JP2001305017A - Optical pulse testing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the measuring time by reducing the measuring frequency when obtaining a measurement waveform of loss characteristics of an optical fiber with a prescribed accuracy. SOLUTION: An optical pulse generating part 10 repeatedly generates optical pulses of a prescribed wavelength at prescribed intervals. A return light detecting part 20 allows the optical pulses from the optical pulse generation part 10 to be incident on the optical fiber 1, detects the return light, and converts it into electric signals. A waveform processing part 30 forms a measurement waveform expressing the loss characteristics of the optical fiber from the detection signal from the return light detecting part 20. In this case, a divided movement average part 50 further divides the measured waveform added and averaged by an averaging circuit 302 and converted into logarithm by a logarithmic conversion circuit 304 into a plurality of regions according to the SN ratio, and moving-averages each point in the respective regions along the waveforms. As a result, the SN ratio of the measured waveform is improved so that the waveform in the distal part becomes clearer compared with that processed only by the adding average and the result is displayed on the display 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pulse tester, and more particularly, to an optical pulse tester for testing an optical fiber used for, for example, optical communication.

[0002]

2. Description of the Related Art As a measuring device for detecting a transmission loss characteristic of an optical fiber or a connection point thereof or a deteriorated portion such as a break point, a so-called OTDR (optical time) which detects and measures its backscattered light and reflected light. domain r
An optical pulse tester called an eflectometer is known.

Conventionally, as an optical pulse tester as described above, for example, as shown in FIG. 10, an optical pulse is repeatedly input from one end of an optical fiber 1 at a predetermined timing and return light thereof is detected. In some cases, the results are averaged for the number of light pulse repetitions and displayed. In this figure, an optical pulse generator 10 is a part that repeatedly generates an optical pulse at a predetermined interval a predetermined number of times. A timing generation circuit 102 that generates a signal of the generation timing and the detection timing, and a timing signal It includes a driving circuit 104 that generates a driving signal in response to the driving signal, and a light source 106 such as a laser that generates an optical pulse having a predetermined wavelength in response to the driving signal. The return light detector 20 is a part that receives an optical pulse from the optical pulse generator 10 from one end of the optical fiber 1 and detects the return light, and is formed by an optical switch or a semi-transmissive mirror. It includes an optical directional coupler 202, a photodetector 204 such as an avalanche photodiode that detects the returned light and converts it into an electric signal, and an amplifier 206 that amplifies the resulting signal. The waveform processing unit 30 is a unit that samples a detection signal from the return light detection unit 20 and forms a measurement waveform representing the loss characteristic of the optical fiber 1. The amplifier 206 responds to the timing signal from the timing generation circuit 102. An averaging circuit 302 that samples the detection signal from the averaging circuit and adds and averages the result by the number of repetitions of the optical pulse, a logarithmic conversion circuit 304 that logarithmically converts the processing result to form a loss waveform falling to the right. including. The display unit 40 displays a measured waveform formed by the waveform processing unit 30 on a CRT (cat).
display device such as a hode ray tube).

In such a configuration, an optical pulse having a predetermined wavelength from the light source 106 is incident from one end of the optical fiber 1 via the directional coupler 202. Optical fiber 1
A part of the light pulse incident on the core is scattered backward due to the non-uniform distribution of the refractive index of the core or the like, or is reflected by the connection part or the deteriorated part and returns to the incident end. The light returning to the incident end is detected by the light receiver 204 via the directional coupler 202, and is converted into an electric signal corresponding to the intensity of the detected light. The resulting signal is amplified by the amplifier 206 and supplied to the averaging circuit 302.
The averaging circuit 302 samples the detection signal from the amplifier 206 in response to the timing signal from the timing generator 102, and forms a measurement waveform of a loss characteristic according to the distance of the optical fiber from the result.

In this case, the signal level of the return light has a value several tens of decibels lower than the intensity of the incident light pulse, and the return light has a minute value containing more noise components toward the far end of the optical fiber 1. In order to handle such minute values, the measurement from the incidence of the light pulse to the detection of the return light is repeated, and the results of the sampling are added and averaged by the averaging circuit 302 to obtain an SN (signal to noise).
Improve the ratio. As a result, the result of the addition and averaging by the averaging processing circuit 302 to improve the SN ratio is displayed on the display device 40 such as a CRT as a measurement waveform representing the loss characteristic of the optical fiber.

