JP4910102B2 - Optical fiber termination status judgment method - Google Patents

Description

  The present invention relates to a method for determining a termination state of a user's home side of an optical fiber core wire in a PON (Passive Optical Network) type optical access network.

  The fiber to the home (FTTH) service that connects the network operator's office (station) and the user's home with optical fiber is spreading. In FTTH, a so-called PON type network configuration in which an optical splitter is provided outside a station building and an optical fiber is branched is generally used. In the PON configuration, the optical fiber can be used more effectively than the non-PON (single star or the like).

  All the branched optical fibers are not necessarily terminated at the user's home, and some optical fiber cores may stand by without being used. Hereinafter, an optical fiber core that is already used by a specific user is referred to as “active”, and an optical fiber core that is not used by any user is referred to as “non-active”.

  By the way, there is a case where it is desired to cut the non-working optical fiber core wire on the user's home side from the branch point due to the necessity of construction work or the like. At this time, it is necessary for an operator to check the termination state of the optical fiber outside the office so that the working optical fiber core wire is not cut accidentally.

  In a network configuration referred to as a single star network that does not have a branch between a station building and a user's home, a method is known that can effectively and reliably confirm the termination state of an optical fiber. However, when the network form is PON, there is no known method that can reliably determine that the optical fiber core to be cut is non-working.

  In Patent Document 1, an optical filter type reflector is installed immediately before the optical receiver at each user's house in the PON form, the distance to the reflection position is calculated by an optical pulse test, and the optical fiber core is intentionally Disclosed is a method for determining whether an optical fiber is intended or not by comparing the measured value when bending loss is given to the measured value without bending loss. . However, this technique relates to a so-called cord control method for determining whether or not the selected optical fiber core is intended by the operator, and it is not possible to determine the current / non-current using this method.

In Patent Document 2, in a single star network, a plurality of continuous lights having different wavelengths are incident from a network operator office, and the presence or absence of the test light blocking filter is confirmed by observing the magnitude of the reflectance at each wavelength. An apparatus is disclosed. However, this technique can only confirm the mounting status of the filter, and cannot determine whether the optical fiber is currently used or not. Moreover, there is a risk of erroneous determination depending on the wavelength used.
Japanese Patent No. 3324612 JP 2003-294777 A

As described above, in the existing technology, it is difficult to reliably determine the state of the end of the optical fiber from the outside of the network operator office in the PON form, and there is an awaiting provision of some technology.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber termination state determination method capable of reliably determining the termination state of an optical fiber in the PON mode.

  In order to achieve the above object, according to one aspect of the present invention, in a PON (Passive Optical Network) type optical network formed by branching a backbone fiber into a plurality of optical fiber cores, connection of band reflection type filters is performed. In which the termination state of the optical fiber core wire is determined in association with the presence or absence of the test light, the test light having the first wavelength within the reflection band of the band reflection filter and the second wavelength outside the reflection band. A first measurement step of individually injecting the test light from the backbone fiber and measuring the reflectance distribution of each test light, and after this first measurement step, disturb any one of the optical fiber core wires. A disturbance step; after the disturbance step, a second measurement step in which the test light having one of the first and second wavelengths is incident from the backbone fiber and the reflectance distribution thereof is measured; and the first measurement A specific step of specifying an optical fiber core that gives different results in the step and the second measurement step, and a ratio of reflectances of the respective wavelengths in the first measurement step for the optical fiber core specified in the specific step And a determination step of determining whether or not the band reflection filter is connected. An optical fiber termination state determination method is provided.

  By taking such a measure, the reflectance is measured by a technique such as OTDR based on different wavelengths. Then, based on the reflectance ratio of each wavelength, the termination state of the optical fiber that is the target of the operation (construction or the like) is determined. In particular, since the termination state is determined based on the reflectance ratio of each wavelength instead of the absolute value of the reflectance, accurate determination can be realized in the PON mode.

  According to the present invention, it is possible to provide an optical fiber termination state determination method capable of reliably determining the termination state of an optical fiber in the PON mode.

