JP2016109614A - Light receiving device for monitoring coated optical fiber and monitoring method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable in a short time checking of operation conditions of an optical line termination device (ONU) which is connected to a coated optical fiber attached to a downstream terminal of a splitter.SOLUTION: In a light receiving device for monitoring a coated optical fiber, a bent fiber 31 is formed on a coated optical fiber upstream from an optical splitter 151, and a probe 32 is disposed to be opposed to the bent fiber 31. An APD 331 that has a light reception diameter equal to or more than a core diameter of an optical fiber 321 in the probe 32 is disposed to be opposed to a rear end of the probe 32. The light receiving device for monitoring a coated optical fiber is configured to enhance condensing properties of leakage light such that a grin lens 322 having a diameter larger than a core diameter of the optical fiber 321 is connected to an end part, opposed to the bent fiber 31, of the optical fiber 321 in the probe 32.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for entering and exiting a light signal from the side of an optical fiber.

  In communication systems using optical fiber cables, trouble relocation work and optical fiber cable accommodation replacement work are performed. In trouble relocation work and optical fiber cable accommodation replacement work, the optical fiber cable (physical) is temporarily disconnected, and sometimes communication is interrupted while the user uses the service.

  The user will be notified in advance of the construction (communication interruption notice limited to the time zone), but the user will use the service when cutting the optical fiber so as not to reduce customer satisfaction. It is desirable to have a method that can determine whether or not it is in the middle. If the service usage status can be ascertained for each optical line, switching the optical fiber being used is postponed, and flexible switching according to the service usage status of the user minimizes the inconvenience felt by individual users. be able to.

  For this reason, as a technology for monitoring the traffic of the optical access network and determining the service usage status of the user, the optical network terminal unit (ONU (Optical Network Unit)) installed in the user's house is installed in the communication building. A method has been proposed in which a part of an upstream optical signal transmitted to a subscriber line terminating device (OLT (Optical Line Terminal)) is received and the data frame is analyzed to determine the usage state of each optical line. (Non-Patent Document 1 and Non-Patent Document 2). In this case, the upstream signal light is monitored by the side light input / output device and the APD (avalanche photodiode) in the section below the outside 8-branch splitter without entering the exchange.

Shinbo, “Study of splitter lower contrast method using upstream communication light level fluctuation detection”, IEICE Society Conference, B-10-19, 2013 Kashimura, “FTTH section communication monitoring technology that realizes confirmation during call by switching work such as relocation of trouble”, NTT Technical Journal, 2009.5, pp. 40 Shinbo, “Monitoring of upstream communication light using optical side output technology”, IEICE Technical Report, Optical Fiber Application Technology, 15-18, OPE 2013-207 (2014-02)

  By the way, in the above method, leakage light must be acquired on the lower side (ONU side) of the 8-branch splitter due to the limitation of the light receiving sensitivity when the leakage light is received by the APD. In order to determine whether or not one core can be used, the eight branched lower optical fibers must be monitored one by one.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light receiving device for monitoring an optical fiber core wire and a method for monitoring the same, which can collectively confirm the operation state of an optical line terminator (ONU) connected to the optical fiber core wire below the splitter. It is to provide.

  In order to achieve the above object, a light receiving device for monitoring an optical fiber core according to the present invention combines the upstream signal light from a plurality of first optical fiber cores to which an optical line terminator is connected, A light-receiving device for monitoring an optical fiber, which is used in a communication system including a splitter that outputs to the optical fiber of the optical fiber, and monitors the usage state of the optical line terminator, and is on the second optical fiber side of the splitter An optical fiber bending that forms a bending fiber that is attached to the optical fiber and leaks from the second optical fiber core connected to the splitter in a state in which the upstream signal light output from the optical line termination device can maintain at least communication continuation And a probe fiber that receives leakage light from the bending fiber, and one end of the probe fiber that is disposed opposite to the probe fiber and that is output from the probe fiber An avalanche photodiode having a light receiving area capable of receiving light, a monitor unit connected to the other end of the avalanche photodiode and monitoring a utilization state of the optical line termination device from leaked light received by the probe fiber, and the probe A condensing lens connected to the end of the fiber facing the bending fiber, having a diameter larger than the core diameter of the probe fiber, and condensing leakage light from the bending fiber. .

