JP2012173184A - Optical multiple reflection point specifying device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To specify a reflection point which causes multiple reflection on a branch optical fiber connected to individual subscriber-side optical line terminating devices (ONU) of a PON system.SOLUTION: An OTDR measuring device (44) is connected to a trunk optical fiber (50) instead of a station-side optical line terminating device (OLT), and an OTDR measures the position of a reflection point on an optical transmission line. A multiple reflection measuring device (10) is connected to the trunk optical fiber (50), and sequentially specifies and makes respective ONUs (56-1 to 56-n) send out an up optical signal to measure a delay time of a multiple reflection optical signal behind the up optical signal when received light includes the multiple reflection signal following the up optical signal. A reflection point specifying function (42) of a CPU (20) specifies the position of the reflection point which causes the multiple reflection from a measurement result of the OTDR measuring device (44) and a measurement result of the multiple reflection measuring device (10).

Description

  The present invention relates to an optical transmission line in a PON (Passive Optical Network) system in which a station-side optical line terminator (OLT) accommodates a plurality of subscriber-side optical line terminators (ONUs). The present invention relates to an optical multiple reflection point specifying apparatus and method for specifying a generated optical multiple reflection point.

  As means for economically providing FTTH (Fiber to the Home) service, a PON system in which an optical transmission line and its communication band are shared by a plurality of subscribers is known. In the PON system, one station side optical line terminator (OLT) accommodates a plurality of subscriber side optical line terminators (ONUs) via a passive optical transmission line.

  The PON system avoids interference between the upper and lower optical signals by using different wavelengths in the upstream and downstream directions. In a PON system in which a plurality of ONUs use the same wavelength for the upstream optical signal, a time division multiple access (TDMA) system in which upstream optical signals output from each ONU are arranged at different positions on the time axis is adopted. The light emission time and light emission timing of each ONU are controlled so that the upstream optical signals of each ONU do not collide on the optical transmission line shared by all ONUs.

  When there is some kind of fault such as poor contact of the optical fiber connector on the optical transmission line, the fault point becomes a reflection point that reflects the optical signal. In a PON system using different wavelengths on the top and bottom, the influence of the reflected light generated at such a reflection point on the receiver side is small, but when there are two reflection points on the optical transmission line, the optical signal is Multiple reflected light that has been reflected multiple times is generated. The multiple reflected light of the upstream optical signal is incident on the OLT light receiver in the same manner as the upstream optical signal.

  An optical receiver that receives an OLT upstream optical signal generally receives upstream optical signals having different light intensities from ONUs having different transmission distances, and therefore, automatic gain control (AGC: Auto Gain) that makes the received signal power level constant. Control) function is often provided. Such AGC is realized by an optical amplifier or an electric amplifier.

  Usually, the reflected light is greatly attenuated compared to the original optical signal, and the optical power level of the multiple reflected light is much smaller than the normal optical signal, but the AGC function by the optical receiver of the OLT A weak optical signal such as multiple reflected light may be amplified to a level that cannot be ignored. The multiple reflected light enters the OLT with a delay from the normal upstream optical signal, and sometimes collides with the upstream optical signal from the same or another ONU. As a result, the multiple reflected light greatly affects the communication performance of the PON system, such as frame loss and ONU link disconnection. Therefore, there is a need for a technique for easily and quickly specifying the reflection point on the optical transmission line.

  As a technique for specifying a reflection point on an optical transmission line, an OTDR (Optical Time Domain Reflectometer) method is known (Patent Documents 1 and 2). In the OTDR method, when probe pulse light is incident on an optical transmission line, backscattered light having the same wavelength as that of the probe pulse light propagates to the opposite side of the incident direction. The distance to the reflection point on the optical transmission path is measured from the time difference between the time when the probe pulse light is incident.

  In the techniques described in Patent Documents 1 and 2, fiber gratings having different wavelengths as reflection wavelengths are arranged at the user side end of the branch optical fiber, and probe light or test light of each reflection wavelength is transmitted from the OLT side. By measuring the difference in the OTDR waveform due to the incident and the backscattered light reflected by each fiber grating being reflected again by the fiber grating, it is possible to determine on which branch optical fiber the reflection point due to bending or the like exists. It can be measured.

