JPH06160197A - Pulse tester and light loss measuring method using it - Google Patents

Abstract

PURPOSE:To provide the light loss measuring method capable of measuring the light loss of a light guide path with a pulse tester and capable of reducing the work man-hours at a low cost. CONSTITUTION:The first reference reflector 3 is connected to the pulse tester mouth 2 of a pulse tester 1. The reflected wave-form of the first reference reflector 3 is measured with the pulse tester 1, and the peak value is recorded. A measurement optical fiber section 5 is connected to the pulse tester mouth 2 in place of the first reference reflector 3, then the second reference reflector 4 is connected to the light source outgoing end of the measurement optical fiber section 5. The reflected wave-form of the second reference reflector 4 is measured with the pulse tester 1, and the peak value is recorded. When the difference between the measured peak values is calculated, the light loss of the measurement optical fiber section 5 is obtained by the pulse tester 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical loss measuring method and apparatus for an optical waveguide such as an optical fiber.

[0002]

2. Description of the Related Art Conventionally, when measuring the optical loss of an optical fiber and an optical waveguide using the optical fiber, a method of using a light source and a power meter is generally used.

7 and 8 are diagrams for explaining an optical loss measuring method using a conventional optical power meter.

As shown in FIG. 7, first, as shown in FIG. 7A, the light source output at the light source opening 102 of the light source 101 is measured by the optical power meter 103, and the value is set as a reference value (0 dB). Next, as shown in FIG. 7B, the optical fiber 104 to be measured is connected to the light source port 102 (measurement point A), and the optical power meter 103 is moved to the measurement point B, which is the emission end side of the optical fiber 104 to be measured. To do. Then, the output from the light source is measured at the measurement point B.

When performing such a measurement, it is very convenient when the optical fiber 104 to be measured is wound with a bobbin or the like and the distance between the measurement point A and the measurement point B is short. However, when the optical fiber to be measured is laid, the distance between the measurement points AB inevitably increases, so that the operator moves to the measurement point B with the optical power meter 103 after the measurement at the measurement point A is completed. I have to do it. Further, since it takes time to move, the light source output may change with time.

There is a method of arranging two optical power meters as shown in FIG. 8 at the measuring point A and the measuring point B, respectively, when the two points are separated from each other. As shown in FIG. 8A, first, the light source output at the light source opening 202 of the light source 201 is measured by the first optical power meter 203. Next, as shown in FIG. 8B, the first optical power meter 2
In place of No. 03, the measured optical fiber 205 is connected to the light source port 202 (measurement point A). Then, the output from the light source is measured by the second optical power meter 204 at the measurement point B on the emission end side of the optical fiber 205 to be measured. At this time, the measured value of one is communicated to the other operator by using a communication means such as a telephone line or an optical telephone. Then, the measurement value at the measurement point A is subtracted from the measurement value at the measurement point B to obtain the loss result of the optical fiber between the two distant points. With this method, if each optical power meter is calibrated,
Measurement can be done in a short time.

By the way, when laying an optical fiber, in general, in order to measure the optical loss using the optical power meter and the light source as described above, the tendency of the abnormality and the optical loss distribution at the connection point such as the connector or the fusion is generally observed. It is known that measurement using a pulse tester is used together.

FIG. 9 is a diagram showing a control system of a conventional pulse tester. FIG. 10 is a diagram showing a result of measuring an optical fiber using a conventional pulse tester.

As shown in FIG. 10A, when an optical fiber is connected to the measured optical fiber connection port 302 of the pulse tester 301 and pulsed light is made incident on the measured optical fiber section connection port 302 and propagated, A part of the Rayleigh scattered light returns to the light source entrance end A due to the minute fluctuation of the refractive index in the core. This is called backscattered light. In addition, since there is a sharp change in the refractive index at a connection point (connector connection point C, fusion connection points D and E) of a connector or fusion and a terminal (light source emission end B) or a break point, a large reflected light (Fresnel reflection) is generated. Light) is generated. The backscattered light and the Fresnel reflected light return to the light source incident end A after a lapse of time proportional to the distance to the reflection point. The light returned in this way is separated by the optical directional coupler in the pulse tester 301 shown in FIG. 9, and then converted into an electric signal by the photoelectric converter, to obtain a waveform as shown in FIG. To be The backscattered light and Fresnel reflected light from the optical fiber can be measured based on this waveform, and the position of the fault point and the optical loss distribution of the optical fiber can be observed.

