JPH08105817A - Optical waveguide tester for detecting connector type connection point and terminal or breaking point using highly sensitive quadratic differentiator - Google Patents

Abstract

PURPOSE: To make possible highly reliable detection without being affected by noises or the like by a method wherein a light pulse emitted at a specified time interval is applied to an optical waveguide to be tested and back scattered light is converted into an electric device signal to judge whether an output wave from a quadratic differentiator is a Fresnel reflected wave or not. CONSTITUTION: A quadratic differentiator operated with a template is prepared to discriminate Fresnel reflection and a fused type connection point automatically. From the quadratic differentiator, an optical pulse reflects on an end face of an optical fiber at a connector type connection point, on a breaking surface, at a termination or the like and hence, a square waveform is formed. The template allows favorable reaction to a Fresnel reflected wave rising in a pulse to obtain quadratic differentiation waves ΔP and -ΔP in opposite polarity to each other at the falling part of the Fresnel reflected wave. The differentiation waves ΔP and -ΔP are generated at the rising and falling parts of the Fresnel reflected wave, the interval corresponds to the width of the optical pulse applied to an optical waveguide to be tested and can be specified as a Fresnel reflection point with a waveform judging device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly sensitive second-order differentiator capable of accurately detecting a changing point of an analog signal having a sharp rise and a fall, and a second-order differentiator outputted from the second-order differentiator. The present invention relates to a waveform judgment device for judging a waveform and an optical waveguide test device using these devices.

[0002]

2. Description of the Related Art A conventional optical waveguide test apparatus is shown in FIG.
The optical pulse from the optical pulse generator 11 is an optical directional coupler 1.
It is incident on the optical waveguide 13 to be tested via 2. An optical fiber is generally considered as the optical waveguide 13 to be tested. The backscattered light returning from the optical waveguide 13 under test is incident on the opto-electric converter 14 via the optical directional coupler 12 and converted into an electric signal.

This electric signal is converted into a digital signal by an A / D converter 15, the digital signal is averaged by an adder (average) 16 to improve S / N, and a logarithmic converter 17 is provided. Is logarithmically converted and displayed on the display unit 18. When the length of the optical waveguide 13 to be tested is L and the loss of the optical fiber per unit length is α, the level of backscattered light is proportional to exp (−2αL). The loss-to-distance characteristics displayed on the display 18 are as shown in FIGS. 9 and 10. The characteristics shown in FIG. 9 show the case where the optical waveguide 13 under test has the fusion splicing point A. The characteristics shown in FIG. 10 show the case where the connector type connection point C is provided.

That is, at the fusion splicing point A of the optical fiber, a loss larger than the loss of the optical fiber occurs. The occurrence of this loss is represented by the difference in the inclination angle of the propagation characteristics. At the connector-type connection point C, reflection occurs at the end face of the optical fiber forming the optical waveguide 13 under test. Since this reflection is superposed on the backscattered light and returns, a pulsed detection waveform with a relatively high level is observed.

[0005]

In the optical waveguide test apparatus of this type, the position of the fusion splicing point of the optical fiber and the amount of attenuation of the backscattered light are accurately determined by the invention of Japanese Patent Application No. 1-4456. Although detected, the operator performs the connector type connection and the discrimination of the termination or the disconnection point.
For this reason, there is a drawback in that the measured value varies from person to person and the accuracy is poor.

At the connector type connection point, the waveform of the backscattered light is shown in FIG.
It becomes a rectangular wave like. This rectangular wave-like reflection will be referred to as a Fresnel reflected wave below. Since the position of the rising point of this Fresnel reflected wave indicates the connection point, the break point and the end point of the optical waveguide, it is possible to accurately detect the position of the connector type connection point, the break point and the end point by measuring this. However, another determination means is required to distinguish these.

Here, the reason why the Fresnel reflected wave is generated will be described. When a light pulse is incident on the optical waveguide and its backscattered light is measured, the attenuation characteristics of the backscattered light as shown in FIGS. 9 and 10 are obtained. The Fresnel reflected wave mentioned here refers to a wave within a section T of steep rising and falling in FIGS. 4A, 5A, and 6A. When the time is obtained from the distance corresponding to this section T and the propagation velocity of light, it is approximated to the pulse width of the optical pulse incident on the optical waveguide.

