JPH04158237A - Photopulse tester - Google Patents

Abstract

PURPOSE:To make the S/N ratio uniform by a method wherein an output of a logarithm converting part is stored when it is better than a set value of the S/N ratio, and a gain is raised or the averaging number of times is increased when it is worse than the set value, thereby to improve the S/N ratio. CONSTITUTION:Data of a logarithm converting part 8 is sent to an S/N ratio comparing means 11 and compared with a set value. The data better than the set value is sent to and stored by a data memory means 12. For the data worse than the set value, a gain of an amplifier part 6 is increased to raise the signal level and the average is added again. Logarithmic conversion of the data is conducted in the converting part 8, and the result is sent to the comparing means 11 to detect whether it is the set value of the S/N ratio. After repeating the above procedure, if the set value is not attained even when the gain of the amplifier part 6 becomes maximum, the averaging number of times of an adding/averaging part 7 is increased. Then, the data after the addition and averaging is coupled with the data stored in the means 12, thereby to form a data of the measuring waveform. Accordingly, the S/N ratio can be made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical pulse tester (hereinafter referred to as 0TDR) that increases or decreases the number of averaging additions according to the SN ratio of the output.

[Prior art] 0TDR is a method that detects failure points in optical fibers and measures loss, splice loss, etc. by sending optical pulses to optical fibers through optical directional couplers and detecting the returning light. be.

Next, the configuration of 0TDR will be explained with reference to FIG.

In FIG. 7, 1 is a timing generator, 2 is a drive circuit, 3 is a light source such as a laser, 4 is an optical directional coupler, 5 is a light receiver, 6
7 is an amplification section, 7 is an averaging processing section, 8 is a logarithmic conversion section, 9 is a display section, and 10 is an optical fiber to be measured.

In FIG. 7, a pulse current is generated in a drive circuit 2 by an electric pulse from a timing generator 1, and a light source 3 is caused to emit light. The light pulses emitted from the light source 3 pass through the optical directional coupler 4 and enter the optical fiber 10 . Return light such as backscattered light and reflected light from the optical fiber 10 is sent from the optical directional coupler 4 to the light receiver 5. The light receiver 5 converts the light into an electrical signal, and the output of the light receiver 5 is amplified by the amplifier 6, converted into a digital signal by the averaging processor 7, and averaged. The output of the average addition processing section 7 is logarithmically converted by a logarithmic conversion section 8 and displayed on a display section 9.

The backscattered light returning from the optical fiber 10 in FIG. 7 is due to Rayleigh scattering occurring within the optical fiber 10. The level of this backscattered light is about 50 dB lower than the level of the incident pulsed light when the optical fiber 10 is a normal single mode optical fiber and the width of the incident optical pulse is 1X10-6 seconds. In order to handle such minute signals, the SN can be improved by repeatedly measuring and taking the average.
Improve the ratio. The averaging processing section 7 is for this purpose, and when the quantization bit of the A/D converter is 8, there is a relationship between the number of averaging times and the S/N ratio as shown in FIG.

Data similar to FIG.
It is also described in FIG. 5 of J. In Fig. 8, for example, when the average number of times is 100 and the S/N ratio is 30 dB, 1
If we take the average of 02 times, the S/N ratio will be 110dB, which is 20dB.
B.Improved.

Next, the measured waveform of ○TDR will be explained with reference to FIG. FIG. 9 shows measurements made by connecting optical fibers IOA and IOB, with the horizontal axis representing the distance of the optical fibers and the vertical axis representing the received light level. The received light level is logarithmically converted by the logarithmic converter 8 in FIG. 7, and is shown as a straight line sloping downward to the right. Loss at the connection section appears as a step, and reflected light generated at the break point is shown as an upward discontinuous waveform. appear. When the received light level decreases, the signal-to-noise ratio deteriorates, noise is superimposed on the measurement waveform, and the waveform becomes wide, making it impossible to perform accurate measurements.

