unit 11, transmitting unit switch 20, circulators 31, 32, and receiving unit switches 41, 42 operate.

[0040] First, in step S1-A, the incident light transmitting unit 11 transmits the final pulse of light to core wire A. In parallel with step S1-A, or immediately before the final pulse of light is transmitted to core wire A, in step S1-B, core wire B is connected to the receiving unit switch 42. Step S1-B is a preparatory operation for switching measurement from core wire A to core wire B. At this stage, no pulse of light is transmitted to core wire B, and the pulse of light is emitted from the incident light transmitting unit 11 to core wire A via the circulator 31.

[0041] Next, in step S2, the connection of the right port of the transmitter switch 20 is switched from the circulator 31 to the circulator 32. As a result, the connection of the right port of the transmitter switch 20 via the circulator and the receiver switch is switched from core wire A to core wire B so that pulsed light is emitted to core wire B via the circulator 32.

[0042] Since the incident light transmitting unit 11 emits pulsed light to the core wire A until immediately before switching from the core wire A to the core wire B, scattered light corresponding to the pulsed light returns to the core wire A. This scattered light needs to be measured, and in this embodiment, the scattered light is received by the scattered light receiving unit 12 using the circulator 31, so that the measurement is performed by the scattered light receiving unit 12.

[0043] Next, the timing of emitting pulsed light to core wire B will be described. In step S3, immediately after the scattered light from core wire A passes through the circulator 31, the incident light transmitter 11 emits the first pulsed light for measuring core wire B. The pulsed light is incident on core wire B via the transmitter switch 20, the circulator 32, and the receiver switch 42.

[0044] This method makes it possible to measure the final scattered light from core wire A while seamlessly (without dead time) emitting pulsed light to core wire B. Note that the process of switching the transmitter switch 20 as described above may be performed by an actuator that receives an instruction from the OTDR measurement device 10.

[0045] [Timing Chart] Next, with reference to Fig. 6, a timing chart for the case where the procedure in Fig. 5 is followed will be described. In the timing chart of Fig. 6, the horizontal axis represents measurement time. In the figure, scattered light from core fiber A is shown as a filled-in trapezoidal figure, and scattered light from core fiber B is shown as a hatched trapezoidal figure extending from the upper left to the lower right. The scattered light from core fiber A is the last and shows one pulse. The downward slope of each scattered light indicates that the intensity of the scattered light decreases over time. This decrease in scattered light intensity over time is due to loss in the optical fiber.

[0046] 6 shows two timing charts, (A) and (B), depending on whether or not dead time occurs. Specifically, whether or not dead time occurs is determined by the balance between the time L (duration L) for measuring scattered light returning from the core wire A and the switching time W. In this embodiment, the time required to complete both step S1-B and step S2 corresponds to the switching time W.

[0047] 6A shows a case where the duration L of scattered light from core wire A is equal to or longer than the switching time W (L≧W). In order to prevent the occurrence of dead time, it is necessary to complete both step S1-B and step S2 at the timing when pulsed light is emitted to core wire B (the timing of step S3). In other words, it is necessary to start both steps S1-B and S2 by timing P, which is the switching time W before the timing of step S3.

[0048] 6A, since the duration L is equal to or longer than the switching time W, the dead time can be reduced by starting step S1-B and step S2 at the same time that the incident light transmitting unit 11 emits the final pulsed light to the core wire A. In step S1-B, the receiving unit switch 42 can be operated independently of the emission of the pulsed light to the core wire A. Therefore, it is sufficient to operate step S1-B at a stage earlier than timing P, and the procedure may proceed in the order of step S1-B and step S2, unlike that shown in FIG.

[0049] As described above, by matching the timing at which the measurement of scattered light from the core wire A ends with the time W required for switching, it is possible to eliminate the dead time.

