JP4383162B2 - Optical branch line monitoring system - Google Patents

Description

  The present invention relates to an optical branch line monitoring system in an optical multi-branch communication system in which a plurality of slave station devices are connected to a master station device, and in particular without affecting the reception function of each slave station device. The present invention relates to an optical branch line monitoring system capable of monitoring an optical communication line by a simple method.

Currently, in order to introduce FTTH (Fiber To The Home) at a low price, an optical PDS (Passive Double Star) system that shares one OLT (Optical Line Terminal) grounded in the office among many users has been proposed. Yes. FIG. 4 is a diagram showing a schematic configuration of this optical PDS system. In FIG. 4, an optical splitter 28 is provided in the middle of the basic optical line 22 connected to the transmission apparatus 10, the basic optical line 22 is optically branched by the optical splitter 28, and this optically branched basic optical line 22 is further split. Are split into a plurality of branched optical lines 1a _{1 to} 1a ₈ via an optical splitter 3 outside the office and connected to each ONU (Optical Network Unit) 20 in the user (subscriber) 24.

This optical PDS system uses an OTDR (Optical Time Domain Reflectometer) 2 to monitor an abnormality of an optical fiber or an optical communication device as an optical line medium, and a fiber selector (FS) 2 and an optical coupler 18 from the OTDR 2. The monitoring light is output to the trunk optical line 20 via the optical line 20 and the monitoring light returned from each ONU 20 is detected. That is, the monitoring light output from the optical coupler 18 propagates along the backbone optical line 20 together with the communication light propagated by the transmission apparatus 10 and reaches each ONU 20 via the optical splitter 3 and the branched optical lines 1a _{1 to} 1a _8. returns to the monitoring light only is reflected OTDR 2, to monitor the abnormality of the branch optical 1a ₁ to 1A ₈ by measuring the back monitoring light.

As the monitoring method, for example, the length of the branch optical 1a ₁ to 1A ₈ set to different lengths for each branch optical 1a ₁ to 1A _8, the optical path length between each ONU202 and OTDR2 is The measurement data such as the delay time of the return light of the monitoring light in the normal state is obtained for each of the branched optical lines 1a _{1 to} 1a ₈ in advance, and the measurement data of the return light of the monitoring light at the time of monitoring is obtained. By performing the comparison, the branched optical lines 1a _{1 to} 1a ₈ having an abnormality are specified (see Non-Patent Document 1). In this case, the monitoring light uses a single wavelength.

Further, a different monitoring light wavelength is assigned to each of the branched light lines 1a _{1 to} 1a ₈ so that the OTDR 2 can output a variable wavelength, and the OTDR 2 monitors the increase or decrease in the amount of reflected light of the monitoring light, so Abnormalities _{1 to} 1a ₈ are detected, and each of the branched optical lines 1a _{1 to} 1a ₈ having an abnormality is specified by the wavelength of the monitoring light (see Non-Patent Document 2).

Further, instead of branching the monitoring light of different wavelengths to the respective branch optical lines 1a _{1 to} 1a ₈ , there is one that demultiplexes the monitor light only to the corresponding branch optical lines 1a _{1 to} 1a ₈ by wavelength routing ( Non-Patent Document 3). In order to perform monitoring of this wavelength routing method, it is necessary to provide an optical line monitoring device 103 shown in FIG.

The optical line monitoring device 103, the optical filter 130 first, and the wavelength λa of the communication light inputted demultiplexes the monitor light having a wavelength λc ₁ ~λc _n, the circuit 110 of the arrayed waveguide grating The communication light from the communication light input unit 131 is input, and the monitoring light is input from the monitoring light input unit 132. The communication light is transmitted through the filter 137 that transmits the communication light and reflects the monitoring light, enters the slab waveguide 133 through the communication light input waveguide 142, spreads in the slab waveguide 133, and is transmitted to each light output guide. The light enters the waveguide 136 and exits from its output end.

  On the other hand, the monitoring light enters the slab waveguide 133 through the monitoring light input waveguide 143, spreads by the diffraction effect of the slab waveguide 133, enters the arrayed waveguide 134, and is reflected by the filter 37. The light propagates back and forth in the waveguide 134, passes through the slab waveguide 133 again, is demultiplexed for each wavelength, and is emitted from a different light output waveguide 136 for each wavelength.