JP 2009-63377 A JP 2010-38882 A

  The passive optical transmission line of the PON system includes a trunk optical fiber that connects an optical coupler and an OLT arranged in the middle of the passive optical transmission line, and a branch optical fiber that individually connects the optical coupler and each ONU. Thus, when a reflection point that causes multiple reflection exists on any branch optical fiber, the OTDR from the OLT side cannot identify on which branch optical fiber the reflection point exists. When two reflection points that cause multiple reflection exist on the trunk optical fiber, the position of the reflection point can be measured by OTDR from the OLT side.

  On the other hand, applying the OTDR method from the subscriber side requires dispatching workers to all subscriber homes, which is not realistic from the viewpoint of operation and maintenance costs.

  In the techniques described in Patent Documents 1 and 2, the user side end of each branch optical fiber must be equipped with a reflector having a reflection wavelength different from each other. A plurality of wavelength light sources or wavelength tunable light sources corresponding to the wavelengths must be prepared, which greatly increases the installation cost and the operation burden. Basically, the position of the reflection point is determined at a very weak scattered light level, and accurate position determination is difficult.

  It is an object of the present invention to provide an optical multiple reflection point specifying apparatus and method that can specify the positions of two reflection points that cause multiple reflection on a passive optical transmission line with a simpler configuration.

  An optical multiple reflection point specifying device according to the present invention includes a trunk optical fiber connected to an optical line terminator (OLT) and a plurality of optical network terminators (ONUs). An optical coupler that optically couples a branch optical fiber connected to each of the trunk optical fiber and the plurality of branch optical fibers, and divides the downstream light from the trunk optical fiber to divide each branch light. An upstream optical signal from any one of the optical line terminators on the subscriber side on a passive optical transmission line including an optical coupler that supplies the upstream light from each branch optical fiber to the trunk optical fiber. An optical multiple reflection point specifying device for specifying a position of a reflection point that brings about multiple reflection, wherein the station side optical line termination device of the trunk optical fiber is OTDR measuring device that measures the position of the reflection point on the passive optical transmission line from the connected side by OTDR and multiple reflections arranged on the side of the trunk optical fiber connected to the station side optical line terminator A measuring apparatus, in which each subscriber-side optical line terminator is specified in order to transmit an upstream optical signal, and when there is a multiple reflected optical signal following the upstream optical signal, the multiple reflected light with respect to the upstream optical signal A multi-reflection measuring device for measuring a signal delay time; and a reflection point specifying device for specifying a position of the reflection point from a measurement result of the OTDR measurement device and a measurement result of the multi-reflection measurement device. And

  An optical multiple reflection point specifying method according to the present invention includes a trunk optical fiber connected to a station side optical line terminator (OLT) and a plurality of subscriber side optical line terminators (ONUs). An optical coupler that optically couples a branch optical fiber connected to each of the trunk optical fiber and the plurality of branch optical fibers, and divides the downstream light from the trunk optical fiber to divide each branch light. An upstream optical signal from any one of the optical line terminators on the subscriber side on a passive optical transmission line including an optical coupler that supplies the upstream light from each branch optical fiber to the trunk optical fiber. An optical multiple reflection point specifying method for specifying a position of a reflection point that causes multiple reflection, wherein the station side optical line terminator of the trunk optical fiber includes: OTDR measurement step of measuring the position of the reflection point on the passive optical transmission line from the connected side by OTDR, and multiple reflections arranged on the side of the trunk optical fiber connected to the station side optical line terminator In the measurement step, when each of the subscriber-side optical line terminators is sequentially specified to transmit an upstream optical signal, and there is a multiple reflected optical signal following the upstream optical signal, the multiple reflected light with respect to the upstream optical signal A multiple reflection measurement step for measuring a delay time of the signal, and a reflection point specifying step for specifying the position of the reflection point from the measurement result of the OTDR measurement step and the measurement result of the multiple reflection measurement step. And

  According to the present invention, it is possible to specify the position of a reflection point that causes optical multiple reflection on a passive optical transmission line having a branched optical fiber with a simple configuration. Since the reflection point can be specified only by the device arranged on the station side such as OLT, the reflection point can be specified easily and quickly without extremely increasing the installation cost and the operation management cost.

It is a schematic block diagram of one Example of this invention. It is a main flowchart which shows the multiple reflection point specific operation | movement of a present Example. It is an example of timing of ONU light emission control, upstream reception signal, and trigger signal. It is an example of a waveform of the upstream optical signal and multiple reflected light signal after an addition average process. It is a flowchart of the multiple reflection measurement process of a present Example. It is an example of ONU information. It is a measurement example by a present Example. It is a schematic block diagram of the structure which incorporates a multiple reflection measuring apparatus in OLT.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of an optical multiple reflection point specifying system according to the present invention. FIG. 2 shows a flowchart of the main operation of this embodiment.

  In normal operation, the PON system has a main optical fiber 50 connected to the OLT, which is a station side optical line terminator, and a 1: n optical coupler 52 connected to the other end of the main optical fiber 50. It connects to ONUs 56-1 to 56-n at the user's home via the fibers 54-1 to 54-n. The optical coupler 52 equally divides the optical signal incident from the main optical fiber 50 and supplies the optical signal to the branched optical fibers 54-1 to 54-n, and the optical signals from the branched optical fibers 54-1 to 54-n are supplied to the main line. It is a passive element supplied to the optical fiber 50. The optical coupler 52 is schematically illustrated, and actually, a plurality of optical couplers may be used.

  For example, when the OLT detects that a frame loss periodically occurs in a plurality of ONUs or that a plurality of ONUs cause a link break at a time, occurrence of optical multiple reflection is suspected. When the OLT issues an alarm indicating that a failure that seems to be caused by optical multiple reflection is detected, the operator removes the OLT from the main optical fiber 50, and the main line light as shown by the broken line 46 in the OTDR measuring device 44. Optically connected to the fiber 50 (S1). Then, the reflection points on the trunk optical fiber 50 and the branched optical fibers 54-1 to 54-n are measured using the OTDR measuring device 44 (S2). In this measurement, it is impossible to specify on which branch optical fiber the reflection points on the branch optical fibers 54-1 to 54-n exist, but the absolute distance from the OLT end of the trunk optical fiber 50 can be measured.

  Next, the operator optically connects the multiple reflection measuring apparatus 10 to the trunk optical fiber 50 (S3). Although the details will be described later, the multiple reflection measuring device 10 individually transmits the upstream optical signal to each of the ONUs 56-1 to 56-n, and measures the delay time of the multiple reflected light with respect to the upstream optical signal. The distance (relative distance) between a plurality of (usually two) reflection points that yields is measured (S4).

  FIG. 3 shows an example of a waveform for explaining the delay time measurement process by the multiple reflection measurement apparatus 10. In the process of step S4, for example, as shown in FIG. 3A, the multiple reflection measuring apparatus 10 emits light control signals G (1) to G (G) that instruct the ONU 56-i to be specified in order to output an upstream optical signal. 4)... Are transmitted in the light emission period T. As shown in FIG. 3B, the designated ONU 56-i transmits the upstream optical signals R (1) to R (4) in the light emission period D according to the light emission control signals G (1) to G (4). )... Are output to the branch optical fiber 54-i at the light emission period T. When there are reflection points that cause multiple reflection on the branch optical fiber 54-i or the trunk optical fiber 50, the multiple reflection optical signals Q (1) to Q (Q) are delayed with a delay time S depending on the distance between the reflection points. 4)... Follow the upstream optical signals R (1) to R (4). Since the multiple reflection optical signals Q (1) to Q (4)... Are generally weak, the multiple reflection measurement device 10 transmits an upstream optical signal to the multiple reflection measurement device 10 as shown in FIG. A trigger signal having a period T indicating the point of incidence on R (1) to R (4)... Is generated, incident light from the trunk optical fiber 50 is sampled by this trigger signal, and the waveforms are averaged or accumulated. To do.

  The light emission period D includes the upstream optical signals G (1) to G (4)... Transmitted by the ONU and the multiple reflected optical signal Q (1) received with delay when there is an optical multiple reflection point. It is set to a sufficiently short period so as not to collide with ~ Q (4). The light emission period T is also long enough not to collide with the multiple reflected light signals Q (1) to Q (4)... And the subsequent upstream light signals G (2) to G (4). Set.