  FIG. 1 is a diagram showing an optical network that can use the termination state determination method according to the present invention. This network forms a so-called PON type optical access network. In FIG. 1, a backbone fiber 100 extended from a network operator office 10 (hereinafter referred to as office 10) to an optical access network is branched into a plurality of optical fiber cores 8 by an optical splitter 2 provided outside the office 10. The

  Among these, the optical fiber drawn into the user's home is connected to the user home transmission device and terminated at this device. That is, the optical fiber core wire 8-1 drawn into the user home 11-1 is connected to the user home transmission device 7-1, and the optical fiber core wire 8-2 drawn into the user home 11-2 is connected to the user home transmission device 7-1. 7-2. These optical fiber core wires 8-1 and 8-2 are currently used.

  In this embodiment, the test light blocking filter is inserted immediately before the current optical fiber is connected to the user home transmission device. That is, the optical fiber core wire 8-1 is connected to the user home transmission device 7-1 via the test light blocking filter 6-1 and the optical fiber core wire 8-2 is connected to the user home via the test light blocking filter 6-2. Connected to the transmission device 7-2. Each of the filters 6-1 and 6-2 has a characteristic of blocking only the test light and transmitting the communication light. As a result, the test light incident on the backbone fiber 100 from the office 10 can be prevented from reaching the user home transmission apparatuses 7-1 and 7-2, and the occurrence of communication errors can be prevented.

  On the other hand, the optical fiber (optical fiber core 8-r) that is not connected to the user's home is only cut off or terminated with a dummy optical connector or the like, and its end point is processed as an open point 5. Of course, no test light blocking filter is attached. The optical fiber core wire 8-r in this state is not used.

  In this embodiment, a two-wavelength OTDR (Optical Time Domain Reflectometer) 1 is provided in the office 10 in order to determine the termination state of the optical fiber core wire 8. This two-wavelength OTDR1 has a function equivalent to a very general optical pulse tester that can measure the reflectance distribution of an optical fiber as a function of distance. However, in this embodiment, the wavelength of the test light pulse incident on the backbone fiber 100 is set to two characteristic values. This will be described in detail with reference to FIG.

  In this embodiment, whether the optical fiber core wire 8 is used or not is distinguished by identifying whether the test light blocking filter 6 is attached to the end of the optical fiber core wire 8 or the open point 5. The terminal state is determined by the observation using the two-wavelength OTDR 1 by the joint work of the observer of the office 10 and the worker dispatched to the new construction point 3. The observer and the worker have communication means such as a radio telephone (not shown) for mutual communication. In addition, in FIG. 1, the operator gives a bend 4 to the fiber core wire during the test. Further, a loss 9 generated in the optical fiber core wire is shown with reference numeral 9.

  FIG. 2 is a diagram showing the blocking (reflection) characteristics of the test light blocking filters 6-1 and 6-2 in FIG. That is, the test light blocking filters 6-1 and 6-2 reflect light in the wavelength range of λL to λH and transmit light outside this range. In FIG. 2, λ1 and λ2 are the wavelengths of the test light with the two wavelengths OTDR1 incident on the backbone fiber 100, and the first wavelength λ1 is set within the reflection band. That is, λL <λ1 <λH, and the second wavelength λ2 is set to λ2 <λL or λH <λ2.

FIG. 3 is a flowchart showing an embodiment of a method for determining the state of the end of the optical fiber 8 according to the present invention. This procedure is executed by cooperation between the observer and the worker using communication means. Hereinafter, the details of the procedure will be described using the example of the test pulse waveform of FIG.
In FIG. 3, the observer operates the two-wavelength OTDR1 in the office 10 and switches the test wavelength to λ1 and λ2 to perform an optical pulse test (step S1). At this time, the test waveform observed by the observer is as shown in FIG. In the example of FIG. 1, there are three optical fiber cores 8-1, 8-2, and 8 -r on the user side of the optical splitter 2, so that there are three reflectance peaks reflecting the reflection from the end point. Stand at each wavelength. The distance to the reflection point is known from each peak, and the reflectance varies depending on the wavelength. These values are measured assuming that the reflectance at the wavelength λ1 is R1, and the reflectance at the wavelength λ2 is R2.

In step S1, the power of the test light incident on the backbone fiber 100 must be at a level that does not affect the user home transmission device 7. Specifically, since λ1 is in the blocking region of the test light blocking filter 6, the blocking amount of the test light blocking filter 6 is X (dB), the loss of the optical fibers 100 and 8 is L (dB), and user home transmission. If the allowable input to the device 7 is Y (dBm), the allowable test optical power is
[Y + X + L (dBm)]
It is as follows. Also, since λ2 is in the transmission band of the test light blocking filter 6, the allowable test light power is
[Y + L (dBm)]
It is as follows.

  Next, the operator selects the optical fiber core wire (8-r) that he / she intends to cut, and gives a bending loss to the core wire 8-r as a disturbance (step S2). If this bending loss is set so as to give a loss only to the test light and not a loss to the communication light, the test can be performed in-service.

The loss caused in the light by bending increases as the wavelength increases. For example, when the test light wavelength is 1.65 μm and the communication light wavelength is 1.55 μm, in a normal single mode optical fiber, the bend radius is about 1 to 2 cm, and the loss in the test light is several dB per bend. It is known that loss in communication light can be reduced to 1 dB or less.
Next, the operator notifies the observer that the bend has been given by the communication means (step S3). In response to this, the observer conducts the optical pulse test again with the optical fiber bent (step S4). This second test may be performed at either wavelength λ1 or λ2. For example, examples of results of measurement at wavelength λ1 are shown in FIGS.

  In an optical fiber having a bending loss, reflection from the far end is lost or attenuated. As shown in FIGS. 4B to 4D, one of the reflection peaks disappears and becomes two. Using this result, in this embodiment, the active / non-active status of the optical fiber is determined based on the following logic.

That is, the reflectivity R observed in step S1 is determined in each optical fiber core wire unless the loss of the optical fiber in the middle section is taken into consideration.
<Reflectance R1 of wavelength λ1>
[Termination case with test light blocking filter 6: 0 dB (almost 100%)]
[Termination case with open point 5: about -14 dB (by Fresnel reflection)]
<Reflectance R2 of wavelength λ2>
[Termination case with test light blocking filter 6: about -14 dB (by Fresnel reflection)]
[Termination case with open point 5: about -14 dB (by Fresnel reflection)]
It is clear that This is because, as shown in FIG. 2, the wavelength λ1 is in the reflection band of the test light blocking filter 6 and returns to the light source, whereas the wavelength λ2 is in the transmission band.

Therefore, the ratio R1 / R2 of the reflectance between the two wavelengths is
[Termination case by test light blocking filter 6: R1 / R2 = 14 dB]
[Termination case by open point: R1 / R2 = 0 dB]
It becomes. Both are ratios calculated in decibels.

  The reflectances R1 and R2 are apparently reduced due to the influence of the loss 9 in the optical fiber in the middle section. Therefore, there is a risk of causing an error if the fiber termination form is determined from a simple size comparison of R1 alone or R2 alone. However, in this embodiment, attention is paid to the fact that the reflectance ratio R1 / R2 between the two wavelengths is substantially unchanged even if there is a loss in the middle section. This is because a loss coefficient that is an index of loss is expressed as a function of wavelength. Based on this fact, it is possible to determine that the end form of the optical fiber core wire is the test light blocking filter 6 or the open point 5.

When step S4 is completed, the observer compares the result of step S1 with the result of step S4, and extracts an event that causes a change in the reflectance ratio (step S5). Then, the reflectance at two wavelengths is analyzed for the reflected event in which the change has occurred, and is determined as follows.
[If R1 / R2≈14 dB , it is concluded that the optical fiber core is terminated by the test light blocking filter, and is therefore in use]
[If R1 / R2≈0 dB, it is concluded that the optical fiber core is terminated by an open point 5 and is therefore not active]
According to the above procedure, it becomes possible to determine whether the end of the optical fiber core wire selected by the operator and giving the bending loss in step S2, that is, whether the end of the optical fiber is active or not.

  The above discussion is based on the premise that the loss of the optical fiber in the middle section is constant regardless of the wavelength (λ1 or λ2). As shown by reference numeral 9 in FIG. 1, if a bending loss occurs in the middle section of the optical fiber core, the loss of the optical fiber due to bending increases as the wavelength increases, so the above assumption may be lost.

Assuming that the loss amounts of the bending loss 9 in FIG. 1 are L1 and L2 for wavelengths λ1 and λ2, respectively, L1> L2 when λ1> λ2. In such a case, the reflectance ratio between the wavelengths observed at the termination by the test light blocking filter 6 is
R1 / R2 = L2-L1 (dB)
It becomes. Depending on the value of L2−L1, this is the reflectance ratio of the termination due to the open point 5;
R1 / R2 = -14 dB
It turns out that it may become near or equal, and the determination of both may become impossible.

There are two ways to avoid this situation.
First, it may be set as λ1 <λ2. In other words, the second test wavelength set in the transmission region of the test light cutoff filter 6 is set on the longer wavelength side than the cutoff region. Since L1 <L2 in this way, the ratio of the reflectance between the wavelengths observed at the termination by the test light blocking filter 6,
R1 / R2 = L2-L1 (dB)
Is always greater than 0 dB. Therefore, the reflectance ratio at the end due to the open point 5,
R1 / R2 = -14 dB
And can be clearly distinguished.

Second, even if λ1> λ2, λ1 is set as close to λ2 as possible. By doing so, the above situation can be avoided.
If λ1 and λ2 are sufficiently close to each other, the wavelength dependence of loss can be almost ignored. Specifically, if the wavelength difference is about 10 nm, the loss wavelength dependency hardly occurs. Therefore, it is preferable to set λ2 set in the transmission region of the test light blocking filter 6 as close as possible to λ1 in the transmission region.

  That is, λ2 set in the transmission band of the test light blocking filter 6 is set as close as possible to the boundary with the blocking area within the transmission band. Specifically, since the cutoff band of the test light cutoff filter 6 is normally around 1650 ± 5 nm, the above discussion is valid if λ1 = 1650 nm and λ2 = 1640 nm.

  FIG. 5 is a diagram for explaining a method for determining whether an optical fiber is used / not used in a single star network for comparison. This method is applied in a network form called a single star network that does not have a branch between the office 10 and the user's home. In FIG. 5, it is assumed that a construction involving cutting of a non-working optical fiber that has been laid outside the office 10 has occurred. In such a case, the worker goes to the new construction point 3 and cuts the optical fiber core after confirming that the optical fiber core to be cut is inactive.

  In the single star network, whether the optical fiber is connected to the intra-office transmission device 13 or not can be identified in the office 10 as to whether the optical fiber is currently used or not. Accordingly, the test light is incident on the non-working core from the office 10, and the worker dispatched to the new construction point detects the leak test light 12 leaking from the optical fiber and emitting it at the site. It can be confirmed that the optical fiber core to be cut is not used. However, this method cannot be used in a passive double star PON assumed in this embodiment.

The following technologies are also known in the single star network. That is, a plurality of continuous lights having different wavelengths are incident on the optical fiber from the office, and the presence or absence of the test light blocking filter is confirmed by observing the magnitude of the reflectance at each wavelength. In this technique, by measuring the magnitude of the reflectance from the cutoff filter at the two test light wavelengths λ′1 and λ′2 respectively set in the cutoff region and the transmission region of the cutoff filter,
[Reflection intensity at test wavelength λ′1> Reflection intensity at test wavelength λ′2: With cutoff filter]
[Reflectance at test wavelength λ′1≈Reflectance at test wavelength λ′2: no cutoff filter]
Make a decision. However, this method can only confirm the mounting condition of the filter, and it is not possible for an outdoor worker to determine whether the optical fiber is currently used or not based on this conclusion.

Furthermore, there is a risk of erroneous determination depending on the wavelength setting of λ′1 and λ′2. For example, if λ′1 = 1.65 μm and λ′2 = 1.55 μm, the bending loss in the middle section of the optical fiber is larger as the wavelength is longer, so if the test light blocking filter is attached,
[Reflection intensity at test wavelength λ′1> Reflection intensity at test wavelength λ′2]
It looks like, apparently
[Reflection intensity at test wavelength λ′1≈Reflection intensity at test wavelength λ′2]
It is because it may become. When bending with a radius of 1 to 2 cm is actually applied, the difference in bending loss at wavelengths of 1.55 μm and 1.65 μm may reach several dB per number of turns. It is enough to make a mistake.

  On the other hand, in this embodiment, the termination state of the optical fiber core wire is determined by detecting the presence or absence of connection of the test light blocking filter 6 that blocks the test light. That is, when the two-wavelength OTDR1 is connected to the upstream side (office 10 side) of the optical splitter 2 and the reflection (cutoff) band of the test light blocking filter 6 is the wavelength λL to λH, the wavelength λ1 of the test light pulse of the two-wavelength OTDR1 , Λ2, λ1 is within the cutoff band, and λ2 is outside the cutoff band. Under this setting, the first measurement of the reflectances R1 and R2 with the two wavelengths λ1 and λ2 is performed on the plurality of optical fiber cores 8 without intentionally bending. Next, only the optical fiber core wire to be operated is intentionally bent, and the reflectance is measured for the second time at a wavelength of either λ1 or λ2. For an optical fiber whose reflectance has changed before and after the measurement, based on the first measurement value, if R1 / R2 = 14 dB, it is determined that it is terminated by the test light blocking filter 6, and if R1 / R2 = 0 dB, it is opened. It is determined that the end point is a point 5. In this way, by performing OTDR measurement using different wavelengths, erroneous determination due to unintended loss in the middle section can be prevented, and termination determination in the PON mode can be performed.

  Therefore, according to this embodiment, it becomes possible to detect the form of the end of the optical fiber core 8 in the network configuration having a branch by an optical splitter or the like outside the office 10, and this makes it possible to It is possible to make a non-working determination. That is, it becomes possible to detect the presence or absence of an optical filter at the end of the selected optical fiber core. Therefore, it is possible to provide an optical fiber termination state determination method that can reliably determine the termination state of the optical fiber in the PON mode.

  In the above embodiment, in step S2, the operator gives a bending loss to the planned cutting core wire to enable identification by the observer. Instead of measuring this loss, the polarization state of the light wave propagating in the optical fiber is disturbed, and the reflected waveform of the disturbed core wire is observed by the polarization OTDR capable of detecting the polarization state. May be identified. The easiest way to change the polarization state of propagating light is to bend the optical fiber by a remote operator. Even with such a method, only the identification method in step S2 changes, and the determination conditions after step S1 and step S3 are exactly the same. In addition, various embodiments can be implemented without changing the gist of the present invention.

The figure which shows the optical network of the PON form which can utilize the termination state determination method based on this invention. The figure which shows the interruption | blocking (reflection) characteristic of the test light cutoff filters 6-1 and 6-2 of FIG. 5 is a flowchart showing an embodiment of a method for determining the state of termination of the optical fiber 8; The figure which shows the example of the result of the measurement implemented by the procedure of FIG. The figure for demonstrating the method to determine active / inactive of an optical fiber in a single star network for a comparison.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 2 wavelength OTDR, 2 ... Optical splitter, 3 ... New construction point, 4 ... Bending, 5 ... Opening point, 6 (6-1, 6-2) ... Test light cutoff filter, 7 (7-1, 7- 2) User home transmission device, 8 (8-1, 8-2, 8-r) ... Optical fiber core wire, 9 ... Loss, 10 ... Network operator office, 11 (11-1, 11-2) ... User Home, 100 ... backbone fiber

Claims (4)

In a PON (Passive Optical Network) type optical network formed by branching a backbone fiber into a plurality of optical fiber cores, the termination state of the optical fiber cores is determined in association with the presence or absence of connection of a band reflection filter. A way to
The test light having the first wavelength within the reflection band of the band reflection filter and the test light having the second wavelength outside the reflection band are individually incident from the backbone fiber, and the reflectance distribution of each test light is obtained. A first measuring step for measuring
After this first measurement step, a disturbance step for giving disturbance to any one of the optical fibers,
After this disturbance step, a second measurement step in which the test light having one of the first and second wavelengths is incident from the backbone fiber and its reflectance distribution is measured;
A specifying step of specifying an optical fiber core that gives different results in the first measurement step and the second measurement step;
For the optical fiber core specified in this specifying step, the ratio of the reflectance of each wavelength in the first measurement step is the value when the termination is due to the band reflection filter, or the termination due to the open end is And a determination step of determining whether or not the band reflection type filter is connected.   The optical fiber termination state determination method according to claim 1, wherein the second wavelength is located on a longer wavelength side than the reflection band.   2. The optical fiber termination state determination method according to claim 1, wherein the second wavelength is set closer to the first wavelength and closer to the first wavelength than the reflection band. When the reflectance of the first wavelength in the first measurement step is R1, and the reflectance of the second wavelength in the first measurement step is R2,
If the ratio of R1 to R2 is approximately 0 dB, the determination step determines that there is no connection of the band reflection filter, and if the ratio of R1 to R2 is approximately 14 dB, the band reflection filter is connected. The optical fiber termination state determination method according to claim 1, wherein the determination step is a determination step.

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