[0006]

However, in the above-described conventional technique, the measurement is repeated, and the averaged result is averaged by the averaging circuit 302 to display a measured waveform resulting from the improvement of the SN ratio. Therefore, it is necessary to repeat a large number of measurements before obtaining a measurement waveform with desired accuracy, and there has been a problem that the measurement time becomes long. For example, if the length of the optical fiber is several tens km to 100
With a length of about km, in order to remove a noise component on the far end side and obtain an accurate measurement waveform, for example, 2 ¹⁵
It was necessary to repeat ~ 2 ²⁰ measurements.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an optical pulse tester capable of reducing the number of measurements to obtain a waveform with desired accuracy and shortening the measurement time. The purpose is to:

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an optical pulse tester according to the present invention applies a predetermined optical pulse to one end of an optical fiber to be tested from an optical fiber to be tested. An optical pulse tester for measuring a signal level and testing a loss characteristic of an optical fiber, comprising: an optical pulse generating means for generating a predetermined optical pulse by repeating a predetermined number of times at a desired interval; Return light detecting means for detecting a return light from a pulse incident on an optical fiber and converting the light into an electric signal, and a measurement waveform representing a loss characteristic according to a distance of the optical fiber based on a detection signal from the return light detecting means. And a display means for displaying the measured waveform formed by the waveform processing means. The waveform processing means supports the detection signal from the return light detection means at a predetermined timing. And pulling, and averaging means for forming the arithmetic mean was measured waveform in accordance with the number of repetitions of light pulses in the optical pulse generating means, respectively, were set the measurement waveform formed by averaging means beforehand SN
Divided moving average means for dividing into a plurality of regions based on the ratio, and performing a moving average process using a plurality of data along the waveform for each point of the waveform for each region. .

In this case, the waveform processing means includes logarithmic conversion means for performing logarithmic conversion of each value of the processing result from the averaging processing means, and the divided moving average means includes respective logarithmic conversion results obtained by the logarithmic conversion means. Division range setting means for dividing the area by comparing whether or not the value is within a preset SN ratio range, and as the SN ratio of each point of the area divided by the division range setting means decreases, It is advantageous to include a moving average calculating means for calculating by increasing the number of data used for the moving average, and a storage means for synthesizing and storing the results processed for each area by the moving average calculating means.

Further, the optical pulse tester according to the present invention includes gain adjusting means for adjusting the number of times of averaging or the detection gain of the return light based on the processing result of the measurement waveform formed by the averaging processing means, The means may be configured to further perform a divided moving average processing on the measurement waveform from the averaging processing means after the adjustment by the gain adjusting means.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an optical pulse tester according to the present invention.
FIG. 1 shows an embodiment of an optical pulse tester according to the present invention. The optical pulse tester according to the present embodiment emits a light pulse having a predetermined wavelength from one end of the optical fiber 1 to be tested, and backscatters and reflects the light inside the optical fiber 1 at one end. This is a measuring device that detects and outputs a measurement waveform representing the loss characteristic of the optical fiber 1 from the detection result. In particular, in the present embodiment, when processing the measured waveform, the waveform that is repeatedly measured and added and averaged is further divided into a plurality of regions in accordance with an SN (signal to noise) ratio. The main feature is that a divided moving average processing unit 50 for performing moving average processing is provided. In FIG. 1, FIG.
The same parts as those shown in FIG.

That is, as shown in FIG. 1, the optical pulse tester according to the present embodiment includes an optical pulse generator 10, a return light detector 20, a waveform processor 30, and a display unit 40. The optical pulse generation unit 10 includes a timing generation circuit 102, a drive circuit 104,
A light source 106 at a predetermined timing.
6 is an optical pulse generating means which generates an optical pulse of a predetermined wavelength by driving the same and repeats this at a desired interval a predetermined number of times. For example, in the present embodiment, the number of light pulse occurrences is 2 ⁿ
It is advantageous to be able to increase or decrease each time (n is a natural number). The generated optical pulse is incident on the optical fiber 1 to be tested via the optical directional coupler 202 of the return light detector 20.

