JP2008116378A - Light pulse tester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light pulse tester capable of carrying out measurement precisely in a short time. <P>SOLUTION: The present invention relates to an improved light pulse tester for emitting a plurality of times a pulsed light to an optical fiber to be measured, at the first measuring period, and for measuring the optical fiber to be measured by detecting a return light of the pulsed light by a photoreception part. The tester includes an observed data storage part for storing a data of the return light from the photoreception part, a reference data storage part for stopping the emission of pulse light, and for storing the data from the photoreception part at the second measuring period shorter than the first measuring period, a reference value computing means for finding a reference value based on the data of the reference data storage part, and a correction means for correcting the data of the observed data storage part by the reference value found by the reference value computing means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pulse tester that emits pulsed light to a measured optical fiber a plurality of times at a first measurement period, and a light receiving unit detects the return light of the pulsed light to measure the measured optical fiber. Specifically, the present invention relates to an optical pulse tester capable of performing measurement with high accuracy in a short time.

  In an optical communication system that performs data communication using an optical signal, it is important to monitor an optical fiber that transmits the optical signal. An optical pulse tester (hereinafter abbreviated as OTDR (Optical Time Domain Reflectometer)) is used for laying and maintaining optical fibers. In OTDR, pulse light is repeatedly incident on the optical fiber under measurement from the measurement connector at the input / output end of the OTDR, and the levels of the reflected light and backscattered light from the optical fiber to be measured and the light reception time are measured. Measure the state of the measurement optical fiber such as breakage and loss.

  FIG. 3 is a diagram showing a configuration of a conventional OTDR (see, for example, Patent Document 1). In FIG. 3, an optical fiber to be measured F1 is an optical fiber to be measured on which measurement of disconnection, loss, and the like is performed. The OTDR 100 has a measurement connector CN connected to the optical fiber F1 to be measured, and outputs pulsed light from the measurement connector CN to the optical fiber F1 to be measured, and return light (reflected light or backscattered light) of this pulsed light. Is input via the measurement connector CN.

  The OTDR 100 includes a light emitting unit 10, an optical coupler 20, a band pass filter (hereinafter abbreviated as BPF) 30, a light receiving unit 40, a storage unit 50, a signal processing unit 60, and a display unit 70. The light emitting unit 10 outputs pulsed light. The optical coupler 20 outputs the pulsed light from the light emitting unit 10 to the bandpass filter 30 and outputs the return light from the measured optical fiber F1 to the light receiving unit 40. The BPF 30 is provided between the optical coupler 20 and the measurement connector CN, and transmits only light in a predetermined wavelength band (including the wavelength of the pulsed light of the light emitting unit 10). The light receiving unit 40 receives light from the optical coupler 20. The storage unit 50 stores data from the light receiving unit.

  The signal processing unit 60 includes a reference value (hereinafter abbreviated as REF value) calculation unit 61, a correction unit 62, and a return light calculation unit 63, controls the output timing of the pulsed light of the light emitting unit 10, and the storage unit 50. Read the data. The REF value calculation means 61 obtains a REF value from the data in the storage unit 50. The correction unit 62 corrects the data in the storage unit 50 with the REF value of the REF value calculation unit 61. The return light calculation means 63 receives the correction data of the correction means 62. The display unit 70 displays the processing result of the signal processing unit 60.

  The operation of such an apparatus will be described. Here, FIG. 4 is a diagram showing an example of the measurement result of the return optical signal. The horizontal axis represents the distance from the measurement connector CN (the time series data from the light receiving unit 40 converted into the distance), and the vertical axis represents the optical power of the return light.

  The light emitting unit 10 outputs pulsed light at a predetermined timing in accordance with an instruction from the signal processing unit 60. Then, the pulsed light output from the light emitting unit 10 enters the measured optical fiber F1 through the optical coupler 20, the BPF 30, and the measurement connector CN. Rayleigh scattering occurs inside the optical fiber F1 to be measured, and a part thereof travels in the direction opposite to the traveling direction of the pulsed light and returns to the OTDR 100 as backscattered light. Further, the Fresnel reflected light generated at the connection point of the measured optical fiber F1 also returns to the OTDR 100.

  Then, the return light from the measured optical fiber F1 enters the light receiving unit 40 through the measurement connectors CN, BPF 30, and the optical coupler 20. Further, an OE conversion circuit (not shown) of the light receiving unit 40 converts the incident light into an electric signal (photocurrent) corresponding to the optical power of the incident light. Then, the IV conversion circuit (not shown) of the light receiving unit 40 converts the photocurrent into a voltage, and the amplification circuit (not shown) of the light receiving unit 40 amplifies the converted voltage to a desired level.

  Further, an AD conversion circuit (not shown) of the light receiving unit 40 AD-converts an analog signal into a digital signal and stores the data in the storage unit 50 in chronological order. Here, the data from the light receiving unit 40 is referred to as actually measured data. Since the signal level of the return light is very weak, in order to expand the dynamic range, pulse light is repeatedly output (for example, 2 ^ 8 to 2 ^ 18 times) to the measured optical fiber F1 and measured data for a plurality of times. Is stored in the storage unit 50.