  With this configuration, a condensing lens larger than the probe fiber core diameter is connected to the end portion of the probe fiber facing the bending fiber so as to enhance the condensing performance of the leaked light. While reducing the coupling loss between the end face and the avalanche photodiode, it is possible to improve the coupling efficiency of the leaked light from the bent fiber to the probe fiber, and it is also possible to monitor the upper part of the splitter.

  Therefore, it is possible to confirm the ONU operation status of the eight optical fiber cores below the splitter only by monitoring once the leakage light from the optical fiber core above the splitter.

  In order to achieve the above object, a monitoring method according to the present invention includes a second optical fiber core that combines upstream signal light from a plurality of first optical fiber cores to which an optical line terminator is connected. A monitoring method used in a communication system including a splitter for outputting to a line and monitoring the utilization state of an optical line termination device, wherein an optical fiber bending portion is attached to a second optical fiber core side of the splitter, A first step of forming a bent fiber that leaks the upstream signal light output from the optical line termination device from the second optical fiber core wire connected to the splitter in a state where at least communication continuation can be maintained; A second step of receiving leakage light from the bending fiber with a probe fiber; and an avalanche photodiode having a light receiving area capable of receiving the leakage light, A third step of receiving leaked light output from the lobe fiber; and a fourth step of monitoring a utilization state of the optical line terminator from the leaked light obtained by the avalanche photodiode; Is provided with a condensing lens that is connected to the end facing the bending fiber, has a diameter larger than the core diameter of the probe fiber, and collects leaked light from the bending fiber.

According to the present invention, by reducing the coupling loss between the optical fiber end surface of the probe and the APD and improving the coupling efficiency of the leaked light from the bent portion of the optical fiber core wire to the optical fiber probe, the splitter Since it is possible to monitor even at the upper part, a plurality of ONUs can be confirmed together at the upper part of the splitter, and the working efficiency can be improved by 8 times. In addition, it is not necessary to determine whether the portion where the optical fiber is bent is the upper part or the lower part of the splitter for checking the ONU operation, so that the working efficiency is further improved.
Also, by increasing the light receiving diameter of the GRIN lens, manufacturing of the monitor tool (probe alignment) becomes easier, and temperature independence (the material constituting the monitor tool expands or contracts due to temperature changes). However, since the probe is displaced from the optimum position, it is strong against the displacement).

The figure which shows the structure of the system applied to embodiment of this invention. The figure which shows a mode that the optical fiber core wire of the splitter lower part using the optical side input / output technology as a prior art is specified. The figure which shows the monitoring method in the upper part of the optical splitter 151 using the light-receiving apparatus for communication monitors concerning the 1st Embodiment of this invention. The figure which shows the connection structure of the probe and monitor tool in the 1st Embodiment of this invention. The figure which shows an example of the coupling efficiency of the probe and avalanche photodiode in the 1st Embodiment of this invention. The figure which shows the change of the coupling efficiency when it shift | deviates to the perpendicular | vertical direction with respect to the bending fiber from the optimal position of a probe in the 1st Embodiment of this invention. The figure which shows the parameter for calculating | requiring the conditions which can confirm an ONU operation condition in the upper part and the lower part of the optical splitter in the 1st Embodiment of this invention.

  Prior to describing an embodiment according to the present invention, a system to which the embodiment is applied will be described. Here, examples of Non-Patent Documents 1 to 3 will be described as a representative.