[0050] 6(B) shows the case where the duration L of scattered light from core wire A is shorter than the switching time W (L<W). In this case, dead time occurs. This is because the switching from core wire A to core wire B is not complete (switching time W has not yet elapsed) even after the measurement of scattered light from core wire A has finished (duration L has elapsed). This is because step S2, in which circulator 31 is switched to circulator 32, must be performed after the final pulse of light has been emitted to core wire A. As a result, measurement of scattered light from core wire B starts with a delay, and so dead time exists. However, compared to the prior art, the switching time W and the scattered light measurement time overlap, which has the effect of reducing dead time.

[0051] [Mechanism for matching switching time and duration] As described above, the dead time can be more effectively suppressed by matching the switching time W and the duration L of scattered light (W=L), or by making the switching time W longer than the duration L (W>L). Therefore, a method for making the switching time W equal to or longer than the duration L will be considered.

[0052] First, the switching time W is determined by the specifications of the transmitter switch 20. Therefore, the switching time W can be determined from the specifications table of the transmitter switch 20.

[0053] On the other hand, the duration L is determined by the fiber length of the optical fiber core. If the fiber length is F, the refractive index at the center wavelength of the probe light in a vacuum is n, and the high speed in a vacuum is c, the duration L satisfies the following: L = 2nF / c

[0054] However, it is necessary to measure the ghost component. Alternatively, if the ghost component cannot be ignored, the duration must be considered as follows: L = 4 nF / c. The ghost component is the scattered light generated when the probe light is reflected at the far end and travels in the opposite direction.

[0055] By repeatedly comparing and verifying the switching time W and duration L obtained from the above and making the duration L of scattered light from core wire A equal to or greater than the switching time W, it is possible to reduce or completely eliminate the dead time. The verified duration L and switching time W may be stored as data in the OTDR measurement device 10 and used for processing. In particular, in step S3 of the flowchart in Figure 5, the incident light transmitter 11 may emit the first pulse light to measure core wire B based on the data on the duration L and switching time W stored in the OTDR measurement device 10.

[0056] For example, if the core wire A can be preliminarily measured before the switch is installed, the duration L and the switching time W can be determined by the following procedure.

[0057] Specifically, first, the length of core wire A is measured and duration L is calculated. The length of core wire A can be measured by sending pulsed light from incident light transmitter 11 to core wire A, receiving scattered light from core wire A via a circulator with scattered light receiver 12, and directly measuring duration L of the scattered light signal. Alternatively, duration L can be measured using a separate OTDR device.

[0058] The OTDR measurement device 10 is constructed using a switch with specifications that satisfy L≧W for the duration L measured or calculated using the method described above.

[0059] (Third Embodiment) A third embodiment of the present disclosure will be described with reference to Figs. 7 to 10. In the second embodiment described above, a model was assumed in which the light intensity of scattered light from the core wire A drops sharply (vertically) over a certain measurement time. However, in a realistic measurement, the light intensity of scattered light does not drop vertically. From experience, the light intensity of scattered light decreases with a certain slope.

[0060] FIG. 7 shows pulse patterns of three optical signals. The upper part of FIG. 7 shows a pattern in which the light intensity of scattered light, which is the premise of the second embodiment, drops vertically over a certain measurement time. However, in reality, such a vertical drop in light intensity is unlikely, and instead decreases with a certain slope, as shown in the middle part of FIG. 7. In this disclosure, the portion that gradually decreases with a certain slope at the end of the measurement time is defined as "noise." The purpose of this embodiment is to provide a realistic model that takes the noise time into account while reducing the noise, as shown in the lower part of FIG. 7.

[0061] There are two possible cases where noise remains: (1) When the probe light is reflected at the far end and travels in the opposite direction, and the ghost component, which is scattered light generated in the process, has a high intensity, the ghost component becomes noise. (2) When you do not want to measure the entire fiber section of core wire A, but want to measure only a certain section from the input end, the scattered light from the far end section, which is not intended to be visualized, becomes noise.

[0062] [Noise Removal Method] In this embodiment, a method for removing noise is employed in which the connection of the receiver switch is switched from the core wire that was previously measured to a core wire that is free of noise. Specifically, as shown in FIG. 8 , the connection of the right port of the 1×2 receiver switch 41 is switched from core wire A, which was previously measured, to core wire C. Since no equipment such as a transmitter is connected to core wire C, no optical signal propagates therethrough. Therefore, there is no noise generated from the optical signal. Furthermore, the edge of core wire C is pre-treated, for example, to have a non-reflective end, to prevent noise from occurring in the optical fiber.

[0063] [Flowchart] In the third embodiment, the procedure when the optical fiber measurement system switches the measurement core wire from core wire A to core wire B will be described with reference to the flowchart in Fig. 9. Since the procedure is basically the same as the procedure flow in the second embodiment (Fig. 5), only the differences will be described.

[0064] Specifically, in the third embodiment, step S4 related to the receiver switch 41 is executed before step S3. In step S4, the connection of the right port of the receiver switch 41 is switched from core A to core B, which is free of noise. As described above, no equipment such as a transmitter is connected to core C, so no optical signal is propagating therethrough. Therefore, there is no noise generated from the optical signal, and so noise can be reduced by switching from core A to core C. The noise is reduced as shown in the pulses in the lower part of Figure 7.

[0065] This method can reduce the continuous noise. However, it is difficult to completely eliminate the noise, and the time w1 required for the remaining noise to disappear must be included in the switching time. The effectiveness of eliminating the noise and the time w1 required depend greatly on the switching speed and switching time of the receiver switch 41. Therefore, the time w1 can be estimated by understanding the specifications (switching speed, switching time) of the receiver switch 41 used. Note that the process of switching the receiver switch 41 as described above may be performed by an actuator receiving instructions from the OTDR measurement device 10.

[0066] Next, a timing chart for the third embodiment when the procedure of Fig. 9 is followed will be described with reference to Fig. 10. The timing chart for the third embodiment is basically the same as the timing chart for the second embodiment (Fig. 6), and therefore only differences will be described.

[0067] Specifically, in the third embodiment, in step S4, the connection of the receiver switch 41 is switched from core A to noise-free core C, and it is necessary to take into consideration the time w1 required for the remaining noise generated at that time to decrease. In other words, in this embodiment, the switching time W corresponds to the time required to complete both step S1-B and step S2 plus time w1.

[0068] 10A shows a case where the time obtained by adding the time w1 to the duration L of scattered light from core wire A is equal to or longer than the switching time W (L+w1≧W). In order to prevent the occurrence of dead time, it is necessary to complete both step S1-B and step S2 at the timing when pulsed light is emitted to core wire B (the timing of step S3), and it is also necessary that the noise in core wire A has been sufficiently reduced. In this embodiment, since it takes time w1 for the noise to be sufficiently reduced, a dead time of time w1 occurs.

[0069] However, even in this case, the dead time can be minimized by starting step S1-B and step S2 at the same time that the incident light transmitting unit 11 emits the final pulse light to the core wire A. In other words, the switching time W and the scattered light measurement time overlap, which has the effect of reducing the dead time. Note that step S1-B only needs to be performed at a stage earlier than timing P, and the procedure may proceed in the order of step S1-B and step S2, unlike that shown in FIG. 10(A).

[0070] Figure 10(B) shows the case where the duration L of scattered light from core wire A plus time w1 is less than the switching time W (L + w1 < W). In this case, similar to the situation shown in Figure 6(B), even if measurement of scattered light from core wire A has finished and noise has sufficiently decreased (duration L and time w1 have elapsed), the switch from core wire A to core wire B has not finished (switching time W has not yet elapsed), and dead time occurs. However, compared to the prior art, the switching time W and the scattered light measurement time overlap, which has the effect of reducing dead time.