The return light detector 20 includes an optical directional coupler 202, a light receiver 204, and an amplifier 206, as in the portion shown in FIG. 10, and transmits an optical pulse from the optical pulse generator 10 to an optical fiber. Return light detecting means for supplying light from one end of the optical fiber 1 to the light receiver 204 via the optical directional coupler 202 to detect light that is backscattered or reflected back from the inside of the optical fiber 1 to the one end of the optical fiber 1 It is. The return light detected by the light receiver 204 is converted into an electric signal, amplified by the amplifier 206, and supplied to the averaging circuit 302 of the waveform processing unit 30.

The waveform processing section 30 includes an averaging processing circuit 302 and a logarithmic conversion circuit 306 similar to those shown in FIG. 10, and further includes a divided moving average processing section 50 unique to the present embodiment. Have. The averaging circuit 302
A waveform forming circuit that samples a detection signal of the return light detected by the return light detection unit and forms a measurement waveform representing the loss characteristic of the optical fiber; And an arithmetic processing circuit for adding the number of repetitions of the light pulse in the light source 106 to obtain an average value.
The processing result is supplied to the logarithmic conversion circuit 304.

The logarithmic conversion circuit 304 is an arithmetic circuit for logarithmically converting the signal level of the waveform formed by the averaging process. The result of the logarithmic conversion is a substantially right-downward linear curve proportional to the loss characteristic of the optical fiber 1. And is supplied to the divided moving average processing unit 50. In this case, the formed waveform has a lower S / N ratio toward the far end, and has a wider width including more noise components.

The divided moving average processing section 50 divides the waveform from the logarithmic conversion circuit 304 according to a preset S / N ratio, and performs a moving average along the waveform at each point of the waveform for each region. This is a waveform processing circuit. In the present embodiment, in particular, in the region on the far end side where the SN ratio becomes lower, the number of data used for the moving average is increased.
For example, a moving average using 2 ⁿ (n is a natural number) data improves the SN ratio of 5 × log1 / ｌｏ (2 ⁿ ). In the present embodiment, processing is performed by increasing the value of n in the divided region as the SN ratio becomes lower, that is, as the position approaches the far end of the waveform. In the above formula, when n is 2, -0.
75dB, S increases by 0.75dB every time the value of n increases by 1.
The N ratio is improved.

More specifically, as shown in FIG. 1, the divided moving flat processing unit 50 of the present embodiment includes an SN range comparison circuit 30.
6, a moving average circuit 308, and a storage circuit 310. The SN range comparison circuit 306 is division range setting means for performing region division by comparing whether or not each value of the waveform obtained as a result of logarithmic conversion by the logarithmic conversion circuit 304 is within a predetermined SN ratio range. In the present embodiment, for example, the area A in which the SN ratio is 20 dB or more,
Region B in the range up to 9.25 dB or more, and 1 from less than 19.25 dB
Region C in the range up to 8.5dB or more, and from less than 18.5dB to 17.75
A region D in a range up to dB or more, and E, F, G. . .
And set the range by dividing by 0.75dB. To be precise, S
Since the N ratio is represented by the relative value of the noise level at the far end point and the signal level of the detection signal, in the present embodiment, the level value of the detection signal is compared with the above set value, and the comparison result is used as the moving average. The signal is supplied to the circuit 308.

The moving average circuit 308 is an arithmetic processing circuit that performs a moving average operation on each point of the waveform supplied via the SN range comparison circuit 306. In this embodiment, the moving average circuit 308
The areas A, B,
C. . . 2 ^0, 2 ^1, 2 ^2, the number of data used in the running average as the region of the far-end side SN ratio is as low as. . Process by increasing the number so that 2 ⁿ is obtained. More specifically, for example, in the region A having a relatively high SN ratio of 20 dB or more, those values are sent directly to the storage circuit 310, and for each point in the region B, the immediately preceding value and the value of the own point are compared. , A moving average using two pieces of data to obtain the value of the own point by adding and averaging the values of the own point. A moving average using the data is taken. Similarly, the moving average with eight data by averaging the runner in the region D and the value of the previous seven, that takes a moving average using two ^three data, in the region E 2 ⁴
Moving average using the data of the following number, the following regions F, G. . . Then, the number of data to be used for the moving average is increased by twice the previous area. The result of the moving average processing is stored in the storage circuit 310.