"1.6 μm band fault isolation test technology for branched optical lines" Yamamoto et al., 1994 IEICE Autumn Meeting B-846 "Study on fault monitoring method in PDS line" Ito et al., 1996 IEICE General Conference B-1073 "Individual loss distribution measurement of branched optical lines by test wavelength allocation method" Tanaka et al., 1996 IEEJ Electronics, Information and Systems Conference A-9-4

  However, in the optical branch line monitoring system described in Non-Patent Document 1, it is necessary to design each branch optical line to have a different length at the time of laying, and this design work takes time and labor. was there.

  In the optical branch line monitoring system described in Non-Patent Document 2, since the monitoring light is branched and inputted to all ONUs, even if the wavelength of the monitoring light corresponding to the own terminal can be reflected, Since the corresponding monitoring light cannot be reflected, it is necessary to provide an additional filter element such as a WDM filter so that the monitoring light is not received by the communication device on the terminal side, which hinders downsizing and makes the configuration complicated. There was a problem of becoming.

  Furthermore, in the optical branch line monitoring system described in Non-Patent Document 3, since the monitoring light is routed, no additional filter element is required, but the optical splitter has a wavelength separation function for performing this routing. There is a problem that miniaturization of the optical splitter is hindered. In particular, the outdoor closure tray that houses the optical splitter becomes difficult to store, and it is necessary to replace the closure tray and the circuit having the wavelength separation function together, which takes time and labor for the replacement. There was a problem.

  The present invention has been made in view of the above, and it is possible to easily and accurately detect and identify a failure in a branched optical line without making a significant change in the optical multi-branch communication system. The purpose is to provide a system.

  In order to solve the above-described problems and achieve the object, the present invention monitors each branch line of an optical multi-branch communication system in which a master station device and a plurality of slave station devices are connected by an optical splitter. In the optical branch line monitoring system, each slave station device includes a reflection filter that reflects light having a unique monitoring wavelength allocated to each slave station device, and the master station device monitors each monitor at the input end of the reflection filter. Output control means for emitting each monitor wavelength light is provided so that the intensity of the wavelength light is less than the minimum reception intensity of each slave station device.

  In addition, according to the present invention, in the above invention, the master station device detects the monitoring wavelength light reflected from the reflection filter using a photon counting method.

  In the present invention according to the present invention, the reflection filter is a fiber Bragg grating.

  In the present invention, the monitoring wavelength and the reflection wavelength of each reflection filter are in the range of 1625 nm to 1675 nm.

  According to this invention, the output control means of the master station apparatus emits each monitor wavelength light so that the intensity of each monitor wavelength light at the input end of the reflection filter is less than the minimum reception intensity of each slave station apparatus. Therefore, there is an effect that the branch optical line can be monitored with a simple configuration without affecting the communication on the slave station side.

  Embodiments of an optical branch line monitoring system according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an optical branch line monitoring system according to an embodiment of the present invention. In this optical branch line monitoring system, a trunk optical line 22 is connected to the transmission apparatus 10, and the trunk optical line 22 is optically branched by an optical splitter 28 and branched into a plurality of trunk optical lines 22. The branched main optical line 22 extends outside the station via the optical coupler 18 and is branched into multiple branched optical lines 1a _{1 to} 1a ₈ by the outdoor optical splitter 3. Each of the branched optical lines 1a _{1 to} 1a ₈ subjected to optical multi-branching is connected to each ONU 20 in the user 24.

  The control unit 26 performs output control of the monitoring light of the variable wavelength output from the OTDR 2 and outputs it to the FS and also controls reception measurement. The OTDR 2 is connected to the optical coupler 18 via the control unit 26 and the FS 25.

  Each ONU 20 is assigned a monitoring light wavelength unique to each ONU 20, and FBGs (Fiber Bragg Grating) 20-1 to 20-8 are provided in each ONU 20 to reflect the monitoring light having a specific wavelength.