  FIG. 1 is a diagram illustrating an example of a relationship between an optical line terminal (OLT) 11 and an optical network unit (ONU) 12. The OLT 11 installed in the communication building 1 is connected to a closure 15 near the subscriber home 2 via an integrated wiring module device (IDM) 14 and an optical cable 13. The closure 15 includes an eight-branch type optical splitter 151, for example. The ONU 12 in the subscriber house 2 is connected to one of the downstream terminals (hereinafter referred to as the lower part) of the optical splitter 151 via the optical fiber core wire (# 1). The ONU is also connected to the other optical fiber core wires (# 2 to # 8). By connecting the OLT 11 and the ONU 12, various services such as the Internet, optical telephone, and video distribution are provided. At this time, the upstream signal light from the ONU 12 and the upstream signal light from the other optical fiber core wires (# 2 to # 8) are combined by the optical splitter 151 and output to the OLT 11.

  By the way, since the optical cable 13 is installed outside the office, the optical cable 13 is switched every day by road widening work or telephone pole movement work. In the optical cable 13 switching work, the optical fiber in the already installed optical cable 13 is cut and connected to the newly installed optical cable side, so the service provided to the subscriber is temporarily cut off. In order to minimize the effect of switching the fiber that provides the service suddenly during the construction, the subscriber will not be able to use the service. Many operations are required. Therefore, as shown in Non-Patent Documents 1 and 2, a method for confirming the usage status of the ONU 12 using the monitor tool 16 has been proposed.

  In the above method, since the upstream signal frame from the ONU 12 can be monitored in real time and the link state and communication state of the ONU 12 can be confirmed, the operation state before and after the switching work can be confirmed.

  However, in the above method, it is necessary to branch between the OLT 11 and the ONU 12 in order to confirm an upstream signal in a state where the OLT 11 and the ONU 12 are communicating. Therefore, it is necessary to connect the monitor tool 16 to the test port 141 of the optical coupler module mounted on the integrated wiring module 14 of the communication building 1, and the use place of the monitor tool 16 is limited to one communication building. Therefore, one worker who confirms the monitor tool 16 is arranged in a place away from the construction site and one worker is arranged on the construction site, which is a total of two workers, which is not efficient. Therefore, an apparatus and a method for confirming the use status of the ONU 12 at a construction site (outside) are necessary.

  In view of the above requirements, as shown in Non-Patent Document 3, a method for confirming the use status of the ONU 12 in an off-site optical fiber core has been proposed. FIG. 2 shows an outline of Non-Patent Document 3.

  An operator forms a bent fiber 21 by bending the optical fiber core wire under the optical splitter 151 to an extent where communication between the OLT 11 and the ONU 12 is not interrupted by using the optical fiber bending device 20 outside the office. Then, communication light propagating through the fiber core of the optical fiber core wire leaks to the outside, and the leaked light can be received by the probe 22 disposed in the vicinity of the bending fiber 21. A monitor tool 23 is connected to the subsequent stage of the probe 22. By analyzing the leaked light with the monitor tool 23, the operator can confirm the usage status of the ONU 12.

  However, in the above apparatus and method, in order to determine whether or not one optical fiber can be used in the access section, the eight branched lower optical fibers must be monitored one by one.

  In contrast to the above method, it is conceivable to form the bent fiber 21 on the optical fiber core above the optical splitter 151. However, the light receiving sensitivity is limited when the leaked light is received by the APD in the monitor tool 23. Therefore, a loss of about 10 dB occurs.

  Therefore, an embodiment of the present invention in which the use state of each optical fiber core can be determined only by monitoring the optical fiber core above the optical splitter 151 once outside will be described below.

(First embodiment)
FIG. 3 shows a monitoring method in the upper part of the optical splitter 151 using the optical fiber core line monitoring light receiving device according to the first embodiment. In FIG. 3, the same parts as those in FIG.
An operator forms the bent fiber 31 by bending the optical fiber core wire above the optical splitter 151 using an optical fiber bending device 30 so that communication between the OLT 11 and the ONU 12 is not interrupted. Then, communication light propagating through the fiber core of the optical fiber core wire leaks to the outside, and the leaked light can be received by the probe 32 disposed in the vicinity of the bending fiber 31.

  The optical fiber bending device 30 bends the optical fiber core wire on the upper side of the optical splitter 151, for example, with a bending radius of 3 mm or more and a center angle of 30 degrees or less in order to realize a gentle bending with no communication interruption.

  A monitor tool 33 is connected to the subsequent stage of the probe 32. By analyzing the leakage light with the monitor tool 33, the operator can confirm the usage status of the ONU 12.

FIG. 4 shows a connection configuration between the probe 32 and the monitor tool 33.
The probe 32 includes an optical fiber 321 as a probe fiber formed by a core 321a and a clad 321b, and a gradient index lens (hereinafter referred to as a GRIN lens) connected to the tip of the optical fiber 321 on the bending fiber 31 side. 322).

  The GRIN lens 322 collects the leaked light from the bending fiber 31 of the optical fiber core wire to the core 321a of the optical fiber 321 connected in the subsequent stage. Here, as the optical fiber 321 used for the probe 32, a graded index (GI) fiber capable of reducing the coupling loss with the APD 331 connected in the subsequent stage is used.

  A monitor tool 33 incorporating an APD 331 is disposed at the subsequent stage of the probe 32. Thereby, the leaked light from the bending fiber 31 is supplied to the APD 331 via the probe 32.

  The APD 331 receives leaked light obtained by combining the upstream optical signals of the eight optical fiber cores below the optical splitter 151 by the optical splitter 151, and converts the leaked light from an optical signal to an electrical signal. The monitor tool 33 measures the optical signal intensity for each wavelength of the leaked light converted into an electrical signal by the APD 331, and outputs the measurement result to a display unit (not shown). Thereby, the operator can specify the optical fiber core wire in use among the eight optical fiber core wires under the optical splitter 151.

  Here, when the ONU 12 is in use, the intensity of the upstream signal light (wavelength 1310 nm) coming from the optical fiber core wire (# 1) is compared with a threshold value (for example, the light receiving sensitivity of the APD 331) by the monitor tool 33. Since it is equal to or greater than the threshold value, it is output to the display unit. On the other hand, the upstream signal light (for example, wavelength 1312 nm) arriving from the unused optical fiber (# 2) is compared with the threshold value by the monitor tool 33 and is output to the display unit because it is less than the threshold value. Not.

Next, measurement results of the probe 32 according to the first embodiment will be described.
For example, the optical fiber 321 of the probe 32 does not deteriorate the coupling efficiency with the APD 331 in the monitor tool 33, and is a commercial product that is generally used and has a graded index (GI) with a core diameter of 62.5 μm. ) Fiber is used. The GRIN lens 322 mounted at the tip of the optical fiber 321 is a GRIN lens having a light receiving diameter of 120 μm, 170 μm, and 230 μm.

  FIG. 5 shows the mode field dependence of the coupling efficiency when the GRIN lens 322 is provided at the tip of the optical fiber (GI fiber) 321 and when the GRIN lens 322 is not provided. The measurement wavelength is 1310 nm, and the optical fiber 321 used for the measurement has a small mode field diameter (8.43 μm), a large one (9.39 μm), and a currently used optical fiber 321. In addition, an intermediate one (8.8 μm) is used. In FIG. 5, the diamond points are measured values of coupling efficiency when an optical fiber (GI fiber) 321 not connected to the GRIN lens 322 is used, and the square points are optical fibers connected to a GRIN lens 322 having a light receiving diameter of 120 μm ( (GI fiber) 321 is a measurement value of coupling efficiency when using 321, and a triangular point is a measurement value of coupling efficiency when using an optical fiber (GI fiber) 321 connected with a GRIN lens 322 having a light receiving diameter of 170 μm, The measurement value of the coupling efficiency when using an optical fiber (GI fiber) 321 to which a GRIN lens 322 having a light receiving diameter of 230 μm is connected is shown.