The storage circuit 310 is a storage unit for storing the processing results of the respective regions from the moving average circuit 308, and combines the stored waveforms of the respective regions and supplies them to the display unit 40. The display unit 40 is a display device such as a CRT (cathoderay tube) like the part shown in FIG. 10, and it is advantageous to include a circuit for printing the displayed measured waveform by hard copy or the like.

Next, the operation of the optical pulse tester according to the present embodiment will be described with reference to FIGS. in this case,
A description will be given while comparing the processing result according to the present embodiment with the processing result of the conventional optical pulse tester shown in FIG. First, the steps from the light pulse generation to the averaging processing are executed in the same manner as in the case of FIG. That is, the timing generation circuit 1
When the number of measurements, that is, the number of generations of light pulses, is set to a predetermined number in 02 and started, the timing signal is sequentially supplied from the timing generation circuit 102 to the drive circuit 104 at predetermined intervals. Accordingly, the drive circuit 104 supplies a drive signal to the light source 106 in response to the timing signal, and causes the light source 106 to sequentially generate light pulses of a predetermined wavelength.

A light pulse having a predetermined wavelength from the light source 106 is incident from one end of the optical fiber 1 through the directional coupler 202, and a part thereof is backscattered due to uneven distribution of the refractive index of the core. Then, the light returns to the incident end after being reflected by a connection portion or a deteriorated portion. The light that has returned to the incident end passes through the directional coupler 202 and is
And converted into an electric signal corresponding to the intensity of the detected light. The resulting signal is amplified by the amplifier 206 and supplied to the averaging circuit 302. The averaging circuit 302 samples the detection signal from the amplifier 206 in response to the timing signal from the timing generator 102, and forms a measurement waveform of a loss characteristic according to the distance of the optical fiber from the result.

The above steps, that is, the measurement from the input of the light pulse to the detection of the return light thereof are repeated a set number of times.
Each of the detection results is sampled and averaged by the averaging processing circuit 302, and the processing result is supplied to the logarithmic conversion circuit 304. In this case, for example, is the number of measurements 2 ⁹ times, as shown in FIG. 5, has a measured waveform near the distal end portion is buried in noise. The OTDR shown in FIG. 10, two more ^three times the number of measurements has been added, such measurements of 2 ¹² times repeated. In the present embodiment, it may be a number of measurements 2 ⁹ times, for comparison with the case shown in FIG. 10, the number of measurements 2 ¹² times will be described when it is set. Thereby, the logarithmic conversion circuit 30
The output of 4 is a measured waveform as shown in FIG. 6, for example. In this figure, the S / N ratio is slightly improved compared to the case shown in FIG. 5, but its waveform is not yet clear near its far end. In the optical pulse tester shown in FIG. 10, the number of measurements is further added and the above steps are repeated again.

In the present embodiment, when the measured waveforms shown in FIG. 6 are sequentially supplied from the logarithmic conversion circuit 304 to the SN range comparison circuit 304, the SN range comparison circuit 306 outputs the respective signal levels as shown in FIG. S set in advance
In comparison with the N ratio, each is divided into a region A to a region G in the figure, and the result is supplied to a moving average circuit 308. Thus, the moving average circuit 308 performs a moving average process on each point in each area, and supplies the processing result to the storage circuit 310.

More specifically, the process of the divided moving average process will be described with reference to FIG. 2. First, in step S10, logarithmically converted waveform data is sequentially supplied from the logarithmic conversion circuit 304 to the SN range comparison circuit 306. You. Then
The SN range comparison circuit 306 determines in step S12
It is determined whether or not the data is equal to or greater than the set value A, that is, whether or not the value is equal to or greater than 20 dB. If the value is equal to or larger than the set value A, the data is stored in the storage circuit 310 via the moving average circuit 308 in step S40. Thereby, for example, each data of area A shown in FIG. Next, since the data in the area B is smaller than the set value A, the process proceeds to step S14, and it is determined whether or not the value is equal to or larger than the set value B, that is, equal to or larger than 19.25 dB. As a result, if the value is equal to or greater than the set value B, the process proceeds to step S16, and the moving average circuit 308 adds and averages two data of the previous value and the value of the own point for each point to obtain the value of the own point. The averaging operation is performed, and the operation result proceeds to step S40 via step S36, and is stored in storage circuit 310.