To shorten the Fresnel reflected wave generation period T, the pulse width of the optical pulse may be shortened, but there is a limit to this. The pulse width of the normal light pulse is selected to be about 200 nanoseconds. Also, since the waveforms at the connector type connection point C and the terminal ends B (FIG. 9) and D (FIG. 10) of the optical waveguide are similar, if the connector type connection point C exists near the terminal end B, it may be a terminal type connection. It is difficult to determine whether it is point C or not.

Also, when a break occurs near the end, it is difficult to determine whether it is the connector type connection point, the end, or the break failure. An object of the present invention is to output from a high-sensitivity second-order differentiator capable of obtaining a second-order derivative signal having a large level by changing the waveform relatively steeply at connector-type connection points, break points, and termination positions. We propose to determine the Fresnel reflection wave from the waveform and detect the connector type connection point and termination or break point, and to provide an optical waveguide test device that can perform automatic measurement using these devices. To do.

[0010]

The first invention of this application corresponds to the first detecting means for sequentially detecting the value of the input analog signal and the Fresnel reflected wave generation period of the analog signal from the first detecting means. Second detecting means for detecting the value of the signal at the position delayed by the distance, and third detecting means for detecting the value of the signal at the position further delayed by the distance corresponding to the Fresnel reflected wave generation period from the detected position of the second detecting means. Detecting means, first
Addition means for obtaining the sum of the detection results of the detection means and the third detection means, and a doubled value of the detection result of the second detection means is subtracted from the addition result of the addition means, and a secondary differential signal of the analog signal is output. A high-sensitivity second-order differentiator is constituted by the subtraction means, and the second-order derivative output output from the high-sensitivity second-order differentiator has differential signals of opposite polarities at positions separated by a distance corresponding to the Fresnel reflected wave generation period. When the detecting means for detecting the output and the differential signals having mutually opposite polarities are detected by the detecting means at the distance corresponding to the Fresnel reflected wave generation period, the position is determined to be the end face of the optical waveguide under test. An optical waveguide test apparatus including a determination means is proposed.

In the second invention of this application, in the optical waveguide test apparatus proposed in the first invention, there is no noise of a specified amplitude or more after the time when the outputs of the high-sensitivity second-order differentiator generate differential signals of opposite polarities. We propose an optical waveguide testing device that detects this and identifies the connector type connection point. In the third invention of this application, in the optical waveguide test apparatus proposed in the first invention, it is confirmed that noise having a specified amplitude or more is present after the time point when the outputs of the high-sensitivity second-order differentiator generate differential signals of opposite polarities. We propose an optical waveguide tester that detects and identifies the end of an optical waveguide.

As a result, it is possible to provide an optical waveguide test apparatus capable of accurately and automatically determining a connector type connection point, a termination point or a break point.

[0013]

FIG. 1 shows an embodiment of the high-sensitivity quadratic differential device proposed in the first invention of this application. In the figure, 100 indicates the high-sensitivity second-order differentiator proposed in the first invention of this application. The high-sensitivity second-order differentiator proposed in the first invention is input from the first detection means 103 that sequentially detects the value of the analog input signal input to the input terminal 101, and from the detection time point of this first detection means 103. Second, detecting the value of the signal at a position separated by a distance corresponding to the Fresnel reflected wave generation period of the analog signal
The detection means 104, the third detection means 105 for detecting the value of the signal at a position further away from the detection position of the second detection means by the distance corresponding to the Fresnel reflected wave generation period of the input analog signal, and the first detection means. 103 and third detection means 105
And a subtraction for subtracting the double value 2N of the detection result of the second detection means 104 from the addition result M of the addition means 108 and outputting the second derivative signal of the input analog signal. And means 111.

In this embodiment, the analog signal input to the input terminal 101 is AD-converted by the AD converter 102, and the AD-converted output is input to the high sensitivity second derivative device 100. Therefore, in this example, the high-sensitivity second-order differentiating device 100 is constituted by a digital circuit.
That is, the first detection means 103 can be configured by, for example, a data latch circuit, and repeats the latch operation in synchronization with the AD converter 102 and the clock CLK. Therefore, the first detection means 103 latches the output signal every time the AD converter 102 outputs the AD converted signal.