The control unit 26 periodically emits monitoring light having wavelengths λc ₁ to λc ₈ to be monitored, and outputs the monitoring light to the trunk optical line 22 via the optical coupler 18. At this time, the FS 25 selects the trunk optical line 22 to be output. In the optical coupler 18, the communication light of wavelength λb propagating from the transmission device 10, for example, is input to the optical splitter 3 with monitoring light of wavelength [lambda] c _1, are light multi-branching in each branch optical 1a ₁ to 1A _8, each ONU20 Reach. That is, as shown in FIG. 2, the monitoring light having the wavelength λc ₁ is reflected only by the FBG 20-1, and the communication light having the wavelength λb is received by all the ONUs 20. However, FBG20-3, without reflection wavelength [lambda] c _1, is received by the optical receiver 31-3 are optical / electrical conversion by O / E section, it is input to the reception processing section 33-3 side. When a signal corresponding to this wavelength λc ₁ is received, a communication error or the like occurs, affecting communication.

  Therefore, in this embodiment, the monitoring light intensity emitted from the OTDR 2 is adjusted so that the received light intensity of the monitoring light is less than the minimum receiving sensitivity in the light receiving units 31-1 to 31-8. FIG. 3 is a diagram illustrating specific attenuation of the monitoring light intensity. As shown in FIG. 3, the connection loss from the OTDR 2 to the coupler 18 is 2 dB, the branch loss in the optical coupler 18 is 8 dB, the transmission loss from the optical coupler 18 to the splitter 3 is 5 dB, and the branch loss in the optical splitter 3 is 10 dB. Then, the loss between OTDR2 and ONU20 is 25 dB. Here, if the minimum receiving sensitivity of the ONU 20 is −30 dBm, it is only necessary to output monitoring light of less than −5 dBm from OTDR2. In this embodiment, -10 dBm monitoring light is output from the OTDR 2, and at the final ONU 20 end, −35 dBm is input. Accordingly, since the reception input of −35 dBm is less than the minimum reception sensitivity of −30 dBm, it is not received by the optical reception unit of the monitoring light and does not affect communication. Note that the monitoring light is transmitted in pulses. The communication light having the wavelength λa is transmitted from the ONU 20 to the transmission apparatus 10 side.

  Here, since the monitoring light intensity that is the reflected return light from each of the FBGs 20-1 to 20-8 becomes small, the OTDR 2 preferably detects the monitoring light using a photon counting method. Thereby, highly sensitive light measurement can be performed, and a detailed light measurement waveform can be obtained.

  Since the FBGs 20-1 to 20-8 can be accommodated in the optical connectors 30-1 to 30-8 and formed in the optical fiber, the ONU 20 can be reduced in size and cost can be reduced. Can be planned.

  Furthermore, by setting the wavelength of the monitoring light to 1625 nm to 1675 nm, the monitoring light wavelength conforming to the international standard can be obtained, the standardization of the system components can be facilitated, and the cost can be easily reduced.

It is a figure which shows schematic structure of the optical branch line monitoring system which is embodiment of this invention. It is a figure which shows the transmission state of the monitoring light and communication light in the ONU side. It is a figure which shows the loss change of monitoring light. It is a figure which shows schematic structure of the conventional optical branch line monitoring system. It is a figure which shows the structure of the optical splitter which has the wavelength separation function of monitoring light.

Explanation of symbols

1a _{1 to} 1a ₈ branch optical line 2 OTDR
3,28 Optical splitter 10 Transmission device 18 Optical coupler 20 ONU
20-1 to 20-8 FBG
22 Basic optical line 24 User 25 Fiber selector (FS)
26 Control unit 30-1, 30-3 Optical connector 31-1, 31-3 Optical receiving unit 32-1, 32-3 O / E unit 33-1, 33-3 Reception processing unit λa, λb Wavelength of communication light λc _{1 to} λc ₈ monitoring light wavelength

Claims (3)

In an optical branch line monitoring system for monitoring each branch line of an optical multi-branch communication system in which a master station device and a plurality of slave station devices are optically multi-branched connected by an optical splitter,
Each slave station device includes a reflection filter that reflects light having a unique monitoring wavelength assigned to each slave station device.
The master station device emits each monitor wavelength light with a preset output so that the intensity of each monitor wavelength light at the input end of the reflection filter is less than the minimum reception intensity of each slave station device, and the reflection filter An optical branch line monitoring system for detecting a monitoring wavelength light reflected from a light using a photon counting method . The optical branch line monitoring system according to claim 1 , wherein the reflection filter is a fiber Bragg grating. The optical branch line monitoring system according to claim 1 or 2 , wherein the monitoring wavelength and the reflection wavelength of each reflection filter are in the range of 1625 nm to 1675 nm.

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