In addition, the solid line in FIG. 5 indicates conditions for realizing a light receiving device for monitoring an optical fiber core wire in which the ONU operation status can be confirmed at the upper and lower portions of the outside optical splitter 151. P _ONU is the output power of the _ONU 12, L is a line loss including the optical splitter 151 having eight branches, η ₁ is the coupling efficiency of the probe 32, η ₂ is the coupling efficiency between the APD 331 and the optical fiber (GI fiber) 321, and R _mon is Assuming that the light receiving sensitivity of the APD 331 in the monitor tool 33 is a value as shown in FIG. 7, the coupling efficiency η ₁ needs to be −24.5 dB or more from the following equation (1).

  From FIG. 5, it can be confirmed that as the mode field diameter increases, the power of the leaked light from the bending fiber 31 increases, so that the coupling efficiency increases. The coupling efficiency when using an optical fiber (GI fiber) 321 to which the GRIN lens 322 is not connected is less than −24.5 dB in the case of an optical fiber having a mode field diameter of 8.43 μm. The conditions for realizing the optical fiber monitor light-receiving device are not satisfied.

  On the other hand, when the GRIN lens 322 is connected to the tip of the optical fiber (GI fiber) 321, it can be seen that it is −24.5 dB or more in all mode field diameters. Since the mode field diameter of the optical fiber 321 actually laid cannot be discriminated from the appearance, all of the mode field diameters of 8.43 to 9.39 μm are required in order to realize the optical fiber core monitor light receiving device. In this range, the coupling efficiency needs to be −24.5 dB or more.

FIG. 6 shows a change in coupling efficiency when the probe 32 is shifted from the optimum position (position where the coupling efficiency is maximized) in a direction perpendicular to the bending fiber 31 (a direction perpendicular to the paper in FIG. 4). FIG.
By using the GRIN lens 322, the probe 32 can reduce the deterioration of the coupling efficiency with the APD 331 due to the deviation from the optimum position. Further, when the light receiving diameter of the GRIN lens 322 is increased, although the coupling efficiency of the probe 32 with the APD 331 is not improved so much, the degradation of the coupling efficiency due to the deviation from the optimum position is further reduced.

  As a result, the manufacture of the monitor tool 33 (alignment of the probe 32) is facilitated, and temperature independence (the material constituting the monitor tool 33 expands or contracts due to a temperature change, so that the probe 32 is moved from the optimum position. It can be expected to have an effect such as being stronger against the deviation.

  Therefore, according to the first embodiment, the optical fiber (GI fiber) 321 in which the GRIN lens 322 having a light receiving diameter of 120 μm, 170 μm, and 230 μm is connected to the tip is used as the probe 32, so that the access network is actually used. The leakage light from the upper optical fiber core of the optical splitter 151 located outside is confirmed, and the ONU operation status of the eight optical fiber cores under the optical splitter 151 is confirmed by one monitor. be able to.

(Second Embodiment)
In the second embodiment, an example in which a single mode fiber is used as the optical fiber 321 of the probe 32 will be described.

  The core diameter of the commercially available single mode fiber for the probe 32 is 8.5 μm, which is smaller than the light receiving diameter of the APD 331 in the monitor tool 33 is 55 μm.

  Therefore, the coupling loss between the probe 32 and the APD 331 can be reduced as compared with the case where the GI fiber is used.

(Operational effects of the first and second embodiments)
According to the first and second embodiments, the GRIN lens 322 that is larger than the core diameter of the optical fiber 321 is connected to the end of the probe 32 that faces the bending fiber 31 of the optical fiber 321 to collect light leaked. Since the coupling loss between the end face of the optical fiber 321 of the probe 32 and the APD 331 is reduced, the coupling efficiency of the leaked light from the bending fiber 31 to the probe 32 can be improved. Monitoring can also be performed on the top of the optical splitter 151.

  Therefore, the ONU operation status of the eight optical fiber cores below the optical splitter 151 can be confirmed by only monitoring the leakage light from the optical fiber core above the optical splitter 151 once.

(Other embodiments)
In the first embodiment, the bending radius of the bending fiber is 3 mm or more and the bending center angle is 30 degrees or less. However, if the communication can be continued, the bending radius is set to a different numerical value from the bending center angle. Also good.