[0010]

However, as described above, the optical power meter is used for the optical loss measurement of the optical waveguide such as the optical fiber, and the optical pulse tester is not used under the present circumstances. The reason is as follows.

In FIG. 10, if the difference between the backscattered light amount a at the light source entrance end A and the backscattered light amount b at the light source exit end B is obtained, it almost indicates the optical loss of the optical fiber. But,
At the light source entrance end A, Fresnel reflection occurs due to the connector connection between the measured optical fiber connection port and the optical fiber.
The amount of backscattered light becomes higher than the actual amount, such as the amount of backscattered light a ′. Therefore, there is a problem that the actual amount of backscattered light at the light source entrance end A cannot be measured.

When an optical fiber having a different backscattering coefficient is fused and connected in the middle of the measured optical fiber portion 310, especially, a fusion point E such as between the fusion points DE shown in FIG. When the backscattering coefficient of the optical fiber on the light source emission end B side is larger than the backscattering coefficient of the optical fiber immediately before that, the splice loss is -e as shown by the waveform of the fusion point E.
It may be [dB] in some cases, and there is a problem that the connection loss is not expressed correctly. As a method for solving this problem, the measurement from the light source entrance end A and the measurement from the light source exit end B are performed, and the distance of the measured waveform from the light source exit end B is inverted as if measured from the light source entrance end A. After that, the respective measurement waveforms are combined and averaged to cancel the error due to the difference in the backscattering coefficient. However, when trying to realize this method in real time, 2
One pulse tester, data transfer means, waveform synthesis computer, etc. are required. For this reason, there is a problem that the apparatus becomes expensive and the number of work steps increases.

The present invention has been made in view of the above-mentioned problems, and an optical loss measuring method and an optical loss measuring method which can measure the optical loss of an optical waveguide by an optical pulse tester and at the same time are inexpensive and reduce the number of working steps. The purpose is to provide a device.

[0014]

The present invention for achieving the above object is an optical loss measuring method using a pulse tester equipped with a display unit for displaying the amount of backscattered light.
The standard reflector is connected to the light source emission port of the pulse tester, the light from the pulse tester is reflected by the standard reflector, and the standard reflector is used according to the content displayed on the display unit of the pulse tester at this time. Light which is determined by setting a value near the peak value of the reflected light as the first reference value, connects the optical waveguide to be measured between the light source emission port and the standard reflector, and emits light through the optical waveguide to be measured. Is reflected by the standard reflector, and a value near the peak value of the reflected light by the standard reflector is determined as the second reference value from the display content of the display section of the pulse tester at this time, and the first reference value is determined. It is a method of calculating the optical loss of the measured optical waveguide based on a reference value and a second reference value.

Further, a pulsed light source, an optical directional coupler for separating the light incident from the pulsed light source and emitted to the measured optical waveguide from the backscattered light returning from the measured optical waveguide, A pulse for displaying the optical loss characteristic according to the distance of the optical waveguide to be measured on a display unit, comprising a photoelectric converter that receives and photoelectrically converts the backscattered light separated by the optical directional coupler. In the tester, a dummy optical waveguide having a known backscattering coefficient, which is arranged between the optical directional coupler of the pulse tester and the measured optical waveguide, and an optical loss of the measured optical waveguide are obtained. Input means for inputting a parameter for calculating the optical loss of the optical waveguide to be measured from the parameter input by the input means, and the calculation result of the calculating means is displayed on the display unit. And having a shown means.

Furthermore, in the optical loss measuring method using the pulse tester described above, the optical waveguide to be measured is connected to the dummy optical waveguide of the pulse tester, and then the far end of the optical waveguide to be measured is connected. Measurement is performed by connecting a standard reflector with known return loss, and based on the measurement result, the parameter for determining the optical loss of the measured optical waveguide is input to the input means of the pulse tester and the optical loss is measured. Is a method of calculating.