Although the SN ratio can be improved by further increasing the number of times of averaging, the measurement time increases due to averaging through repeated measurements. For example, in order to improve the S/N ratio by 20 dB as shown in Figure 8, an additional 102 averaging times are required and the time is 10 dB.
You will need twice as much.

[Problems to be Solved by the Invention] As can be seen from FIG. 8, the number of times of averaging may be reduced in areas where the SN ratio is good, and the number of times of averaging may be increased in areas where the SN ratio is poor.

This invention adds an SN ratio detection means and a storage means, and
The purpose of this invention is to provide an 0TDR that attempts to equalize the S/N ratio on a measured waveform by changing the number of times of averaging according to the ratio.

[Means for Solving the Problems] In order to achieve this object, in the present invention, the optical pulses emitted from the light source 3 are transferred from the optical directional coupler 4 to the optical fiber 1.
0, the return light from the optical fiber 10 is sent from the optical directional coupler 4 to the light receiver 5, and the output of the light receiver 5 is sent to the amplification section 6.
The average addition processing section 7 converts it into a digital signal and averages it, and the output of the average addition processing section 7 is converted into a logarithmic conversion section 8.
In the optical pulse tester, the SN ratio is set, and the output of the logarithmic converter 8 is compared with the set SN ratio, and the average addition data is stored in the optical pulse tester. When the output of the logarithmic conversion unit 8 is better than the set value of the S/N ratio, the output of the logarithm conversion unit 8 is stored in the data storage unit 12, and the output of the logarithm conversion unit 8 is set to the S/N ratio. If it is worse than the set value, increase the gain of the S increaser 6 to improve the S/N ratio, or increase the number of times of averaging in the average addition processor 7 to improve the S/N ratio of the output of the logarithmic converter 8. The data stored in the means 12 and having a good SN ratio are combined and displayed on the display section 9.

[Function] Next, the configuration of the 0TDR according to the present invention will be explained with reference to FIG. Reference numeral 11 in FIG. 1 is an SN ratio comparison means, 12 is a data storage means, and the other parts are the same as in FIG.

The data logarithmically converted by the logarithmic converter 8 is sent to the SN ratio comparing means 11 and compared with the set value of the SN ratio comparing means 11.

Data that is better than the SN ratio of the set value is stored in the data storage means 1.
If the data is worse than the SN ratio of the set value, the gain of the amplifier section 6 is further increased to raise the signal level.
Add the averages again. Then, the logarithmic conversion unit 8 performs logarithmic conversion, and sends it to the SN ratio comparison means 11, where the SN ratio of the set value is
Determine whether it is a comparison.

In the same way, data with a good SN ratio is stored in the storage means 1.
For data with a poor S/N ratio, the gain of the amplifying section 6 is further increased and the average is added. When the gain of the increasing part 6 reaches the maximum and the set value of the SN ratio is still not obtained, the number of times of averaging in the averaging processing part 7 is increased. The data after the average addition is logarithmically converted by the logarithm converter 8, and the data is stored in the data storage means 1.
2 and combine it with the stored data to create one measured waveform data.

Next, the flowchart shown in FIG. 1 will be explained with reference to FIG. 2.

In step 21, the data of the logarithmic conversion section 8 is sent to the SN comparison means 11, and in step 22, the setting value set in the SN comparison means 11 and the data sent from the logarithm conversion section 8 are compared.

If the data of the logarithmic conversion unit 8 is better than the set value,
The process proceeds to step 28, and if the data from the logarithmic conversion unit 8 is worse than the set value, the process proceeds to step 23.

In step 23, it is determined whether the gain of the amplifying section 6 is maximum. If it is the maximum, the process proceeds to step 24; if it is not the maximum, the process proceeds to step 25.

In step 25, the gain of the amplifier section 6 is increased, and in step 26
Then, the average addition processing section 7 performs average addition.