  In each of the above-described embodiments, examples of using a GRIN lens having a light receiving diameter of 120 μm, 170 μm, and 230 μm have been described. However, the present invention is not limited to this example, and any GRIN lens that is larger than the core diameter of an optical fiber to be used. The GRIN lens may be used in the range where the light receiving diameter is 120 μm or more and 230 μm or less. Further, a condensing lens other than the GRIN lens may be used.

  Furthermore, in the first embodiment, the example in which the APD is built in the monitor tool has been described. However, the APD may be connected to the outside of the monitor tool.

  In short, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Communication building, 2 ... Subscriber house, 11 ... OLT, 12 ... ONU, 13 ... Optical cable, 14 ... Integrated wiring module apparatus, 15 ... Closure, 30 ... Optical fiber bending machine, 31 ... Bending fiber, 32 ... Probe, 33: Monitor tool, 141: Test port, 151: Optical splitter, 321: Optical fiber, 321a: Core, 321b: Cladding, 322: GRIN lens, 331: APD

Claims (8)

An optical line terminator used in a communication system including a splitter that combines upstream signal light from a plurality of first optical fiber cores to which an optical line terminator is connected and outputs the multiplexed signal light to a second optical fiber core. An optical fiber monitoring device for monitoring the usage state of the optical fiber,
A second optical fiber core attached to the splitter on the second optical fiber core side and connected to the splitter in a state where at least communication of the upstream signal light output from the optical line termination device can be maintained. An optical fiber bending section for forming a bending fiber to leak from,
A probe fiber for receiving leakage light from the bending fiber;
An avalanche photodiode having one end disposed opposite to the probe fiber and having a light receiving area capable of receiving leakage light output from the probe fiber;
A monitor unit connected to the other end of the avalanche photodiode and monitoring a utilization state of the optical line termination device from leaked light received by the probe fiber;
A condensing lens that is connected to an end of the probe fiber facing the bending fiber, has a diameter larger than a core diameter of the probe fiber, and collects leaked light from the bending fiber. A light receiving device for monitoring an optical fiber core.   2. The optical fiber monitor light receiving device according to claim 1, wherein the probe fiber is a graded index fiber having a core diameter equal to a light receiving diameter of the avalanche photodiode.   The light receiving device for monitoring an optical fiber core wire according to claim 1, wherein the probe fiber is a single mode fiber having a core diameter smaller than a light receiving diameter of the avalanche photodiode.   2. The light receiving device for monitoring an optical fiber according to claim 1, wherein the condensing lens is a refractive index distribution lens having a light receiving diameter of 120 μm or more and 230 μm or less. An optical line terminator used in a communication system including a splitter that combines upstream signal light from a plurality of first optical fiber cores to which an optical line terminator is connected and outputs the multiplexed signal light to a second optical fiber core. Monitoring method for monitoring the usage status of
An optical fiber bending section is mounted on the second optical fiber core side of the splitter, and the upstream signal light output from the optical line termination device is connected to the splitter in a state where communication can be continued at least. A first step of forming a bent fiber that leaks from the optical fiber core of the second optical fiber;
A second step of receiving leaked light from the bending fiber with a probe fiber;
A third step of receiving leaked light output from the probe fiber by an avalanche photodiode having a light receiving area capable of receiving the leaked light;
A fourth step of monitoring the usage state of the optical line termination device from the leaked light obtained by the avalanche photodiode,
The probe fiber includes a condensing lens that is connected to an end facing the bending fiber, has a diameter larger than a core diameter of the probe fiber, and collects leakage light from the bending fiber. Monitoring method.   The monitoring method according to claim 5, wherein the probe fiber is a graded index fiber having a core diameter equal to a light receiving diameter of the avalanche photodiode.   The monitoring method according to claim 5, wherein the probe fiber is a single mode fiber having a core diameter smaller than a light receiving diameter of the avalanche photodiode.   The monitoring method according to claim 5, wherein the condenser lens is a refractive index distribution lens having a light receiving diameter of 120 μm or more and 230 μm or less.

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