[0017]

In the optical loss measuring method using the pulse tester according to the present invention, the light output emitted from the pulse tester is reflected by using the standard reflector, and the light quantity of the reflected light is measured by the pulse tester. Then, an optical waveguide to be measured is connected between the standard reflector and the pulse tester, and the amount of reflected light reflected from the standard reflector through the optical waveguide to be measured is measured by the pulse tester. . At this time, the value near the peak value of the amount of light reflected by the standard reflector when the standard reflector was first attached, and then the reflection from the standard reflector when the standard reflector was attached via the measured optical waveguide If the difference from the value near the peak value of the light quantity is obtained from the display unit,
The loss amount of the light transmitted through the measured optical waveguide can be obtained.

Further, in the pulse tester according to the present invention having the dummy optical waveguide whose backscattering coefficient is known, the optical waveguide to be measured is connected to the dummy optical waveguide when obtaining the optical loss.
As in the optical loss measuring method described above, a standard reflector is connected to the far end of the measured optical waveguide, which is the light emitting side, and the backscattered light is measured by the pulse tester. Next, the measurer reads the respective values of the backscattered light amount immediately before the dummy optical waveguide emission point and the backscattered light amount from the reference reflector from the display contents of the display unit, and the respective values, the return loss of the standard reflector and the dummy. A parameter for obtaining a light loss consisting of the backscattering coefficient of the optical waveguide is input from the input means. At this time, the content of the parameter is calculated by the calculating means, and the optical loss of the optical waveguide to be measured is calculated. Further, this optical loss measuring method requires only one measurement as compared with the above-mentioned optical loss measuring method.

[0019]

Embodiments of the present invention will now be described with reference to the drawings.

(First Embodiment) FIG. 1 is a view for explaining a first embodiment of the optical loss measuring method of the present invention. FIG. 2 is a waveform diagram showing the loss of the optical fiber according to the first embodiment of the optical loss measuring method of the present invention.

As shown in FIG. 1A, the pulse tester 1
The first standard reflector 3 is connected to the mouth 2 of the pulse tester. The reflectance of this first standard reflector 3 is calibrated to a regulation value. Further, its reflectance needs to be sufficiently larger than the reflectance of Fresnel reflection at the measured optical fiber connection port 2. This is for discriminating between the Fresnel reflection at the mouth 2 of the pulse tester and the reflection of the standard reflector to reduce the error of the Fresnel reflection component.

In this way, the pulse tester 1 is used to measure the reflection waveform of the first standard reflector 3 as shown in FIG. 2, and the peak value (or the value of the specified point near the peak) is measured.
, Or the waveform itself. The pulse tester 1 used here has a light receiving section (a light receiving element such as a photodiode, for a reflected light from a standard reflector,
(Amplification circuit, A / D converter, etc.) must be able to measure without saturation.

Then, as shown in FIG. 1 (b), instead of the first standard reflector 3, a connection point such as a connector or fusion (connector connection point C , The measured optical fiber portion 5 including the fusion points D and E) is connected, and the second standard reflector 4 is connected to the light source emission end B thereof. At this time, the reflectance of the second standard reflector 4 needs to be calibrated to a specified value, and the value is preferably the same as that of the first standard reflector 3. If the values are not the same, it is necessary to know exactly the exact reflectance of the first standard reflector 1 and the second standard reflector 3 or the ratio of the reflectances of each other.

In this way, the pulse tester 1 is used to measure the optical fiber portion 5 to be measured and the second optical fiber portion 5 as shown in FIG.
The reflection waveform of the standard reflector 4 is measured, and the peak value of the reflected light from the second standard reflector 4 (or the value of the defined point near the peak) is recorded.

The peak value of the waveform reflected by the first standard reflector 3 represents the optical power incident on the incident end of the optical fiber part to be measured. The peak value of the reflected waveform by the second standard reflector 4 is the measured optical fiber part 5 (between AB).
Shows the value after being transmitted through the optical fiber under test, reflected by the second standard reflector 4, and transmitted through the optical fiber to be measured again. Therefore, the difference between the peak values is twice the optical loss of the optical fiber under measurement. Since the pulse tester displays the round-trip optical loss, the optical loss of the optical fiber part 5 to be measured can be obtained by reading the difference between these values in the measurement waveform as shown in FIG.