In step 27, it is determined whether to increase the number of average additions,
If the number of average additions is to be increased, the process proceeds to step 28; if the number of average additions is not to be increased, the process is to proceed to step 22.

In step 28, the data is sent to the data storage means 11,
In step 29, the sent data is stored in the data storage means 11.

In step 30, the data in the data storage means 11 are combined, and in step 31, the combined data is displayed on the display section 9.

[Example] Next, the average addition processing unit 7 adds the average of X times, and the logarithmic conversion unit 8 performs logarithmic conversion.
This will be explained using figures.

If the setting value set in the SN ratio comparison means 11 in FIG. 1 is, for example, 20 dB, and the SN ratio at point A in FIG. 3 is 20 dB, then the data to the left of point A will have an SN ratio of 20 dB or more. Therefore, data on the left side from point A is sent to the data storage means 12 and stored.

Since point B in FIG. 3 is at the same level as the noise floor, the S/N ratio is O dB. The gain is increased by 20 dB in the amplifying section 6 of FIG. 1 to increase the signal, and the average of X times is added to obtain the measured waveform of FIG. 4. Then, the data from point A to point B is sent to storage means 12 and stored.

The 0 point in FIG. 4 is at the same level as the noise floor (7) and has an S/N ratio of O dB. In order to raise the SN ratio from point 0 to 20 dB, the gain of the amplifier section 6 is increased by 20 dB in the same way as point B, and then the average of X times is added.

FIG. 5 shows this state. The data shown in FIG. 5 is sent to the data storage means 12 and stored therein.

In the data storage means 12, all of the sent data is arranged in order from the beginning to point A, from point A to point B, from point B to point 0, and from point 0 to the end, and the levels are combined into one.
The signals are combined into one waveform and displayed as shown in FIG.

[Effects of the Invention] According to the present invention, an SN ratio comparison means and a data storage means are added to the conventional ○TDR, and the number of times of averaging is changed according to the SN ratio, so that the SN ratio on the measured waveform can be made uniform. The measurement time can be shortened. In addition, these means can be realized with software and memory, so
This can be realized with a simple circuit.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the 0TDR according to the present invention, Fig. 2 is a flowchart of Fig. 1, Figs. 3 to 6 are changes in measured waveforms of the 0TDR, Fig. 7 is a block diagram of the 0TDR, and Fig. 8 9 is a diagram showing the relationship between the number of averages and the SN ratio, and FIG. 9 is a diagram showing the measured waveform of 0TDR. DESCRIPTION OF SYMBOLS 1... Timing generator, 2... Drive circuit, 3... Light source, 4... Optical directional coupler, 5... Photoreceiver, 6...Amplification section,
7...Additional averaging processing unit, 8...Logarithmic conversion unit, 9...Display unit, 10...Optical fiber to be measured, 11... ...SN ratio comparison means, 1
2...Data storage means. Agent Patent Attorney Kin Omata Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. A light pulse emitted from a light source (3) is inputted from an optical directional coupler (4) into an optical fiber (10), and the return light from the optical fiber (10) is It is sent from the coupler (4) to the photoreceiver (5), the output of the photoreceiver (5) is amplified by the amplification section (6), converted into a digital signal by the averaging processing section (7), added and averaged, and then averaged. In the optical pulse tester, the output of the addition processing section (7) is logarithmically converted by the logarithmic conversion section (8) and displayed on the display section (9). and a data storage means (12) for storing average addition data, and when the output of the logarithmic conversion section (8) is better than the set value of the SN ratio. The output of the logarithmic conversion section (8) is stored in the data storage means (12), and when the output of the logarithm conversion section (8) is worse than the set value of the SN ratio, the gain of the amplification section (6) is increased to improve the SN ratio. or by increasing the number of times of averaging in the average addition processing unit (7) and
), and combine the data stored in the data storage means (12) with a good signal-to-noise ratio to display the display section (9).
) An optical pulse tester characterized by displaying the following: