JP2674659B2 - Optical line monitoring method - Google Patents

Description

The present invention relates to an optical line monitoring method, and more particularly to an optical line monitoring method using an optical fiber pulse tester.

(Prior art)

In recent years, with the development of optical communication technology, optical fiber cable lines (hereinafter referred to as optical lines) have been laid, and optical communication has been performed through the optical lines.

If a failure such as breakage or abnormal increase in optical loss occurs in the optical line, the position must be confirmed and the optical line must be repaired. An optical fiber pulse tester (hereinafter referred to as OTDR
There is).

As shown in FIG. 5, the OTDR 1 is connected to the optical line 2 and outputs an optical pulse signal having a predetermined pulse interval to the optical line 2.
To be introduced. Then, the light intensity of the reflected light of the light pulse signal is detected, and the longitudinal state of the optical path is observed using a display tube 1a such as an oscilloscope. The horizontal axis of the graph shown in FIG. 5 represents the propagation time of the signal, and this propagation time is actually proportional to the distance of the optical fiber from the OTDR1. On the other hand, the vertical axis represents the detected light intensity of the reflected light in decibels. Then, in the portion A where the characteristics in the longitudinal direction of the optical fiber are uniform, the light intensity of the reflected light linearly decreases with respect to the propagation time as shown in the figure, and the inclination corresponds to the optical loss of the optical line. On the other hand, at the connection point or the fault point B, a pulse-like waveform indicated by C is observed by Fresnel reflection there, and the connection point or the fault point B can be easily found.

[Problems to be solved by the invention]

When applying the above optical line monitoring system to an optical fiber communication network, multiple optical fiber cables must be connected to one OTDR.
A 1xN optical switch is connected to the tip of the OTDR1 for monitoring at 1, and an optical fiber cable can be selected alternatively. FIG. 5 shows a time change profile of the light intensity of the reflected light observed in OTDR1 in this case. This fifth
A portion indicated by E in the drawing is a phenomenon caused by the optical pulse signal causing Fresnel reflection at the optical fiber switching portion of the 1 × N optical switch 11. Within the turbulent width D (hereinafter referred to as the dead zone) of the waveform of the time-varying profile of the reflected light, even if there is a failure of the optical line, not only the position of the failure point but also whether there is a failure or not. I couldn't find it. As shown in the table of FIG. 4, this dead zone differs depending on the wavelength, pulse interval, etc. of the optical pulse emitted by the OTDR1.

Therefore, it has been difficult to sufficiently monitor the optical fiber line.

Therefore, an object of the present invention is to provide an optical line monitoring method capable of monitoring whether or not there is a fault point in the optical fiber line over the entire range of the optical fiber line.

[Means for solving the problem]

In order to achieve the above-mentioned object, the optical line monitoring method of the present invention introduces an optical pulse signal from an optical fiber pulse tester into the optical line, and observes the time change profile of the light intensity of the reflected light. An optical line monitoring method for monitoring the time change profile, the data sampling step of sampling data of the time change profile, and the slope calculation for obtaining the slope of the flat portion of the time change profile from the sampling data obtained in the data sampling step. In the case of assuming that no Fresnel reflection has occurred in the optical fiber connection portion provided in the optical line, based on the step, the inclination obtained in the inclination calculation step and the data of at least one point of the flat portion of the time change profile. Estimating step for estimating the estimated time change profile and the estimation time obtained in the estimating step A step of comparing the estimated connection loss immediately before the position of the optical fiber connection portion of the change profile with the connection loss of the optical fiber connection portion measured in advance, and monitoring the state of the optical line based on the comparison result. And

[Action]

In the optical line monitoring method of the present invention, configured as described above,
The part of the time-varying profile affected by the Fresnel reflection is estimated from the condition of other parts when there is no Fresnel reflection, and the part affected by the Fresnel reflection is judged from the estimated value. It enables the monitoring of optical lines in.

〔Example〕

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

Elements denoted by the same reference numerals have the same functions, and duplicate descriptions will be omitted.

FIG. 1 shows schematic steps of the optical line monitoring method of the present invention,
FIG. 2 shows an example of an optical fiber communication network system capable of monitoring by the optical line monitoring method according to the present invention.

First, the optical fiber communication network system shown in FIG. 2 will be described.

In the optical fiber communication network system shown in FIG.
An exchange 11a is provided at 10a, and a private branch exchange 11b is installed at the building 10b.
However, another telephone station 10c is provided with an exchange 11c and the like. The optical line 20 is connected to the exchange 11a of the telephone station 10a, and the optical line 20 is connected to a private branch exchange 11b such as the building 10b and a switch 11c of another telephone station 10c via a repeater 21 and each telephone set. It is connected to communication devices such as 12a and 12b. And
In order to monitor the condition of this optical line 20, O
TDR13 is provided.

This OTDR 13 is a 1 × N optical switch 14 via an optical fiber.
The output optical fiber cables of the 1 × N optical switch 14 are connected to the optical signal multiplexer / separator 16.
The output optical fiber cables are provided corresponding to the plurality of optical fiber cables of the optical line 20, respectively. The optical signal multiplexer / separator 16 is connected to the optical line 20, introduces the optical pulse signal into the corresponding optical fiber cable selected by the 1 × N optical switch 14, and reflects the reflected light from the optical fiber cable. Separate transmission to OTDR3. OTDR1
A signal processing device 15 for signal processing the detected data is connected to 3. This signal processor 15 processes the data and monitors whether there is a fault in the optical line.

Hereinafter, a method of monitoring the presence / absence of a failure point on the optical line of the optical fiber communication network system will be described.

As shown in FIG. 1, this monitoring method is roughly divided into a sampling step 30, a moving average step 31, an inclination calculation step 32,
It comprises a time change profile estimation step 33, a loss estimation step 34 and a comparison judgment step 35.

The principle of the optical line monitoring method according to the present invention will be described.

When the optical line of the optical fiber communication network system shown in FIG. 2 is monitored using the OTDR, the time change profile shown in FIG. 3 (a) can be obtained. In FIG. 3A, the horizontal axis corresponds to the signal propagation time, and actually corresponds to the distance from the OTDR. The vertical axis represents the light intensity of the reflected light of the optical pulse signal in dB.

In the time-varying profile thus obtained, the E portion is the portion affected by the Fresnel reflection generated in the optical switch. Here, if the Fresnel reflection does not occur, the time change profile in the affected portion E of the Fresnel reflection is an extension line G of the flat portion F of the time change profile (hereinafter, this extension line G is referred to as an estimated time change profile straight line G). It is estimated that As described above with reference to FIG. 5, this utilizes the property that an optical fiber having a uniform property in the longitudinal direction has a linear time change profile. Then, the difference L between the light intensity value Gs of the reflected light of the estimated time change profile line G at the position Ea where the influence of Fresnel reflection starts and the light intensity value Es of the reflected light at this position of the actual time change profile Ask for. This L corresponds to the light loss due to this Fresnel reflection. Therefore, when the connection loss Sl of the optical switch is measured at the time of laying the optical line, and if L> Sl, it is estimated that there is some obstacle point in the optical line in the affected portion E of the Fresnel reflection. As a result, it becomes possible to monitor the optical line even in the affected part of the Fresnel reflection. On the other hand, in order to obtain the estimated time change profile line G, the time change profile is first differentiated with respect to time (variable on the horizontal axis). A graph of the differentiated values is shown in FIG. 3 (b). Next, in FIG. 3 (b), the differential value K of the portion F of which the differential value is constant is obtained, and the value (d (t _k ), t _k ) and the differential value K, the estimated time change profile straight line G
Es can be obtained by obtaining {G (t) = Kt + β} and then obtaining the value {G (Ea)} of the Ea position of the estimated time change profile line G. This Ea is shown in Fig. 3 (b).
It can also be found by finding the position where the abrupt change in the differential value shown in Fig.
It is also possible to measure the distance from the OTDR to the optical switch, etc., and then calculate it back. Then, as an example of a method for automatically carrying out the above, there is a step shown in FIG.

Hereinafter, each step shown in FIG. 1 will be specifically described.

First, in the sampling step 31, the OTDR is operated to detect the light intensity of the reflected light of the optical pulse signal introduced into the optical line. Then, the dB value of the detected light intensity is set to a predetermined time interval Δ
Detection time t _p {p = 1, 2, ...
The data d (t _p ) of the time change profile in n} are measured, and the detection time t _p and the data d (t _p ) are paired (t _p , d (t _p )) {p = 1,2, ... n} (hereinafter referred to as a sampling data group).

In the next moving average step 31, the influence of fluctuations in the sampled data due to noise or the like and fluctuations in the detection accuracy during sampling on the sampling data is removed. In this moving average step 31, the following averaging process is performed on each data value of the sampling data group obtained in the previous sampling step 30.

Here, k is a range for taking a moving average, and is selected from the obtained state of the time change profile. Further, a _p is a weighting coefficient, and this weighting coefficient a _p is normally fixed to 1. However, when the detection accuracy or noise fluctuates, a predetermined weighting is applied to the sampling data in order to remove the influence of this fluctuation. Multiply the coefficient.

The averaged data obtained by the arithmetic processing of the above equation is paired with the detection time t _p and stored as {t _p , A (t _p )}.

In the next slope calculation step 32, the averaged data {t _p , A (t _p )} obtained in the previous moving average step 31 is subjected to the calculation of the following equation to obtain the time change profile at each time t _p . Find the slope α (t _p ).

Next, a difference Δ (t _p ) between adjacent slopes of the slope α (t _p ) obtained by the above formula is calculated by the following formula.

Δ (t _p ) = α (t _{p + 1} ) −α (t _p ) ... Then, a range in which the value of Δ (t _p ) is approximated to zero is obtained, and α (t _p ) = K at that time is obtained.

This K is estimated for the slope of the flat portion (corresponding to the portion F in FIG. 33 (a)) of the time change profile.

Next, the profile estimation step 33 is performed. In the profile estimation step 33, the inclination K of the flat portion (corresponding to the portion F in FIG. 3A) of the time-varying profile obtained in the inclination calculation step 32 and an arbitrary point of the flat portion, for example, From {t _k , d (t _k )} and the function d (t _p ) = Kt (t _p ) + β of the straight line of this flat portion. And the function of this straight line is the part where the influence of Fresnel reflection appears (3rd
This corresponds to the estimated time change profile line G in the case where there is no Fresnel reflection in (corresponding to the portion E in FIG. 7A).

Next, the loss estimation step 34 is performed. This loss estimation process 34
Then, the previous profile estimation step 33 at the position of the time-varying profile (the position of Ea in FIG. 3A) immediately before the influence of Fresnel reflection appears on the time-varying profile.
The value of the function of the estimated time change profile straight line G (corresponding to Es in FIG. 3 (a)) estimated in (3) is obtained. on the other hand,
The value Gs at the time Ea of the time change profile is actually stored in advance and the loss L = Gs−Es is obtained.

Next, the comparison / determination step 35 is performed. In the comparison / judgment step 35, the difference between the estimated loss L obtained in the loss estimation step 34 and the connection loss Sl of the optical switch or the like measured in advance when the optical line is laid is calculated, and the difference is predetermined. If it is within the predetermined range, it is determined that there is no fault point in the optical line corresponding to the time change profile affected by this Fresnel reflection. However, when it is outside the predetermined range, it is determined that some trouble point exists.

In this way, it is possible to check whether or not there is a fault point or the like in the portion of the optical line corresponding to the time change profile of the portion affected by Fresnel reflection.

The present invention is not limited to the above embodiment, and various modifications can be considered.

Specifically, in the above embodiment, the detection of a fault point in the portion affected by Fresnel reflection in the optical switch portion of the optical fiber communication network system has been described, but the present invention is not limited to this case, and the relay of the optical line is performed. The same can be applied to detection of a fault point in a portion affected by Fresnel reflection occurring at a connection point. In this case, it is only necessary to limit the relay connection portion to a predetermined range and obtain the time-varying profile as described above to carry out the above method. Since the position of this relay connection part is predetermined when the optical line is laid, it is easy to limit this predetermined range.

Further, although the moving average step is carried out in the above embodiment, the sampling data may be directly used in the slope calculating step without carrying out the moving average step.

〔effect〕

In the optical line monitoring method of the present invention, as described above,
Even if there is a connecting member or the like that causes Fresnel reflection on the optical line, a failure point or the like on the optical line can be easily found and the entire range of the optical line can be monitored.

[Brief description of the drawings]

FIG. 1 is a process diagram of an embodiment of an optical line monitoring method according to the present invention, FIG. 2 is a diagram showing a configuration of an optical line communication network system to which the optical line monitoring method shown in FIG. 1 is applied, and FIG. The figure is a diagram for explaining the principle of the optical line monitoring method according to the present invention,
FIG. 4 is a table showing the pulse width of the optical pulse signal by Fresnel reflection in the test method by OTDR and the dead zone value when the wavelength of the optical pulse signal is changed. FIG. 5 is OTDR.
Figure 6 shows the monitoring status of the optical line by OTDR and Figure 6 shows OTDR.
It is a figure which shows the influence of Fresnel reflection in optical line monitoring. 13 …… OTDR, 14 …… 1 × N optical switch, 15 …… Signal processor, 16 …… Optical signal multiplexer / separator, 20 …… Optical line.

Claims (2)

(57) [Claims] 1. An optical line monitoring method for monitoring an optical line by introducing an optical pulse signal from an optical fiber pulse tester into the optical line and observing a time change profile of the light intensity of the reflected light. A data sampling step of sampling the data of the change profile, an inclination calculating step of obtaining an inclination of a flat portion of the time change profile from the sampling data obtained in the data sampling step, an inclination obtained in the inclination calculating step and the An estimation step of estimating an estimated time change profile in the case where it is assumed that Fresnel reflection does not occur in the optical fiber connection portion provided in the optical line from the data of at least one point of the flat portion of the time change profile, and the estimation step. Immediately before the position of the optical fiber splicing part of the estimated time change profile obtained in An optical line monitoring method, comprising: comparing the estimated connection loss in 1. with the connection loss of the optical fiber connection portion measured in advance, and monitoring the state of the optical line based on the comparison result. 2. The optical line monitoring method according to claim 1, wherein a moving average of the sampling data obtained in the data sampling step is obtained, and the inclination calculating step is carried out based on the moving averaged sampling data.