As described above, by using the two standard reflectors and the pulse tester, the optical loss of the optical fiber can be accurately measured even under the influence of Fresnel reflection at the connection point. In addition, it is possible to measure the optical loss of an optical fiber only with a pulse tester without the need for a separate optical power meter to measure the optical loss as in the past, and at the same time, the loss distribution such as the position of the fault point can be measured. Can be measured.

(Second Embodiment) FIG. 3 is a view for explaining a second embodiment of the optical loss measuring method of the present invention. FIG. 4 is a waveform diagram showing the loss of the optical fiber according to the second embodiment of the optical loss measuring method of the present invention.

In this embodiment, the case where the optical fiber to be measured is a multimode optical fiber will be described.

In the multimode optical fiber, since there are many propagation modes, mode conversion occurs, and the measured value may differ depending on the incident state of light. Therefore, it is necessary to devise a constant light incident condition so that the optical power distribution of each propagation mode does not change even when propagating in the optical fiber. In order to satisfy such conditions, FIG.
As shown in, the exciter 13 for stabilizing the propagation mode is used.

As shown in FIG. 3A, the pulse tester 1
The first standard reflector 14 is connected to the mouth 12 of the pulse tester 1 through the exciter 13. This first standard reflector 13
The reflectance of is calibrated to the regulation value as in the first embodiment. In addition, the reflectance of the exciter 13 and the first
It is necessary to be sufficiently larger than the reflectance of Fresnel reflection occurring between the standard reflector 14 and the standard reflector 14.

In this way, the pulse tester 11 is used to measure the reflection waveform of the first standard reflector 14 as shown in FIG. 4, and the peak value (or the value of the specified point near the peak) is determined. Record, or record the waveform itself.

Next, as shown in FIG. 3B, the exciter 13 connected to the pulse tester 11 in place of the first standard reflector 14 is connected to a connecting point (connector connecting point) such as a connector or fusion. Optical fiber part 1 to be measured including C, fusion points D, E)
6 is connected, and the second standard reflector 15
Connect. At this time, the reflectance of the second standard reflector 15 needs to be calibrated to a specified value, and the value is preferably the same as that of the first standard reflector 14. If the values are not the same, it is necessary to know exactly the exact reflectance of the first standard reflector 14 and the second standard reflector 15 or the ratio of the reflectances of each other.

In this way, the pulse tester 11 is used to measure the reflection waveforms of the optical fiber part 16 to be measured and the second standard reflector 15 as shown in FIG. 4, and the second standard reflector 15 is measured. Record the peak value of the reflected light from (or the value at the specified point near the peak). Then, as in the first embodiment, the optical loss of the optical fiber part 5 to be measured can be obtained by reading the difference between the value obtained by the first standard reflector 14 and the value obtained by the second standard reflector 4.

As described above, the same effect as in the first embodiment can be obtained with the multimode optical fiber.

In the first and second embodiments described above,
Although the measurement is performed using two standard reflectors, the measurement is not limited to this, and only one standard reflector may be performed.

(Third Embodiment) FIG. 5 is a diagram for explaining a third embodiment of the present invention.

The pulse tester of this embodiment shown in FIG. 5A has a control system similar to that of the conventional device shown in FIG. The control system allows the light from the pulse light source 21 to pass through the optical directional coupler 22 and enter the optical fiber, and the backscattered light from the optical fiber is switched in the optical directional coupler 22 to change the direction of the photoelectric converter. 23 to receive light. Then, the received backscattered light is photoelectrically converted, and the calculation is controlled by the voltage value thereof to display the waveform of the backscattered light amount according to the distance of the optical fiber on the display tube surface of the display unit. In the present embodiment, the light entrance / exit element 22a of the directional coupler 22 of the control system is provided with a dummy fiber 24 having a known backscattering coefficient in advance, and the far end side when viewed from the end of the dummy fiber 22 of the entrance / exit element 22a. Dummy fiber 22 end of the optical fiber connection port 2 to be measured
5 is provided and configured. Further, the apparatus of the present embodiment has an input means (not shown) for inputting the parameter for obtaining the optical loss, and the control system is provided with the optical loss based on the parameter inputted by the input means. A calculation means (not shown) for calculating and a display means (not shown) for displaying the result calculated by the calculation means on the display tube surface are incorporated.