  FIG. 4 shows an example of the waveform of the addition average result of the upstream optical signal and the subsequent multiple reflected optical signal. When the peak power Z (i) of the averaged multiple reflected light signal is larger than a predetermined threshold W, it is determined that significant multiple reflection has been detected, and the delay time S of the multiple reflected light signal with respect to the upstream optical signal is measured. To do. This delay time S is a round trip delay time between two reflection points that causes multiple reflection, and can be converted into a transmission distance between the reflection points. When multiple reflection occurs on any branch optical fiber, it is possible to specify on which branch optical fiber 54-i the reflection point causing the multiple reflection is.

  Even if the measurement by the multiple reflection measurement device 10 is performed after the OTDR measurement by the OTDR measurement device 44, the positions of a plurality of reflection points that cause multiple reflection on the passive optical transmission line can be similarly specified.

  FIG. 5 shows a detailed flowchart of the multiple reflection measurement (S4) of FIG. The CPU 20 of the multiple reflection measuring apparatus 10 acquires ONU information indicating the registered ONUs 56-1 to 56-n from the OLT and stores them in the ONU information storage device 40 before starting the processing shown in FIG. The ONU information can be acquired from the OLT by reading the ONU information from the OLT to an external memory or the like and connecting the external memory to the multiple reflection measurement device 10 or by a memory that can be accessed by both the OLT and the multiple reflection measurement device 10. Alternatively, there is a method via a storage device. FIG. 6 is an example of ONU information stored in the ONU information storage device 40. The ONU information includes an ONU number indicating the order in which the ONUs 56-1 to 56-n are registered, and a MAC (Media Access Control) address that is an identifier unique to the ONUs 56-1 to 56-n.

  The CPU 20 of the multiple reflection measuring apparatus 10 sets initial parameters for generating upstream optical signals in the respective ONUs 56-1 to 56-n (S11). This initial parameter includes, for example, a light emission period T, a light emission period D (<T), a light emission control count M, and a light multiple reflection determination threshold value W. The CPU 20 acquires information about each ONU from the ONU information storage device 40 (S12).

  The CPU 20 initializes a variable i specifying the ONU to be controlled with 1 (S13). The ONU (i) specified by the variable i is, for example, the ONU 56-i. In a certain PON system, in order to control the light emission operation of ONU (i), the multiple reflection measuring device 10 needs to establish a logical link with ONU (i). Therefore, the CPU 20 refers to the timer 24 and the ONU information storage device 40, and establishes a logical link to the ONU (i) using the ONU registration process (S14). The timer 24 keeps the current time.

  Specifically, the CPU 20 causes the control frame generation device 22 to generate a Discovery_GATE message for confirming a registration request for a new ONU to the ONU (i), and receives a Register_REQ message that is a registration request signal from the ONU (i). Immediately after the time to perform, the control frame generating device 22 generates a Register message for assigning a unique logical link for ONU (i). By diverting such a registration process, the multiple reflection measurement device 10 assigns a unique logical link identifier (LLID) to the ONU (i) and establishes a logical link with the ONU (i). Establish. Even when the multiple reflection measuring apparatus 10 cannot correctly receive the upstream optical signal from the ONU (i) due to the influence of the multiple reflected optical signal, the CPU 20 can simulate the establishment of the logical link for the ONU (i) The ONU (i) emission can be remotely controlled.

  The electrical / optical (E / O) converter 26 converts the control frame (electrical signal) supplied from the control frame generation device 22 into an optical signal, that is, a downstream optical signal, and wavelength division multiplexing (WDM). Supplied to the optical coupler 28. The WDM optical coupler 28 outputs the downstream optical signal from the E / O converter 26 to the trunk optical fiber 50. This downstream optical signal enters the ONUs 56-1 to 56-n via the trunk optical fiber 50, the optical coupler 52, and the branched optical fibers 54-1 to 54-n. The ONU (i), for example, the ONU 56-i recognizes and stores the logical link assigned to itself by the Register message from the multiple reflection measuring apparatus 10.

  The CPU 20 refers to the timer 24, and causes the ONU (i) to execute upstream light transmission of the light emission period T and the light emission period D M times, so that the upstream light signal from the ONU (i) and the multiple reflected light thereby Presence / absence and delay time are measured (S15 to S18).

