Control system

Abstract

A control system 1 comprises: a measurement instrument 21 for measuring, at a terminal end of a transmission path 2 through which light of a plurality of wavelengths propagates, the power of light partially reflected toward a starting end; and a control instrument 22 for lowering the power of the light if the measured power is lower than a threshold value.

Description

Control System

[0001] The present disclosure relates to control systems.

[0002] When high-power laser light is input and transmitted through an optical fiber, an increase in optical loss may occur due to a sudden change in the shape of the transmission path. An example of an unexpected change in shape is an unexpected cut or bend. If high-power light continues to be input into the optical fiber despite a sudden increase in optical loss, there is a risk of exposure to the laser light if there is a person near the loss location. Furthermore, there is a high possibility that the transmission path will suffer fatal damage at the loss location due to coating burnout or fiber fuse.

[0003] In high-power laser devices, the influence of returning light on the light source is significant. One method is to irradiate the processing surface with monitor light and monitor the monitor light to control the laser light (see Patent Document 1).

[0004] There is also a technology that reduces or stops the output of the light source when a change in shape occurs in the transmission path (Non-Patent Document 1).Non-Patent Document 1 feeds back the change through the exchange of signals between two optical fibers.

[0005] Japanese Patent Application Laid-Open No. 2018-129452

[0006] Recommendation ITU-T G. 664.

[0007] When high optical power is input into a single optical fiber, a technology is required that detects the increase in loss due to deformation of the transmission line and controls the optical power.

[0008] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a technology that can detect an increase in loss due to deformation of the transmission path and control the optical power when high optical power is input into a single optical fiber.

[0009] A control system according to one aspect of the present disclosure includes a measuring instrument that measures the power of light at the end of a transmission path through which light of multiple wavelengths propagates, a portion of which is reflected back toward the starting end, and a controller that reduces the power of the light if the measured power is lower than a threshold value.

[0010] According to the present disclosure, it is possible to provide a technology that can detect an increase in loss due to deformation of a transmission line when high optical power is input into a single optical fiber, and control the optical power.

[0011] FIG. 1 is a diagram illustrating the system configuration of a control system according to a first embodiment. FIG. 2 is a flowchart illustrating processing in the control system. FIG. 3 is an example of a spectrum when a light source with a wide line width is used. FIG. 4 is a diagram illustrating the system configuration of a control system according to a second embodiment. FIG. 5(a) is a diagram illustrating an example of the transmittance of an FBG and the spectrum of transmitted light, and FIG. 5(b) is a diagram illustrating an example of the spectrum of reflected light from the FBG. FIG. 6 is a diagram illustrating the system configuration of a control system according to a third embodiment. FIG. 7 is a diagram illustrating the hardware configuration of a computer used in the controller.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0013] (Control System) A control system 1 according to the present disclosure detects an increase in loss due to deformation of a transmission line and controls the optical power when high optical power is input in an optical fiber communication network formed by a transmission line 2 using an optical fiber cable having one or more cores, as shown in Fig. 1. In the example shown in Fig. 1, the transmission line 2 is described as having one core, but this is not limiting, and the shape of the transmission line 2 is not important in the present disclosure.

[0014] The control system 1 includes a measuring instrument 21 and a controller 22 .

[0015] The measuring instrument 21 measures the power of light that is partly reflected toward the starting end of the transmission path 2 at the end of the transmission path 2 through which light of a plurality of wavelengths propagates.

[0016] If the power measured by the measuring instrument 21 is lower than the threshold, the controller 22 reduces the power of the light of the wavelength of the light source 11. For example, when the transmission line 2 is introduced, the controller 22 measures the power of light that is partly reflected at the end of the transmission line 2 toward the start end, and sets a threshold in advance for determining loss in the transmission line 2. The controller 22 compares the power measured by the measuring instrument 21 with the preset threshold to evaluate the loss in the transmission line 2, and, if necessary, reduces the power of light input to the core wire to be measured so as to prevent disadvantages associated with the occurrence of optical loss in the transmission line 2.

[0017] This allows the control system 1 to immediately control the optical power after detecting an increase in loss due to deformation of the transmission line. The control system 1 makes it possible to prevent people present at the location where loss occurs in the transmission line 2 from being exposed to laser light and to prevent damage to the transmission line 2 due to coating burnout or fiber fuse at the location where loss occurs.