Next, in step S18, each data in the area C is determined and supplied to the moving average circuit 308. In step S20, the number of data used for the moving average is increased from that in step S16. 2 ² that moving average calculation by the data and the total of four data using three data earlier in question is executed. The result proceeds to step S40 via step S36, and is stored in the storage circuit 310 as described above. Similarly, in step S22, the data in the area D is determined, and the process proceeds to step S24 for each data.
Moving average calculation using 2 ^three data is performed in. Step S26 or the data of the respective At step S30 area E or area F is determined respectively, moving average calculation using the 2 ^four data for each point in the region E in step S28 is executed, step S32
Moving average calculation using the 2 ^five data is performed for each point of the region F. Finally, for the data determined as the area G smaller than the set value F in step S30, a moving average calculation using ²⁶ data is executed in step S34. The result of each moving average proceeds to step S40 via step S36, and the storage circuit 310
Is stored.

When all the data is stored in step S40, the process proceeds to step S42, where the respective stored areas are combined, and the measured waveform from which the noise component has been removed is converted to the measured waveform in step S44, as shown in FIG. It is displayed on the display unit 40.

As described above, according to the optical pulse tester of the present embodiment, since the measured waveform subjected to the averaging process is further subjected to the divided moving average process, the SN ratio is improved and displayed.
Even when the S / N ratio was poor to some extent, the displayed waveform was clear. 7 shows the measurement waveform measurements were repeated 2 ¹⁸ times indicated by the OTDR shown in FIG. 10. FIG. 8 shows a measured waveform obtained by adding and averaging 2 ¹² times by the optical pulse tester of the present embodiment and further performing a division moving average process. As is clear from these figures, the measurement waveform processed by the optical pulse tester of the present embodiment is:
From the measured waveform of the measurements were repeated 2 ¹⁸ times by an optical pulse tester shown in FIG. 10, less the noise component, in particular, the waveform in the vicinity of its distal end portion is assumed clear. Thereby, in the present embodiment, it is possible to reduce the number of measurements of ²⁶ or more times as compared with the optical pulse tester shown in FIG.
The measurement time was able to 1/2 ^6.

In the above embodiment, the case where the result of repeating the predetermined number of measurements is averaged by the averaging circuit and the result is subjected to the divided moving average processing has been described as an example. Alternatively, the result obtained by changing the gain according to the SN ratio may be added and averaged by the averaging circuit 302, and the result may be subjected to the divided moving average processing. For example, FIG.
1 shows an embodiment of an optical pulse tester in which a gain adjustment circuit 60 is further added to that shown in FIG. In this embodiment, the number of measurements is further reduced than in the above-described embodiment, and a portion having a predetermined SN ratio or less is detected by the gain adjustment circuit 60 from the logarithmically converted waveform of the result of the averaging, and the gain of that portion is reduced. Increase and further measure. The results may be divided and averaged to remove noise components, synthesized, and displayed in the same manner as in the above embodiment.

[0029]

As described above, according to the optical pulse tester of the present invention, the optical pulse from the optical pulse generating means is incident on the optical fiber, and the return light is detected by the return light detecting means, and the electric power is detected. When the measurement signal is converted into a signal and the measurement signal representing the loss characteristic according to the distance of the optical fiber is formed by the waveform processing means based on the detection signal, the detection signal from the return light detection means is predetermined by the averaging processing means. At the timing of the above, to form a measured waveform that is added and averaged according to the number of repetitions of the light pulse in the light pulse generating means, and further based on the measured waveform based on the SN ratio preset in the divided moving average means. And the moving average processing is applied to each point along each waveform for each area. Is displayed is effectively improved Te. As a result, even if the result of the addition and averaging has a poor SN ratio to some extent, the displayed waveform becomes clear. Therefore, a highly accurate measurement waveform can be obtained from the measurement result as compared with the processing of only the averaging, and the number of times of the measurement can be reduced. As a result, the measurement time can be effectively reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical pulse tester according to the present invention.