  Specifically, first, a variable k indicating the number of times of control is initialized with 1 (S15). The CPU 20 causes the control frame generation device 22 to generate a light emission control signal indicating the light emission period D in the ONU (i), for example, a Gate message instructing ONU (i) to permit upstream transmission (S16). This Gate message is a light emission control signal for instructing ONU (i) to output an upstream optical signal of the light emission period D after a predetermined time from receiving this message.

  The Gate message generated by the control frame generation device 22 is transmitted to the ONUs 56-1 to 56-1 through the E / O converter 26, the WDM optical coupler 28, the trunk optical fiber 50, the optical coupler 52, and the branch optical fibers 54-1 to 54 -n. 56-n. However, since a header designating ONU (i), for example, ONU 56-i as a receiving terminal, is added to this Gate message, only ONU (i) receives this Gate message, and other ONUs Discard the Gate message without receiving it.

  The ONU (i), for example, the ONU 56-i, outputs the upstream optical signal of the light emission period D to the branch optical fiber 54-i in accordance with the Gate message from the multiple reflection measuring device 10. The upstream optical signal includes data to be transmitted at this time and a Report message for reporting the amount of data to be transmitted at the next opportunity. A predetermined idle pattern is inserted in a portion that is less than the light emission period.

  When there are at least two reflection points that cause multiplexing on the branch optical fiber 54-i or the trunk optical fiber 50, the upstream optical signal output from the ONU (i) is a distance between the at least two reflection points. With multiple reflected optical signals that are delayed correspondingly. As shown in FIG. 3B, the upstream optical signal and the multi-reflection optical signal when present propagate through the branch optical fiber 54-i, the optical coupler 52, and the trunk optical fiber 50, and the multi-reflection measurement apparatus. 10 WDM optical couplers 28. The WDM optical coupler 28 supplies upstream light incident from the trunk optical fiber 50 to an optical / electrical (O / E) converter.

  The O / E converter 30 eventually converts the upstream light (the upstream optical signal from the ONU (i) and the multiple reflected optical signal when present) incident from the trunk optical fiber 50 into an electrical signal, and passes through the low-pass band. This is supplied to the filter (LPF) 32. The low-pass filter 32 is provided to prevent aliasing at the time of waveform sampling in A / D conversion at the subsequent stage. An analog / digital (A / D) converter 34 digitizes the output waveform of the filter 32 and supplies it to an averaging device 38 for S / N improvement.

  The trigger generation device 36 refers to the timer 24, generates a trigger signal (FIG. 3C) synchronized with the light emission period T of the ONU (i) whose light emission is controlled, and supplies the trigger signal to the averaging device 38. The averaging device 38 accumulates the output signal of the A / D converter 34 in synchronization with the trigger signal from the trigger generator 36 (S17). Random noise components are reduced and weak multiple reflected light signal components are detected by averaging or accumulating the upstream optical signal output from ONU (i) and the resulting multiple reflected light signal at the light emission period T. it can.

  Steps S16 and S17 are repeated M times (S18 and S19). That is, if k is not equal to M (S18), k is incremented (S19), and the process returns to step S16. When k becomes equal to M (S18), the CPU 20 reads the upstream reception signal waveform obtained by averaging from the averaging device 38, and the noise peak level Z during the TD period when the upstream optical signal from the ONU (i) is not received. (I) is calculated (S20).

  When the noise peak level Z (i) exceeds a predetermined threshold value W (S21), the CPU 20 generates multiple reflections that cannot be ignored by the upstream optical signal from the ONU (i), and the detected noise is multiple reflections. It is determined that the signal is an optical signal (S22). Then, the CPU 20 calculates the delay time S from the upstream optical signal of the determined multiple reflected light signal from the accumulated reception waveform, and converts the delay time S into the distance between the multiple reflection points (S23). The distance between the multiple reflection points is equal to the result of multiplying the speed of light on the optical fiber by half of the delay time S.

  On the other hand, if the noise peak level Z (i) does not exceed the predetermined threshold W (S21), the CPU 20 determines that multiple reflection has not occurred.

  The processes in steps S14 to S24 are executed for all the ONUs 56-1 to 56-n. Specifically, if i is not equal to n (S25), i is incremented (S26), and the process proceeds to step S14. If i is equal to n (S25), the process is terminated.

  When the branched optical fiber 54-i is broken in the first place, the ONU 56-i cannot receive the light emission control signal, and therefore the multiple reflection measuring device 10 does not receive the upstream optical signal from the ONU 56-i. As described above, when the upstream optical signal from the ONU (i) cannot be received, the multiple reflection measuring apparatus 10 assumes that the branched optical fiber 54-i is broken.

  In the delay measurement by the multiple reflection measuring device 10, although it is possible to specify on which branch optical fiber the reflection point existing on the branch optical fiber exists, the absolute position on the passive transmission path cannot be measured. However, the OTDR measurement of the OTDR measurement device 44 can measure the absolute distance of the reflection point. Therefore, the reflection point specifying function 42 of the CPU 20 compares the measurement result obtained by the OTDR measurement device 44 with the measurement result obtained by the multiple reflection measurement device 10, and determines the position of the reflection point that causes multiple reflection, which branch optical fiber 54-1. Whether it is located on 54-n is specified (S5).

  FIG. 7 shows an example in which multiple reflection points are specified from the measurement result of the OTDR measurement apparatus. FIG. 7A shows an example in which the reflection points Ra and Rb that cause multiple reflection are on the branch optical fiber 54-1, and FIG. 7B shows the case where the reflection points Ra and Rb are measured by the OTDR measuring device 44. The distance change of the reflection level of is shown. In the OTDR measurement device 44, it can be seen that the reflection points Ra and Rb are at distances La and Lb from the end of the trunk optical fiber 50. On the other hand, in the measurement by the multiple reflection measuring apparatus 10, the reflection points Ra and Rb are on the branch optical fiber 54-1, and the distance Dab between the reflection points Ra and Rb is known. By comparing the distance Dab (relative distance) between the multiple reflection points by the multiple reflection measurement device 10 with the OTDR measurement result, the positions of the reflection points Ra and Rb (which branch optical fibers are on the absolute distances La and Lb) are determined. Can be determined.

  The multiple reflection has the most adverse effect when the reflection point that causes the multiple reflection exists on the same branched optical fiber. In this embodiment, by using the OTDR measurement result in combination with this case, It is possible to specify on which branch optical fiber the reflection point is located. In addition, when one of the two reflection points that cause multiple reflection is on the trunk optical fiber 50 and the other is on any one of the branched optical fibers 54-i, this embodiment also applies to which branch optical fiber the reflection point is. In such a case, attenuation by the optical coupler 52 is added, so that the adverse effect of the multiple reflected light is small.

  Needless to say, when the position measurement value of the reflection point by the OTDR measurement device 44 is expressed in the time domain, the distance between the reflection points by the multiple reflection measurement device 10 may also be expressed in the time domain. Finally, the reflection point specifying function 42 of the CPU 20 specifies the distance of the specified reflection point from a predetermined end (usually, the end face connecting the OLT of the trunk optical fiber 50 or the optical coupler 52) and the branch optical fiber. Express with information.

  As described above, in this embodiment, it is not necessary to prepare a reflector for identifying individual branch optical fibers or a light source having a special wavelength, and the reflection points on the branch optical fibers that cause multiple reflection can be obtained. The position can be specified. Accordingly, it is possible to quickly eliminate multiple reflections that destabilize upstream optical transmission.

  The multiple reflection measuring device 10 may be incorporated in the OLT. FIG. 8 shows a schematic block diagram of an OLT having a multiple reflection measurement function. The OLT 100 shown in FIG. 8 has multiple reflections that perform the same function as the multiple reflection measurement apparatus 10 in addition to the OLT mode that operates as a normal OLT that manages communication between the ONUs 56-1 to 56-n and the upper network. Also works in measurement mode. The switch 120 is connected to the terminal A in the OLT mode, and is connected to the terminal B in the multiple reflection measurement mode.

  The operation of the OLT 100 in the OLT mode will be briefly described. The OLT 100 is connected to an upper network via a network interface (NW I / F) 110. The NW I / F 110 supplies the downlink signal from the upper network to the downlink frame transfer apparatus 112. The downlink frame transfer apparatus 112 multiplexes the downlink control frame generated by the CPU 130 on the downlink signal supplied from the NW I / F 112 on the time axis, and supplies the multiplexed signal to the electrical / optical (E / O) converter 114. The E / O converter 114 converts the downstream electrical signal transferred from the downstream frame transfer device 112 into an optical signal, and supplies the optical signal to the wavelength division multiplexing (WDM) optical coupler 116. The WDM optical coupler 116 supplies downstream optical signals for the ONUs 56-1 to 56-n to the trunk optical fiber 50, similarly to the WDM optical coupler 28.

  The WDM optical coupler 116 supplies an upstream optical signal transmitted from the ONUs 56-1 to 56-n input from the trunk optical fiber 50 to an optical / electrical (O / E) converter 118. The O / E converter 118 converts the upstream optical signal from the WDM optical coupler 116 into an electrical signal, and the output electrical signal is input to the control frame separation device 122 via the switch 120.

  The control frame separation device 122 separates the upstream electrical signal from the switch 120 into an upstream data frame directed to the upper network and a control frame such as a registration / request signal transmitted from the ONUs 56-1 to 56-n. To the upstream data frame and the latter to the CPU. The upstream frame transfer device 124 transfers the upstream data frame to the upper network via the NW I / F 110. More specifically, the uplink control frame separated by the control frame separation device 122 is a Register_REQ, Register_ACK, or REPORT message.

  When the CPU 130 receives the control frame from each of the ONUs 56-1 to 56-n, the CPU 130 calculates the upstream light transmission timing and the light emission period of each of the ONUs 56-1 to 56-n. A downlink control frame for instructing a transmission timing and a light emission period is generated. More specifically, the downlink control frame includes a Discovery_GATE, Register, or GATE message according to the stage of the registration process. The control frame generation function 132 refers to the ONU information storage device 134 and the timer 136 and generates a downlink control frame at an appropriate timing.

  When a failure caused by optical multiple reflection occurs in the PON system, the CPU 130 switches the switch 120 to the terminal B and switches to the multiple reflection measurement mode. Switching of the switch 120 may be performed automatically by the OLT 100 detecting an abnormality such as a frame loss or all ONU link disconnection, or may be performed manually by operator control.

  In the multiple reflection measurement mode, the OLT 100 operates in the same manner as the multiple reflection measurement apparatus 10 of the embodiment shown in FIG. That is, the filter 126, the A / D converter 128, the averaging device 138, and the reflection point specifying function 140 are respectively the filter 32, the A / D converter 34, the averaging device 38, and the reflection of the embodiment shown in FIG. It operates in the same manner as the point specifying function 42. The WDM optical coupler 116 transfers the probe light output from the OTDR measurement device 44 to the trunk optical fiber 50 and transfers the backscattered light and the reflected light of the probe light input from the trunk optical fiber 50 to the OTDR measurement device 44. It has a function.

  The reflection point specifying function 140 of the CPU 130 is a reflection point that causes multiple reflection from the OTDR measurement result of the OTDR measurement device 44 and the multiple reflection measurement result in the multiple reflection measurement mode, as described in the embodiment shown in FIG. Specify the position of.

  According to the present invention, it is possible to specify on which branch optical fiber an optical multiple reflection point is located for a passive optical transmission line that is partially shared by a plurality of terminals. Further, since it can be specified only by the station side device such as OLT, it can be realized inexpensively and easily without extremely increasing the installation cost and the operation management cost.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

10: Multiple reflection measuring device 20: CPU
22: Control frame generation device 24: Timer 26: Electric / optical (E / O) converter 28: Wavelength division multiplexing (WDM) optical coupler 30: Optical / electrical (O / E) converter 32: Filter 34: Analog / Digital (A / D) converter 36: Trigger generation device 38: Addition averaging device 40: ONU information storage device 42: Reflection point specifying function 44: OTDR measurement device 50: Trunk optical fiber 52: Optical couplers 54-1 to 54- n: Branch optical fiber 56-1 to 56-n: ONU
100: OLT
110: Network interface (NW / IF)
112: Downstream frame transfer device 114: Electrical / optical (E / O) converter 116: Wavelength division multiplexing (WDM) optical coupler 118: Optical / electrical (O / E) converter 120: Switch 122: Control frame separation device 124 : Upstream frame transfer device 126: Filter 128: Analog / digital (A / D) converter 130: CPU
132: Control frame generation function 134: ONU information storage device 136: Timer 138: Addition averaging device 140: Reflection point specifying function

Claims (6)