[0071] In this embodiment, too, the duration L, time w1, and switching time W that satisfy L + w1 = W may be determined using the method for determining the duration L and switching time W described in the second embodiment, while taking the time w1 into consideration.

[0072] (Fourth Embodiment) An OTDR measurement device 100 according to a fourth embodiment of the present disclosure will be described with reference to Fig. 11. The OTDR measurement device 100 according to the fourth embodiment basically has the same configuration as the OTDR measurement devices 10 according to the first to third embodiments, and includes a scattered light receiving unit 13 instead of the scattered light receiving unit 12. The scattered light receiving unit 13 will be described in detail below. The scattered light receiving unit 13 functions as a "light receiving unit."

[0073] The scattered light receiving unit 13 is an example of a light receiving unit when the OTDR measurement device employs a coherent detection configuration. The scattered light receiving unit 13 includes two polarizing beam splitters (PBS) 131A and 131B, two conversion units 132A and 132B, two balanced photo detectors (BPD) 133A and 133B, a digitizer 134, a calculation unit 135, and a display unit 136. In this embodiment, because scattered light enters from core wire A and core wire B at different times via circulators 31 and 32, two polarizing beam splitters 131, two conversion units 132, and two balanced photo detectors 133 are provided.

[0074] Specifically, because scattered light enters from core wire A and core wire B at different times, two polarization beam splitters 131A and 131B are used, couplers and phase shifters are arranged in converters 132A and 132B, and the scattered light is received by balanced photodetectors 133A and 133B. A digitizer 134 combines the electrical signals sent from the balanced photodetectors 133A and 133B and outputs the combined signal to a calculation unit 135. The calculation unit 135 performs calculations based on the data from the digitizer 134. A display unit 136 outputs the calculation results of the calculation unit 135 in a recognizable manner. For example, the timing charts in the second and third embodiments are displayed as one of the calculation results. Adjustments can be made to reduce dead time based on the displayed timing charts. The timing chart as one of the calculation results may be stored in the storage unit of the OTDR measurement device 100 and used to calculate and adjust the duration L, the time w1, and the switching time W.

[0075] When using an optical 90-degree hybrid, the scattered light receiving unit 12 is configured to use a one-input, two-output coupler to split the signal light into two paths, or to use a two-input, two-output coupler without using one input port. Therefore, when using a two-input, two-output coupler, optical loss can be avoided by effectively utilizing the unused input port. Note that scattered light from the circulator 31 may be input to one of the two inputs, and scattered light from the circulator 32 may be input to the other of the two inputs.

[0076] That is, in this embodiment, the scattered light receiving section 13 includes a two-input, two-output coupler, and scattered light from different circulators is input to each of the two inputs of the two-input, two-output coupler.

[0077] Here, "avoiding optical loss" means that even when a coherent detection configuration is adopted as in this embodiment, it is possible to suppress the occurrence of unnecessary optical loss other than the insertion loss of the optical switch. The effects of suppressing the occurrence of unnecessary optical loss will be described below.

[0078] Pulsed light is sent from the incident light transmitter 11 to the optical fiber. As light propagates through the optical fiber, Rayleigh scattering occurs due to the presence of particles smaller than the wavelength of the light and density and composition fluctuations. In this disclosure, the light propagating in the opposite direction to the light's propagation direction (backscattered light) is measured. Backscattered light is weak light. If loss occurs in the scattered light receiver 13 during measurement of this weak light, the backscattered light will be further weakened by this loss. Therefore, allowing insertion loss while preventing losses other than insertion loss has the effect of preventing the weak backscattered light from being further weakened. This allows the measurement distance in the longitudinal direction of the optical fiber to be extended for optical fibers that extend in a planar direction, enabling measurement over a wider range.

[0079] The configuration of this embodiment can be used as is for measurements in which modulation such as optical frequency multiplexing is incorporated into the probe light emitted from the incident light transmitter 11. Also, although Fig. 11 shows an example of a polarization diversity configuration, it can also be implemented in a configuration without polarization diversity so as to prevent losses other than insertion loss from occurring.

[0080] As described above, a coherent configuration such as that of the fourth embodiment allows measurements with a higher S / N ratio than a direct detection configuration, and has the effect of allowing the measurement fiber to be extended. In particular, the fourth embodiment can avoid losses other than the switch insertion loss, making it possible to take advantage of the characteristics of coherent detection.

[0081] Fifth Embodiment A fifth embodiment of the present disclosure will be described with reference to Fig. 12. In the above embodiment, the description has been given on the premise that the switch switches as shown in Fig. 3. However, the scope of the present disclosure is not limited to the adoption of a switch that switches as described above.

[0082] 12A, in this embodiment, switching between core wire A and core wire B is also performed in the same way, but as shown in Fig. 12B, the incidence of pulsed light on core wire B begins at the same time that the optical intensity of core wire A starts to drop, and therefore time w2 is not included in the switching time W. In other words, in this embodiment, pulsed light is incident on core wire B from the incident light transmitting unit 11 immediately after the connection of the right port of the switch 200, which functions as a transmitter switch, is switched from core wire A to core wire B.

[0083] Even with this configuration, it is possible to suppress the dead time, provided that all scattered light from the core wire A is acquired.

[0084] The contents of the first to fifth embodiments can be combined as appropriate.

[0085] The device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of the present disclosure is a program for causing a computer to realize each function of the device according to the present disclosure, and a program for causing a computer to execute each procedure of the method executed by the device according to the present disclosure.

[0086] The present disclosure can be applied to the information and communications industry.

[0087] 10, 10A, 100: OTDR measuring device 11: Incident light transmitting section 12, 13: Scattered light receiving section 121, 132A, 132B: Conversion section 122: Photodetector 123: Phase calculation section 131A, 131B: Polarization beam splitter 133A, 133B: Balanced photodetector 134: Digitizer 135: Calculation section 136: Display section 20: Switch for transmitting section 20A, 200: Switch 31, 32: Circulator 41, 42: Switch for receiving section

Claims

1. An optical fiber measurement system comprising: a transmitter that transmits pulsed light to a plurality of optical fibers; a transmitter that transmits scattered light from the plurality of optical fibers to a light receiving unit; and a first switching unit that is interposed between the transmitter and the transmitter and switches the connection between the transmitter and the plurality of optical fibers so that an optical transmission path for transmitting the pulsed light is formed between the transmitter and any one of the plurality of optical fibers.

2. The optical fiber measurement system according to claim 1, wherein the transmission unit comprises a plurality of circulators corresponding to the plurality of optical fibers, the first switching unit initiates switching of the connection between the transmission unit and the plurality of optical fibers before the scattered light in the optical fiber before switching passes through the circulator corresponding to the optical fiber before switching, the first switching unit comprises a plurality of connection ports corresponding to the plurality of circulators and switching the connection between the plurality of circulators and the plurality of optical fibers so that an optical transmission path for the light receiving unit to receive the scattered light is formed between any of the plurality of circulators and the light receiving unit, and the second switching unit initiates switching of the connection between the plurality of circulators and the plurality of optical fibers before the scattered light in the optical fiber before switching passes through the circulator corresponding to the optical fiber before switching.

3. The optical fiber measurement system according to claim 2, wherein the light receiving unit comprises a two-input, two-output coupler, and scattered light from different circulators is incident on each of the two inputs of the two-input, two-output coupler.

4. An optical fiber measurement method comprising: a transmitter transmitting pulsed light to a plurality of optical fibers; a transmitter transmitting scattered light from the plurality of optical fibers to a light receiving unit; and a switching unit interposed between the transmitter and the transmitter switching a connection between the transmitter and the plurality of optical fibers so that an optical transmission path for transmitting the pulsed light is formed between the transmitter and any one of the plurality of optical fibers.

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