To measure the optical loss of the optical fiber, the measured optical fiber connection port 25 of the pulse tester of the present embodiment is used.
The end of the measured optical fiber 26 is connected to the measured optical fiber 26, and the measured optical fiber 26 on the far end side when viewed from the end of the measured optical fiber 26.
This is performed by connecting a reference reflector 27 having a known return loss to the end portion.

As a result of the connection and measurement as described above, a waveform diagram as shown in FIG. 5B is displayed on the display tube surface. In the apparatus of this embodiment, the measurer reads the values of the backscattered light amount Y immediately before the dummy fiber emission point from the display tube surface and the backscattered light amount X immediately after the reflection by the reference reflector, which will be described later. The optical loss of the optical fiber to be measured can be obtained by inputting the parameter for obtaining the optical loss including the value from the input means and calculating it by the calculating means.

Now, the calculation means for calculating the optical loss of the optical fiber to be measured will be described with reference to FIG.

FIG. 6 is a diagram for explaining the formula of the calculating means for obtaining the optical loss of the optical fiber to be measured in the third embodiment of the present invention.

The arrow A shown in this figure is the light source output of the pulse light source 21, the arrow a is the downward loss of the optical directional coupler, the arrow b is the upward loss of the optical directional coupler, and the arrow c is the optical loss of the dummy fiber. Reference numeral O is the backscattering coefficient of the dummy fiber, arrow d is the connection loss between the dummy fiber and the optical fiber under measurement,
The arrow f indicates the return loss of the connection point between the dummy fiber and the measured optical fiber, the arrow e indicates the optical loss of the measured optical fiber, and the arrow g indicates the return loss of the standard reflector (connection loss at the connector,
(Including reflection).

Using the above-mentioned symbols, the light reception level Y at which the backscattered light emitted from the pulse light source 21 and immediately before the emission point of the dummy fiber is received by the photoelectric converter 23 is expressed by the equation: Y = A-a-b- 2c-O ... Formula (1). Further, when the light reception level X of light emitted from the pulse light source 21 and reflected from the reference reflector attached at the far end is received by the photoelectric converter 23 is expressed by the formula, X = A−a−b−2c−2d -2e-g ... Formula (2). When the optical loss e of the optical fiber to be measured is calculated from the above equations (1) and (2), Y−X = 2d + 2e + g−O ∴d + e = (Y−X + O−g) / 2 (3) Becomes Thus, in the above formula (3), (measured optical fiber connection port loss d + measured optical fiber optical loss e)
Is the backscattered light amount Y immediately before the dummy fiber emission point read from the display tube surface, the backscattered light amount X immediately after reflection by the reference reflector, and the known dummy fiber backscattering coefficient O.
And the parameter of the return loss g in the reference reflector. That is, in the apparatus of this embodiment, the optical loss is calculated by the above equation (3) of the calculating means by inputting the above parameters by the inputting means.

In the above equation (3), the measured optical fiber connection port loss d is not separated, but the conventional method of measuring the installed optical fiber by using the optical power meter and the light source, After measuring the output of the light source opening of the light source, connect the optical fiber to be measured to the light source opening and measure the output from the far end of the optical fiber far from the light source to obtain the optical loss. Measured fiber optic splice loss is included. Therefore, even if the measured optical fiber connection loss d is included in the equation (3) for obtaining the optical loss in the present embodiment, the measurement by the device of the present embodiment is at the same level as that of the conventional optical power meter. , No problem is required.

In the present embodiment described above, the optical fiber to be measured is not required to be measured twice at the near end or far end of the pulse tester as in the configurations of the first and second embodiments. The optical loss can be obtained by measuring once.

[0046]

As described above, the present invention has the following effects.