A trunk optical fiber connected to a station side optical line terminator (OLT), a branch optical fiber connected to each of a plurality of subscriber side optical line terminators (ONU: Optical Network Unit), and the trunk line light An optical coupler that optically couples a fiber and a plurality of the branched optical fibers, divides the downstream light from the trunk optical fiber, supplies the branched light to the branched optical fibers, and outputs from the branched optical fibers. Light that specifies the position of a reflection point that causes multiple reflections on an upstream optical signal from any subscriber-side optical line termination device on a passive optical transmission line composed of an optical coupler that supplies upstream light to the trunk optical fiber. A multi-reflection point specifying device,
An OTDR measuring device (44) for measuring the position of the reflection point on the passive optical transmission line by OTDR from the side of the trunk optical fiber to which the station side optical line terminator is connected;
A multiple reflection measurement device arranged on the side of the trunk optical fiber to which the station side optical line terminator is connected, sequentially specifying each subscriber side optical line terminator and sending an upstream optical signal, A multiple reflection measuring device (10) for measuring a delay time of the multiple reflected optical signal with respect to the upstream optical signal when there is a multiple reflected optical signal following the upstream optical signal;
Reflection point specifying device (42) for specifying the position of the reflection point from the measurement result of the OTDR measurement device and the measurement result of the multiple reflection measurement device
An optical multiple reflection point specifying device comprising: The multiple reflection measuring device is
Means for instructing each subscriber-side optical line terminator in turn and instructing transmission of an upstream optical signal a predetermined number of times;
A light receiving means for receiving an optical signal incident from the trunk optical fiber;
Addition averaging means for averaging the output signals of the light receiving means for the predetermined number of times;
Means for detecting the multiple reflected light from the output of the averaging means;
The optical multiple reflection point specifying device according to claim 1, further comprising means for measuring a delay time of the multiple reflected light signal with respect to the upstream optical signal. The multi-reflection measurement apparatus further includes trigger generation means for generating a trigger signal synchronized with reception of the upstream optical signal,
3. The optical multiple reflection point specifying device according to claim 2, wherein the addition averaging means averages the output signal of the light receiving means for the predetermined number of times in synchronization with the trigger signal. A trunk optical fiber connected to a station side optical line terminator (OLT), a branch optical fiber connected to each of a plurality of subscriber side optical line terminators (ONU: Optical Network Unit), and the trunk line light An optical coupler that optically couples a fiber and a plurality of the branched optical fibers, divides the downstream light from the trunk optical fiber, supplies the branched light to the branched optical fibers, and outputs from the branched optical fibers. Light that specifies the position of a reflection point that causes multiple reflections on an upstream optical signal from any subscriber-side optical line termination device on a passive optical transmission line composed of an optical coupler that supplies upstream light to the trunk optical fiber. A method for identifying multiple reflection points,
An OTDR measurement step (44) for measuring the position of the reflection point on the passive optical transmission line by OTDR from the side of the trunk optical fiber to which the station side optical line terminator is connected;
A multiple reflection measurement step arranged on the side of the trunk optical fiber to which the station side optical line terminator is connected, each of the subscriber side optical line terminators is designated in order, and an upstream optical signal is transmitted. A multiple reflection measurement step (10) for measuring a delay time of the multiple reflected optical signal with respect to the upstream optical signal when there is a multiple reflected optical signal following the upstream optical signal;
Reflection point specifying step (42) for specifying the position of the reflection point from the measurement result of the OTDR measurement step and the measurement result of the multiple reflection measurement step
An optical multiple reflection point specifying method comprising: The multiple reflection measurement step is
Designating each subscriber-side optical line terminator in turn and instructing transmission of an upstream optical signal a predetermined number of times;
A light receiving step of receiving a light signal incident from the trunk optical fiber by a light receiving means;
An averaging step for averaging the output signals of the light receiving means for the predetermined number of times,
Detecting the multiple reflected light from the addition average result of the addition averaging step;
5. The method of specifying an optical multiple reflection point according to claim 4, further comprising the step of measuring a delay time of the multiple reflected optical signal with respect to the upstream optical signal. The multiple reflection measurement step further includes a trigger generation step for generating a trigger signal synchronized with reception of the upstream optical signal,
6. The optical multiple reflection point specifying method according to claim 5, wherein the addition averaging step adds and averages the output signal of the light receiving means for the predetermined number of times in synchronization with the trigger signal.

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