The latch output of the first detecting means 103 is given to the second detecting means 104 and the adding means 108. The second detection means 104 is, for example, a delay means 1 such as a shift register.
04A and the data latch circuit 104B. The delay unit 104A delays the input signal by a time corresponding to the Fresnel reflected wave generation period of the input analog signal. That is, the Fresnel reflected wave generation period T at the connector type connection point corresponds to the pulse width of the optical pulse. As a result, the delay amount D of the digital delay means 104A having the AD conversion cycle as T _AD and the pulse width of the optical pulse as W _L is defined by D = W _L / T _AD . That is, the number of AD conversions during the Fresnel reflected wave generation period corresponds to the delay amount D.

Therefore, if the Fresnel reflected wave generation period corresponds to, for example, five AD conversion operations, the delay means 1
As the shift register forming 04A, a 5-stage shift register may be used. AD delayed by the delay unit 104A
The converted data is taken out by the data latch 104B, and the latch output is the third detection means 105 and the doubling operation means 109.
Given to.

The third detecting means 105 is the second detecting means 104.
Similarly to the delay means 105A and the data latch circuit 105B
It can be configured by and. Third detection means 105
The delay amount of the delay unit 105A that constitutes the
The same as the delay amount of the delay unit 104A of No. 04, the number of AD conversions in the pulse width of the optical pulse is taken, the delayed output is latched by the data latch circuit 105B, and the latch output is given to the adding unit 108.

In the adding means 108, the AD conversion data detected by the first detecting means 103 and the A detected by the third detecting means are detected.
An operation of adding the D conversion data is performed. On the other hand, the AD conversion data detected by the second detection means 104 is the doubling operation means 1
It is converted to a doubled value at 09 and sent to the subtraction means 111.
The subtracting means 111 subtracts the double value calculated by the double value calculating means 109 from the added value added by the adding means 108, and the result K
Get.

As a result, K is continuously obtained for each AD conversion operation and becomes a secondary differential output extracted with high sensitivity from the Fresnel reflection waveform. The reason for high sensitivity will be described below. Generally, the second derivative operation is performed by the following equation. f ″ _(x) = d ² f / dx ² = f _(x-1) + f _{(x + 1)} -2f _(x) (1) When AD conversion data is applied to this quadratic differential equation, AD
It is equivalent to adding the data values (N-1) (N + 1) before and after the conversion number N as they are, and subtracting the value obtained by doubling the data value of the number N from this added value.

This arithmetic processing format will be referred to as a template shown in FIG. To realize this template, delay means 104A and 105A in the circuit configuration shown in FIG. 1 are used.
Should be set to each one delay amount.
FIG. 3 shows an embodiment of the optical waveguide test apparatus proposed in the second and third inventions of this application. In the embodiment shown in FIG. 3, parts corresponding to those of the conventional optical waveguide test apparatus shown in FIG. 8 are designated by the same reference numerals.

The first invention of this application is an optical waveguide test apparatus capable of automatically discriminating between a fusion splicing point and a Fresnel reflection occurring at a connector type splicing point or an end or break point of an optical waveguide. Is proposed. For this purpose, a second-order differentiator 400 operating with the template shown in FIG. 2 is prepared as a second-order differentiator.

A second-order differentiator 40 operating on the template
0 (see FIG. 3) is provided. Hereinafter, this second-order differentiator will be simply referred to as the second-order differentiator 400. According to the second-order differentiator 400 that operates on the template, a rectangular waveform is generated because the optical pulse is reflected at the end face of the optical fiber at the connector type connection point, the fracture surface, the terminal end, or the like.
When this Fresnel reflected wave is passed through the second-order differentiator 400 having a template, the second-order differentiator 400 responds well in the portion of the Fresnel reflected wave to generate a second-order derivative pulse with a large output. This second derivative waveform is shown in FIG. 4B.

That is, according to the template, since the difference between the central sample point and the sample points on both sides of the sample point is obtained using the data of three sample points adjacent to each other by one sample, the Fresnel reflected wave rising in a pulse shape. , And second-order differential waves ΔP and −ΔP of opposite polarities are obtained at the trailing edge of the Fresnel reflected wave, as shown in FIG. 4B. The second derivative waves ΔP and −ΔP are generated at the rising and falling portions of the Fresnel reflected wave, and this interval approximately corresponds to the pulse width of the optical pulse given to the optical waveguide under test.

Therefore, the waveform is inputted to the waveform judging device 300 outputted from the second derivative device 400, and the waveform judging device 30 is inputted.
By 0, it is detected that the secondary differential pulses ΔP and −ΔP having mutually opposite polarities are generated at positions separated by a distance corresponding to the pulse width of the optical pulse, and the Fresnel reflection point is specified. The result is displayed on the display 18 and is also stored in a storage device or the like and taken in as one data of many optical waveguides.

The first invention distinguishes Fresnel reflection from fusion splicing connection points. On the other hand, the second invention and the third invention propose an optical waveguide test apparatus for discriminating between the connector type connection point and the termination or break point of the optical waveguide in the Fresnel reflection. In the second invention, an optical waveguide test device for detecting that there is no noise having an amplitude equal to or more than a specified amplitude on the far side from the position where the Fresnel reflection is detected, and for identifying the Fresnel reflection point as a connector type connection point by this detection Make up.

In the third aspect of the invention, it is detected that noise having a prescribed amplitude or more is present on the far side from the position where the Fresnel reflection is detected, and this detection indicates that the Fresnel reflection point is the end or break point of the optical waveguide. This is a configuration of an optical waveguide test device for determination. That is, the Fresnel reflection waveform at the connector type connection point becomes as shown in FIG. 5A,
This second derivative waveform is as shown in FIG.

On the other hand, FIG. 6A shows the Fresnel reflection waveform at the terminal or break point of the optical waveguide, and FIG. B shows the second derivative waveform thereof. Comparing FIG. 5A and FIG. 6A, the waveform data DA (X + TW) of the backscattered light is obtained at the connector type connection point because the optical waveguide exists on the far side from the connection point X.
Are maintained above a predetermined value.

On the other hand, at the end or break point of the optical waveguide, since the optical waveguide does not exist farther from the Fresnel reflection point, the backscattered light waveform data DA (X + TW) -becomes below a specified value, for example, -20 dB or less. Further, at the connector type connection point, although the second-order differential waveform on the far side from the connection point causes some noise immediately after the reflection point, the amplitude of the noise is not large.

On the other hand, at the terminal or break point of the optical waveguide, large noise is generated in the second-order differential waveform on the far side from the Fresnel reflection point. Therefore, it is possible to determine whether it is the connector type connection point or the termination (including the break point) by distinguishing these waveforms. These determinations are performed by the waveform determination device 300. FIG. 7 shows a flowchart for explaining the operation of the determination device used in the second invention and the third invention.

Waveform data DA of backscattered light in steps
(X) is captured. Waveform data DA in steps
Second Differentiation Device 4 Operating (X) by Template
Second-order differentiation is performed at 00 to obtain a differential output Y (X). In step, find the difference of the second derivative output for each adjacent sample point,
Whether or not this difference is Y (X) -Y (X + 1)> 3 is repeatedly executed by searching step and. This search detects a portion where the differential output Y (X) has a steep rise. When a steep rising portion is detected, the process branches to a step.

In the step, the standard deviation SD1 of the second-order differential data of the region (X + TW) to (X + TW + 10) apart from the position where the steep rising portion is detected by the pulse width TW or more of the optical pulse is obtained. In the example of the figure, a case is shown in which the standard deviation for 10 samples is obtained from a position separated by a distance corresponding to the pulse width TW of the optical pulse. In the step, the sample point (X-11) on the near side from the steep rising part
The standard deviation SD2 of the second derivative data of (X-1) is calculated.

In a step where the rising edge is steep, that is, the standard deviation SD1 on the far side of the Fresnel reflection point is SD1> 10 or more than the specified value, and the standard deviation SD2 on the front side is SD2 <10 ⁻¹ or less than the specified value. That is, waveform data DA (X-1) of backscattered light on the front side of the Fresnel reflection point
Is DA (X-1)>-20 (dB), and the waveform data DA (X +) of the backscattered light on the far side from the Fresnel reflection point.
When all the conditions that TW) is DA (X + TW) <− 20 (dB) are met, it is determined as the termination or break point of the optical waveguide.

In the step, both the standard deviation SD1 on the far side and the standard deviation SD2 on the front side of the Fresnel reflection point are SD1.
<10 ⁻¹ and SD2 <10 ⁻¹ , and the back-scattered light waveform data DA (X
-1) and DA (X + TW) are both DA (X-1)>-2
When all the conditions of 0 (dB) and DA (X + TW)>-20 (dB) are met, it is determined to be a connector type connection point.

[0034]

As described above, according to the first invention of the present application, it is possible to obtain a high-sensitivity second-order differentiator capable of extracting a change in Fresnel reflection waveform having a steep rise and a fall with high sensitivity. it can. Therefore, by using this high-sensitivity second-order differentiator, the presence of the connector type connection point and the termination or break point of the optical waveguide can be detected reliably without being affected by noise or the like.

Further, according to the second and third inventions of this application, it is possible to generate a unique waveform at the connector type connection point and the termination or break point of the optical waveguide from the second derivative waveform. The positions of the three points can be accurately measured from the result of the waveform determination. Therefore, the effect is remarkable when it is used for automatically testing an optical cable in which several tens to several hundreds of optical fibers are bundled.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of a first invention of this application.

FIG. 2 is a diagram for explaining the concept of the template used in the first invention.

FIG. 3 is a block diagram showing an embodiment of the first invention to the third invention of this application.

FIG. 4 is a waveform diagram for explaining the operation of the first invention of this application.

FIG. 5 is a waveform diagram for explaining the operation of the second invention and the third invention of this application.

FIG. 6 is a waveform diagram for explaining the operation of the second invention and the third invention of this application.

FIG. 7 is a flowchart for explaining the operation of the second invention and the third invention.

FIG. 8 is a block diagram for explaining a conventional technique.

FIG. 9 is a waveform diagram for explaining the operation of the conventional technique.

FIG. 10 is a waveform chart for explaining the operation of the conventional technique.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuzo Takahashi 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Kuji Yanagawa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Takao Sakurai 1-32-1 Asahicho, Nerima-ku, Tokyo Inside Advantest Co., Ltd.

Claims (3)

[Claims] 1. A. First Embodiment A first detecting means for sequentially detecting the value of the input analog signal; and B. Second detecting means for detecting the value of the signal at a position delayed by a distance corresponding to the Fresnel reflected wave generation period of the analog signal from the detection position of the first detecting means; D. third detecting means for detecting the value of the signal at a position further delayed by the distance corresponding to the Fresnel reflected wave generation period from the detection position of the second detecting means; An addition means for obtaining the sum of the detection results of the first detection means and the third detection means, and E. A high-sensitivity second-order differentiating device configured by subtracting means for subtracting a doubled value of the detection result of the second detecting means from the addition result of the adding means and outputting a second-order differential signal of the analog signal; ． An optical pulse emitted at a predetermined time interval is given to the optical waveguide under test, the backscattered light reflected by the optical waveguide under test and returned is converted into an electric signal, and this electric signal is given to the high sensitivity second derivative device. Detecting means for detecting that differential signals output from the secondary differentiating device are separated by a distance corresponding to the pulse width of the optical pulse and differential signals having opposite polarities are output. An optical waveguide provided with a determining means for determining that the differential signals of opposite polarities are detected by the detecting means at positions separated by a distance corresponding to the Fresnel reflected wave generation distance. Test equipment. 2. The optical waveguide test apparatus according to claim 1, wherein it is detected that there is no noise of a specified amplitude or more on the far side from the position where the outputs of the secondary differentiator generate differential signals of mutually opposite polarities. An optical waveguide test device that identifies a connection point. 3. The optical waveguide test apparatus according to claim 1, wherein it is detected that noise having a predetermined amplitude or more exists on the far side from the position where the outputs of the secondary differentiator generate differential signals having polarities opposite to each other, An optical waveguide test device that identifies the end or break point of an optical waveguide.