In the method according to claim 1, the standard reflector is connected at the light source emission port of the pulse tester or the light source emission end of the optical waveguide to be measured connected to the pulse tester, and the measurement is carried out. Irrespective of factors that adversely affect the measurement such as loss error or Fresnel reflection at the incident end of the measured optical waveguide, which occurs when an optical waveguide having a different backscattering coefficient is fused in the measured optical waveguide,
The pulse tester can measure the optical loss in the measured optical waveguide. For this reason, when laying an optical fiber as in the conventional case, the optical power meter and the light source were used at the same time as the optical loss measurement, and at the same time, the measurement using the pulse tester was used to see the tendency of the optical loss distribution. It becomes possible to make these measurements only with the pulse tester.

Further, in the apparatus and the method according to claims 2 and 3, the standard is provided at the light source emission end of the optical waveguide to be measured connected to the pulse tester containing the dummy optical waveguide whose backscattering coefficient is known. By connecting the reflector and performing the measurement, the optical loss can be calculated, and at the same time, the connection of the standard reflector can be measured once. Therefore, the number of working steps can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a first embodiment of the optical loss measuring method of the present invention.

FIG. 2 is a waveform diagram showing the loss of the optical fiber according to the first embodiment of the optical loss measuring method of the present invention.

FIG. 3 is a diagram for explaining a second embodiment of the optical loss measuring method of the present invention.

FIG. 4 is a waveform diagram showing the loss of the optical fiber according to the second embodiment of the optical loss measuring method of the present invention.

FIG. 5 is a diagram for explaining a third embodiment of the optical loss measuring method of the present invention.

FIG. 6 is a diagram for explaining a formula of a calculating means for obtaining an optical loss of an optical fiber to be measured according to a third embodiment of the present invention.

FIG. 7 is a diagram for explaining an optical loss measuring method using a conventional optical power meter.

FIG. 8 is a diagram for explaining an optical loss measuring method using a conventional optical power meter.

FIG. 9 is a diagram showing a control system of a conventional pulse tester.

FIG. 10 is a diagram showing a result of measuring an optical fiber using a conventional pulse tester.

[Explanation of symbols]

 1, 11 pulse tester 2, 12 pulse tester mouth 3, 14 first standard reflector 4, 15 second standard reflector 13 exciter 16, 26 optical fiber part under test 21 pulse light source 22 optical directional coupling Device 22a Inlet / outlet 23 Photoelectric converter 24 Dummy fiber 25 Measured optical fiber connection port 27 Reference reflector

Claims (3)

[Claims] 1. A method of measuring optical loss using a pulse tester equipped with a display unit for displaying the amount of backscattered light, wherein a standard reflector is connected to a light source emission port of the pulse tester, and the pulse test is performed. The light from the device is reflected by the standard reflector, and the value near the peak value of the reflected light by the standard reflector is determined as the first reference value from the display content of the display unit of the pulse tester at this time, An optical waveguide to be measured is connected between the light source emission port and the standard reflector, and light emitted through the optical waveguide to be measured is reflected by the standard reflector, and a display of the pulse tester at this time A value near the peak value of the light reflected by the standard reflector is determined as a second reference value from the display contents of the section, and the light of the optical waveguide to be measured is determined based on the first reference value and the second reference value. Optical loss measurement method to calculate loss. 2. A pulsed light source, and an optical directional coupler for separating the light incident from the pulsed light source and emitted to the measured optical waveguide from the backscattered light returning from the measured optical waveguide. A pulse for displaying the optical loss characteristic according to the distance of the optical waveguide to be measured on a display unit, comprising a photoelectric converter that receives and photoelectrically converts the backscattered light separated by the optical directional coupler. In the tester, a dummy optical waveguide having a known backscattering coefficient, which is disposed between the optical directional coupler of the pulse tester and the measured optical waveguide, and an optical loss of the measured optical waveguide are obtained. Input means for inputting parameters for calculating the optical loss of the optical waveguide to be measured from the parameters input by the input means, and a table for displaying the calculation result of the calculating means on the display section. And a pulse tester. 3. An optical loss measuring method using the pulse tester according to claim 2, wherein the measured optical waveguide is connected to a dummy optical waveguide of the pulse tester, and then the measured optical waveguide of the measured optical waveguide is connected. Measurement is performed by connecting a standard reflector with known return loss to the far end, and based on the measurement results, input the parameters for determining the optical loss of the measured optical waveguide to the input means of the pulse tester. Optical loss measurement method to calculate optical loss.