FIG. 2 is a flowchart illustrating an operation of a main part of the optical pulse tester according to the embodiment of FIG. 1;

FIG. 3 is a waveform chart showing a measured waveform before a divided moving average in the optical pulse tester according to the embodiment of FIG. 1;

FIG. 4 is a waveform chart showing a display waveform in the optical pulse tester according to the embodiment of FIG. 1;

5 is a waveform diagram showing a measurement waveform before divided moving averaging in the optical pulse tester according to the embodiment of FIG. 1 or a display waveform in the optical pulse tester of FIG. 10;

6 is a waveform diagram showing a measurement waveform before divided moving average in the optical pulse tester according to the embodiment of FIG. 1 or a display waveform in the optical pulse tester of FIG. 10;

FIG. 7 is a waveform diagram showing a display waveform in the optical pulse tester of FIG.

FIG. 8 is a waveform diagram showing a display waveform in the optical pulse tester according to the embodiment of FIG. 1, and is a diagram for comparison with the display waveform of FIG. 7;

FIG. 9 is a block diagram showing another embodiment of the optical pulse tester according to the present invention.

FIG. 10 is a block diagram showing a conventional optical pulse tester.

[Explanation of symbols]

 Reference Signs List 10 optical pulse generation unit 20 return light detection unit 30 waveform processing unit 40 display unit 50 divided moving average processing unit 60 gain adjustment circuit 302 averaging processing circuit 304 logarithmic conversion circuit 306 SN range comparison circuit 308 moving average circuit 310 storage circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Katsumi Hirata, Inventor Katsumi Hirata 4-19-7 Kamata, Ota-ku, Tokyo Ando Electric Co., Ltd. F-term (reference) 2G086 CC03 KK01 5K002 BA05 EA06 FA01 5K042 CA10 DA17 EA03 FA15 FA25 GA12 HA01

Claims (3)

[Claims] An optical pulse tester for injecting a predetermined optical pulse from one end into an optical fiber under test (1) and measuring the signal level of the return light to test the loss characteristic of the optical fiber. An optical pulse generating means (10) for generating a predetermined optical pulse by repeating a predetermined number of times at a desired interval; and an optical pulse from the optical pulse generating means being incident on an optical fiber and detecting a return light thereof. Return light detecting means (20) for converting the optical signal into an electric signal, and a waveform processing means (30) for forming a measurement waveform representing a loss characteristic corresponding to the distance of the optical fiber based on the detection signal from the return light detecting means. Display means (40) for displaying a measurement waveform formed by the waveform processing means, wherein the waveform processing means samples a detection signal from the return light detection means at a predetermined timing, and Averaging means for forming a measured waveform obtained by averaging according to the number of repetitions of light pulses at, respectively the light pulse generating means (3
02) and dividing the measured waveform formed by the averaging means into a plurality of regions based on a preset S / N ratio, and for each region, a plurality of data along the waveform at each point of the waveform. An optical pulse tester, comprising: a divided moving average means (50) for performing a moving average process using the moving average processing. 2. An optical pulse tester according to claim 1, wherein said waveform processing means performs logarithmic conversion on each value of a processing result from said averaging processing means.
04), wherein the divided moving average means compares the logarithm-converted result by the logarithmic conversion means to determine whether each value is within a preset SN ratio range, and divides the area into divided area setting means. (306) and S for each point of the area divided by the division range setting means.
Moving average calculation means (308) for calculating by increasing the number of data used for the moving average as the N ratio is lowered,
A storage means (310) for synthesizing and storing results processed for each area by said moving average calculation means. 3. The optical pulse tester according to claim 1, wherein the tester detects the number of times of averaging or return light based on a processing result of the measurement waveform formed by the averaging processing means. Gain adjusting means (6) for adjusting the gain
0), wherein the divided moving average means further performs divided moving average processing on the measurement waveform from the averaging processing means after being adjusted by the gain adjusting means.