[0018] First Embodiment A control system 1 according to a first embodiment will be described with reference to FIG.

[0019] The control system 1 includes a first light source 11, a second light source 23, an optical isolator 13, a wavelength multiplexer 14, an FBG (Fiber Bragg Grating) 15, a photodetector 16, an optical circulator 18, a measuring instrument 21, and a controller 22. In the control system 1, the direction of the first light source is referred to as the starting side, and the side of the photodetector 16 is referred to as the terminal side.

[0020] The first light source 11 inputs light of a first wavelength λ1 to one core wire of the transmission line 2. The first light source 11 inputs light to be mainly used to the transmission line 2. The light to be mainly used is light used for the purpose for which the transmission line 2 is provided. The purpose for which the transmission line 2 is provided is, for example, data communication or optical power supply.

[0021] The second light source 12 inputs light of a second wavelength λ2 into the core line into which light of a first wavelength λ1 is input. Light of multiple wavelengths, the first wavelength λ1 and the second wavelength λ2, are input into one core line of the transmission line by the first light source 11 and the second light source 12. The second light source 12 inputs monitor light into the transmission line 2. The monitor light is input into the transmission line 2 for the purpose of monitoring the transmission line 2.

[0022] The optical isolator 13 is an element that transmits light emitted by the first light source 11 only in the direction of the arrow, specifically, only toward the terminal end. The optical isolator 13 does not allow light propagating from the terminal end to the starting end to pass through to the first light source 11.

[0023] The wavelength multiplexer 14 multiplexes the light of the first wavelength λ1 input from the first light source and the light of the second wavelength λ2 input from the second light source 12, and inputs the multiplexed light to the terminal end. The wavelength multiplexer 14 is, for example, a WDM (Wavelength Division Multiplexing) coupler. The wavelength multiplexer 14 inputs the light from the terminal end to the measuring instrument 21. The wavelength multiplexer 14 also inputs the light from the terminal end to the optical isolator 13, but the optical isolator 13 does not allow the light from the terminal end to pass to the first light source 11.

[0024] The FBG 15 is an example of a reflector. The FBG 15 reflects only the second wavelength λ2 of the light input from the starting end toward the starting end.

[0025] The optical receiver 16 receives light input from the starting end side. In the present disclosure, the optical receiver 16 receives only the first wavelength λ1 of the first wavelength λ1 and the second wavelength λ2 input from the starting end side.

[0026] The optical circulator 18 inputs the light of wavelength λ 2 input from the second light source 12 to the wavelength multiplexer 14 , and also inputs the light input from the wavelength multiplexer 14 to a measuring instrument 21 .

[0027] The measuring instrument 21 measures the power of the light of the second wavelength λ2 reflected toward the starting end at the end of the transmission line 2. In the present disclosure, the measuring instrument 21 measures the power of the light of the second wavelength λ2 reflected by the FBG 15.

[0028] If the optical power of the second wavelength λ2 is lower than the threshold, the controller 22 reduces the optical power of the first wavelength λ1. The controller 22 sets the threshold based on the optical power of the second wavelength λ2 measured when the transmission line 2 is installed, for example. The controller 22 compares the optical power of the second wavelength λ2 measured by the measuring instrument 21 with a preset threshold, and determines whether to maintain or reduce the optical power of the first wavelength λ1 emitted by the first light source 11. If the optical power of the first wavelength λ1 is to be reduced, the controller 22 inputs an instruction to the first light source 11 to reduce the power.

[0029] In a control system 1 configured to propagate high-power light using optical fibers, monitor light having a longer wavelength than the wavelength of light primarily used is input, and the monitor light is reflected at the system terminal to detect abnormalities in the transmission path from changes in the loss of the monitor light. The wavelength of the light source primarily used is a first wavelength λ1, for example, 1550 nm. In the first embodiment, the light primarily used is, for example, power supply light used as optical power. The wavelength of the monitor light is a second wavelength λ2, for example, 1625 nm.

[0030] 1, the FBG 15 reflects only the 1625 nm monitor light just before the optical receiver 16 after passing through the transmission path 2. The reflected light returns to the port to which the monitor light is connected by the wavelength multiplexer 14, and is propagated by the optical circulator 18 or the like to the port of the measuring instrument 21, rather than to the second light source 12 for the monitor light, and is received there.

[0031] The measuring instrument 21 measures the optical power of the monitor light. If the power drops compared to the optical power when the transmission line 2 is in a normal state, the controller 22 controls the power of the light emitted by the first light source 11. For example, if the power drops by 1 dB, the controller 22 controls the power of the first light source 11 by reducing the output power of the feed light input by the first light source 11 to 10 mW or less or by stopping the input of light by the first light source 11.

[0032] Referring to FIG. 2, the process according to the present disclosure will be described.

[0033] In step S1, for example, immediately after constructing the transmission line 2, the wavelengths of a first wavelength λ1 and a second wavelength λ2 are input to one core wire, and the control system 1 is used to obtain the power of the second wavelength λ2 reflected by the FGB 15 as a reference value (P0).

[0034] After constructing the transmission path 2, the control system 1 measures the power of the second wavelength λ2 periodically or at random timing. For example, in step S2, the process waits for the timing of measurement to arrive, and when the timing arrives, the process proceeds to step S3. In step S3, the measuring instrument 21 measures the optical power (P1) of the monitor light of the second wavelength λ2.

[0035] In step S4, the controller 22 calculates Loss, which is the power difference between the optical power P0 measured in step S1 and the optical power P1 measured in step S3. If the Loss is greater than a threshold in step S5, the controller 22 reduces the output of the first light source 11 in step S8. The threshold to be compared with Loss is determined in consideration of safety and depending on the power of the optical fiber power feed system to be constructed. The threshold may be about 1 dB, or may be as high as 0.5 dB, and is set as appropriate.

[0036] According to the control system 1, it is possible to sequentially detect abnormalities in the transmission line 2 and control the output of the light source in response to the occurrence of an abnormality.

[0037] In the control system 1 according to the first embodiment, two wavelengths of light, a first wavelength λ1 and a second wavelength λ2, are input to one optical fiber. However, the present invention is not limited to this. For example, the wavelength of the power supply light used for optical fiber power supply may be 1550 nm, the wavelength of the light used for data communication may be 1310 nm, and the monitor light may be set to 1625 nm, which is longer than these wavelengths.

[0038] The monitor light may be either shorter or longer than the wavelength band that is mainly used, but is preferably on the longer wavelength side in that it is easier to evaluate bending loss.

[0039] Although the FBG 15 has been given as an example of a reflector for the monitor light, the reflector is not limited to the FBG 15 as long as it is capable of reflecting only the monitor light. The reflector only needs to have a resolution that can distinguish the wavelength of the monitor light.

[0040] Even after detecting an abnormality and stopping the light source, the control system 1 can identify the abnormal location in the transmission line 2. The control system 1 can easily detect the abnormal location in the transmission line 2 by inputting light from a port for inputting monitor light and performing a line test using an OTDR (Optical Time Domain Reflectometer) or the like.

[0041] Second Example In the second example, a case will be described in which the measuring instrument 21 uses a part of the wavelength of the wavelength band that is mainly used as the monitor light. In the second example, a case will be described in which the output of the light source is controlled by monitoring a part of the power supply light in the optical fiber power supply system.

[0042] In optical fiber power supply, a light source with a relatively wide linewidth is used to avoid input power limitations due to nonlinearity in the optical fiber. For example, when a light source with a center wavelength of 1550 nm and a linewidth of 2 nm is used, the spectrum broadens to 1546 nm on the short wavelength side and 1554 nm on the long wavelength side, as shown in Figure 3.

[0043] In the second embodiment, a portion of this broadened spectrum is reflected, and the measuring instrument 21 monitors the reflected power, thereby detecting an abnormality in the transmission line 2. FIG. 3 shows an example of a calculated spectrum when the linewidth is 2 nm and the input power is 1 W. As shown in FIG. 3, when the laser spectrum has a Gaussian shape, approximately 80% of the input power is concentrated within the 2 nm linewidth range. On the short wavelength side and long wavelength side outside the 2 nm linewidth, approximately 20% of the input power exists. In the second embodiment, a portion of the power outside the 2 nm linewidth is used to detect an abnormality in the transmission line 2.

[0044] In the second embodiment, the wavelength λ1 of the power supply light is set to 1550 nm, and the wavelength λ2 of the monitor light is set to 1553 nm.

[0045] A control system 1a according to the second embodiment will be described with reference to Fig. 4. The control system 1a according to the second embodiment differs from the control system 1 according to the first embodiment in that it includes a second light receiver 17 instead of the second light source 12 and the optical circulator 18, and in that the function of the FBG 15 is different.

[0046] In the second embodiment, the FBG 15 reflects only the light of wavelength λ2 of the monitor light among the light input from the transmission line 2. The FBG 15 uses a wavelength that does not significantly reduce the power of the power supply light as its Bragg wavelength. The half-width of the FBG 15 can generally be manufactured to about 0.05 nm to 1 nm, and the reflectivity can be controlled to about 5 to 95%. Since it is sufficient to measure a power that can detect an abnormality in the transmission line 2, it is advisable to appropriately set the reflectivity of the FBG 15 in accordance with the power of the power supply light and the detection sensitivity of the measuring instrument 21, etc.

[0047] The second optical receiver 17 receives the monitor light reflected by the FBG 15 and inputs it to the measuring instrument 21. The measuring instrument 21 measures the optical power of the monitor light with wavelength λ2.

[0048] In the second embodiment, the light source 11 inputs light in a wavelength band including a second wavelength λ2 as light of a plurality of wavelengths to the transmission line 2 .

[0049] The measuring instrument 21 measures the power of a portion of the light of the second wavelength λ2 reflected toward the starting end at the end of the transmission line 2. If the power of the light of the second wavelength λ2 is lower than a threshold, the controller 22 reduces the power of the light of the wavelength input by the light source 11.

[0050] 5 shows an example of calculations of the spectrum of light reflected by the FBG 15 and the spectrum of the transmitted feed light, assuming that the power of the feed light is 1 W, the center wavelength of the FBG 15 is 1553 nm, the half-width is 0.5 nm, and the reflectivity is 80%. The dotted line in Fig. 5(a) shows the transmittance of the FBG 15, and the solid line shows the spectrum of the transmitted feed light. As shown in Fig. 5(a), there is no apparent significant change in the spectrum after passing through the FBG 15.

[0051] Figure 5(b) shows the spectrum of light reflected by the FBG 15. As shown in Figure 5(b), the reflected light has a central wavelength of 1553 nm. The transmitted power in this case is 995 mW, and the reflected power is approximately 5 mW. The central wavelength and transmittance of the FBG 15 can be set arbitrarily, so they may be set appropriately depending on the system.

[0052] In the second embodiment, the 1553 nm light reflected by the FBG 15 propagates through the transmission line 2 and is received by the second photodetector 17 on the wavelength λ2 side through the wavelength multiplexer 14 .

[0053] After constructing the transmission path 2, the power of this wavelength λ2 is measured. The control system 1a monitors the change in optical power as shown in the flow of Fig. 2, and controls the output of the light source 11 if the change exceeds a threshold. The control system 1a can immediately reduce the output of the light source 11 if an abnormality occurs in the transmission path.

[0054] In the second embodiment, similarly to the first embodiment, an abnormality can be easily detected by carrying out a line test using an OTDR or the like from the port of wavelength λ2.

[0055] Third Example In a third example, a case will be described in which the measuring instrument 21 uses, as monitor light, backward Raman scattered light generated by light in the wavelength band that is mainly used.

[0056] In an optical fiber, fiber nonlinearity occurs depending on the optical power input. In fiber nonlinear Raman scattering, Stokes light and anti-Stokes light are generated, which are frequency-shifted to the longer and shorter wavelength sides of the input light. In the second embodiment, the power of either or both of the Stokes light and anti-Stokes light, which are wavelength-shifted from the input light, is used as monitor light to detect abnormalities in the transmission line 2.

[0057] 6 shows a control system 1b according to a third embodiment. The control system 1b according to the third embodiment differs from the control system 1a shown in the second embodiment in that it does not include an FBG 15. In the second embodiment, the light mainly used is the power supply light, which has a first wavelength λ1. The monitor light has a wavelength λ2 of light generated by backward Raman scattering of the power supply light.

[0058] Light including light of a first wavelength λ1 is input to the transmission path 2 as light of multiple wavelengths. A measuring instrument 21 measures the power of Raman scattered light of the light of the first wavelength λ1. If the power of the Raman scattered light is lower than a threshold, a controller 22 reduces the power of the light of the wavelength input by the light source 11.

[0059] The feed light has a wavelength λ1 and is input to the transmission line 2 through the wavelength multiplexer 14. The feed light travels forward, specifically toward the terminal end. In the transmission line 2, light shifted to a longer or shorter wavelength side than the wavelength λ1 due to Raman scattering propagates backward, specifically toward the starting end.

[0060] For example, when the wavelength λ1 is 1550 nm, light of approximately 1663 nm, which is shifted in frequency by 13.2 THz, is generated as the Stokes light. Since this 1663 nm light propagates toward the light source 11, the wavelength multiplexer 14 separates the light of wavelength λ2 and sends it to the second photodetector 17, allowing the measuring instrument 21 to monitor the power of the Stokes light.

[0061] In the third embodiment, the Stokes light used for anomaly detection propagates forward, specifically toward the photodetector 16, and this may result in a decrease in the power of the monitor light detected by the measuring instrument 21. Therefore, in the third embodiment, a reflector that reflects the wavelength of this Stokes light may be installed at the end of the transmission line 2, as shown in Fig. 4. This allows the measuring instrument 21 to obtain sufficient power of the monitor light.

[0062] Similar to the first and second embodiments, the control system 1b according to the third embodiment measures the power of the wavelength λ2 after constructing the transmission path 2. The control system 1b monitors the change in optical power as shown in the flow chart of FIG. 2 and controls the output of the light source 11 when the change exceeds a threshold. The control system 1b can immediately reduce the output of the light source 11 when an abnormality occurs in the transmission path.

[0063] In the third embodiment, similarly to the first and second embodiments, an abnormality can be easily detected by carrying out a line test using an OTDR or the like from the port of wavelength λ2.

[0064] The control system 1 according to the present disclosure uses, as monitor light, light that has a different wavelength from the light that is primarily used in the transmission path 2 and that propagates in the opposite direction to the light that is primarily used. The control system 1 measures the power of the monitor light to detect an abnormality caused by loss in the transmission path 2. Furthermore, upon detecting an abnormality, the control system 1 controls the output of the light that is primarily used.

[0065] The control system 1 according to the present disclosure can detect an increase in loss due to deformation of a transmission line and control the optical power when high optical power is input into a single optical fiber. This ensures the safety of the transmission line 2 and prevents light from scattering at an abnormality location and affecting the surrounding environment, thereby improving the reliability of systems that use optical fiber transmission lines.

[0066] The controller 22 of the present embodiment described above is, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906. In this computer system, the CPU 901 executes a program loaded on the memory 902, thereby realizing each function of the controller 22.

[0067] The controller 22 may be implemented by one computer or by multiple computers, or may be a virtual machine implemented on a computer.

[0068] The program of the controller 22 can be stored in a computer-readable recording medium such as a HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), DVD (Digital Versatile Disc), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0069] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present disclosure.

[0070] REFERENCE SIGNS LIST 1 control system 2 transmission path 11, 12 light source 13 optical isolator 14 wavelength multiplexer 15 FBG 16, 17 photoreceiver 18 optical circulator 21 measuring instrument 22 controller 901 CPU 902 memory 903 storage 904 communication device 905 input device 906 output device

Claims

1. A control system comprising: a measuring instrument that measures the power of light at the end of a transmission path through which light of multiple wavelengths propagates, a portion of which is reflected back toward the start end; and a controller that reduces the power of the light if the measured power is lower than a threshold value.

2. The control system of claim 1, wherein the light of the plurality of wavelengths comprises light of a first wavelength λ1 and light of a second wavelength λ2, the measuring instrument measures the power of the light of the second wavelength λ2 reflected toward the starting end at the end of the transmission line, and the controller reduces the power of the light of the first wavelength λ1 when the power of the light of the second wavelength λ2 is lower than a threshold value.

3. The control system according to claim 1, wherein the light of the multiple wavelengths is light in a wavelength band including a second wavelength λ2, the measuring instrument measures the power of a portion of the light of the second wavelength λ2 that is reflected back to the starting end at the end of the transmission line, and the controller reduces the power of the light of the multiple wavelengths when the power of the light of the second wavelength λ2 is lower than a threshold value.

4. The control system according to claim 1, wherein the light of the plurality of wavelengths includes light of a first wavelength λ1, the measuring instrument measures the power of Raman scattered light of the light of the first wavelength λ1, and the controller reduces the power of the light of the plurality of wavelengths when the power of the Raman scattered light is lower than a threshold value.

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