  Further, the actual measurement data is acquired for a longer distance (A0 in FIG. 4) than the portion (A1 in FIG. 4) displayed on the display screen of the display unit 60. In addition, the range of A0 in FIG. 4 becomes a measurement period.

  As shown in the measurement waveform example shown in FIG. 4, the optical fiber to be measured F1 has a loss from the near end (left end of the horizontal axis in FIG. 4) on the measurement connector CN side of the OTDR 100 toward the far end. The waveform is shown. Further, the noise floor level of each circuit in the light receiving unit 40 of the OTDR 100 is displayed after the far end of the measured optical fiber F1.

  Then, the REF value calculation means 61 of the signal processing unit 60 reads out a plurality of actually measured data (portion A0 in FIG. 2) from the storage unit 50, adds the measured data at the same distance position, and averages them. Further, when the REF value calculation means 61 has the signal level of the return light from the measured optical fiber F1 in the actual measurement data (averaged at the same distance position) sufficiently buried in the noise generated in the light receiving unit 40. A REF value as a reference value is obtained from the data of a possible part (A3 in FIG. 4). The data for obtaining the REF value is referred to as reference data (hereinafter referred to as REF data). The median value or average value of the REF data becomes the REF value. Then, the obtained REF value is output to the correction means 62.

  Then, the correction unit 62 reads the actual measurement data from the storage unit 50, subtracts the read actual measurement data by the REF value, and outputs it to the return light calculation unit 63. When the subtraction of all the actual measurement data by the correction unit 62 is completed, the return light calculation unit 63 averages the corrected (subtracted) actual measurement data at the same distance position, and displays the A1 portion of the averaged actual measurement data on the display unit 70. To display.

JP-A-11-344416

  The REF value calculation means 61 obtains the REF value, and the correction means 62 corrects the actually measured data with the REF value, whereby the linearity can be improved.

  When obtaining this REF value, if the acquisition position A3 of the REF data is too close to the position (time zone) where the return optical signal from the measured optical fiber F1 returns, the influence of the return optical signal is completely removed. I can't. For this reason, the REF value is increased as compared with a true REF value that is not affected by the return optical signal. When the actual measurement data is corrected using such a REF value, there is an excessive correction, and on the contrary, linearity deterioration (so-called waveform suction phenomenon) occurs, and there is a problem that measurement accuracy deteriorates.

  On the other hand, in order to minimize the influence of the return optical signal, the REF data acquisition portion A3 is made sufficiently longer than the light emission timing of the LD (not shown) of the light emitting unit 10 (the return optical signal from the optical fiber F1 to be measured is It should be taken long enough from the time of return). In FIG. 4, the data of the portion A2 that is not used for the screen display and the REF data may be long.

  However, if the A2 portion is lengthened in order to minimize the influence of the return optical signal, one measurement cycle is lengthened. Even if the portion A2 is small with respect to the screen display portion A1 and the time loss per measurement cycle is small, the OTDR 100 measures about 2 ^ 8 to 2 ^ 18 times as described above, and averages these values. Is the final measurement result. That is, there is a problem that even if the time loss for each time is small, the total measurement time for obtaining the final measurement result is very large.

  Therefore, an object of the present invention is to realize an optical pulse tester capable of performing measurement with high accuracy in a short time.

The invention described in claim 1
In an optical pulse tester that emits pulsed light to a measured optical fiber a plurality of times at a first measurement period, and a light receiving unit detects return light of the pulsed light to measure the measured optical fiber,
An actual measurement data storage unit for storing data of return light from the light receiving unit;
A reference data storage unit for stopping emission of pulsed light and storing data from the light receiving unit in a second measurement cycle shorter than the first measurement cycle;
A reference value calculation means for obtaining a reference value from the data in the reference data storage unit;
A correction means for correcting the data in the actual measurement data storage section with the reference value obtained by the reference value calculation means is provided.
The invention according to claim 2 is the invention according to claim 1,
A display unit for displaying a measurement result of the optical fiber to be measured;
The first measurement period is a time corresponding to data displayed on the display unit.

  According to the present invention, by stopping the emission of the pulsed light, the reference value calculation means obtains the reference value using only the noise data generated in the light receiving unit. Then, the correction means corrects the return light data with the reference value. Thereby, it is possible to suppress the acquisition of useless data as compared with the case of extracting the reference data from the return light data. Therefore, the total measurement time for obtaining the final measurement result can be shortened, and the measurement can be performed with high accuracy in a short time.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. Here, the same components as those in FIG. In FIG. 1, a storage unit 80 is provided instead of the storage unit 50, and a signal processing unit 90 is provided instead of the signal processing unit 60.

  The storage unit 80 includes a REF data storage unit 81 that stores REF data, a REF value storage unit 82 that stores REF values, and an actual measurement data storage unit 83 that stores actual measurement data.

  The signal processing unit 90 includes a REF value calculation unit 91, a correction unit 92, and a return light calculation unit 93, controls the output timing of the pulsed light from the light emitting unit 10, and reads data in the storage unit 80.

  The REF value calculation unit 91 reads the REF data in the REF data storage unit 81 to obtain the REF value, and stores the obtained REF value in the REF value storage unit 82. The correction unit 92 corrects the data of the actual measurement data 83 with the REF value of the REF value storage unit 82. The return light calculation means 93 receives the actual measurement data corrected by the correction means 93. The display unit 70 displays the processing result of the signal processing unit 90.

  The operation of such an apparatus will be described. Here, FIG. 2 is a diagram illustrating an example of the measurement result. The horizontal axis represents the distance from the measurement connector CN (the time series data from the light receiving unit 40 converted into the distance), and the vertical axis represents the optical power. FIG. 2A shows the measurement result of the return light signal, and FIG. 2B shows the measurement result in a state where no pulsed light is emitted.

  In the apparatus shown in FIG. 1, pulsed light is emitted to the optical fiber F1 to be measured, and the return light is measured. Thereafter, the emission of the pulsed light is stopped and the operation for obtaining the REF value is performed. Furthermore, the measurement optical fiber F is measured by correcting the actual measurement data of the return light with the REF value.

  First, the operation of emitting pulsed light to the measured optical fiber F1 and measuring the return light will be described. The light emitting unit 10 outputs pulsed light at a predetermined timing in accordance with an instruction from the signal processing unit 90. Then, the pulsed light output from the light emitting unit 10 enters the measured optical fiber F1 through the optical coupler 20, the BPF 30, and the measurement connector CN. Rayleigh scattering occurs inside the optical fiber F1 to be measured, and a part thereof travels in the direction opposite to the traveling direction of the pulsed light and returns to the OTDR 100 as backscattered light. Further, the Fresnel reflected light generated at the connection point of the measured optical fiber F1 also returns to the OTDR 100.

  Then, the return light from the measured optical fiber F1 enters the light receiving unit 40 through the measurement connectors CN, BPF 30, and the optical coupler 20. Further, an OE conversion circuit (not shown) of the light receiving unit 40 converts the incident light into an electric signal (photocurrent) corresponding to the optical power of the incident light. Then, the IV conversion circuit (not shown) of the light receiving unit 40 converts the photocurrent into a voltage, and the amplification circuit (not shown) of the light receiving unit 40 amplifies the converted voltage to a desired level.

  Further, an AD conversion circuit (not shown) of the light receiving unit 40 AD-converts the analog signal into a digital signal, and stores the data in the measured data storage unit 83 of the storage unit 80 in time series. Since the signal level of the return light is very weak, in order to expand the dynamic range, pulse light is repeatedly output (for example, 2 ^ 8 to 2 ^ 18 times) to the measured optical fiber F1 and measured data for a plurality of times. Is stored in the storage unit 83.

  Further, since only the actual measurement data of the screen display part is measured, there is no need to acquire the part A2 and the REF data acquisition part A3 as in the apparatus shown in FIG. Therefore, as shown in FIG. 2A, the screen display portion is approximately equal to one measurement cycle (first measurement cycle).

Next, the emission of the pulsed light is stopped and the operation for obtaining the REF value is performed.
When the measurement of the measurement data for a predetermined number of times is completed, the signal processing unit 90 causes the light emitting unit 10 to stop emitting pulsed light. The light receiving unit 40 stores the actual measurement data of only noise generated in the light receiving unit 40 in the REF data storage unit 81 as REF data. Since no pulsed light is emitted from the light emitting unit 10, as shown in FIG. 2 (b), the REF data acquisition portion is approximately equal to one measurement cycle (second measurement cycle).

  When the REF data for a predetermined number of times is stored in the REF data storage unit 81, the REF value calculation means 91 reads the REF data from the REF data storage unit 81, adds the REF data at the same distance position, and averages them. Further, a median value or average value of all averaged REF data is obtained, and the obtained median value or average value is stored in the REF value storage unit 82 as a REF value. Thus, the REF value corresponds to the noise floor level of the light receiving unit 40.

Next, an operation of measuring the measured optical fiber F by correcting the actual measurement data of the return light with the REF value is performed.
The correction unit 92 reads the REF value from the REF value storage unit 82. Then, the correction unit 92 sequentially reads the actual measurement data from the actual measurement data storage unit 83, subtracts each by the REF value, corrects it, and outputs the corrected actual measurement data (hereinafter, correction data) to the return light calculation unit 93. . Then, the return light calculation means 93 adds the correction data at the same distance position and averages them. Further, the return light calculation means 93 measures the distance of the measured optical fiber F1 and the optical signal level of the return light from the timing when the pulse light is output and the time when the return light is received by the light receiving unit 40, and the measurement result. Is displayed on the display unit 70 with the horizontal axis representing the distance and the vertical axis representing the optical power (optical signal level) of the return light.

  In this way, the emission of the pulsed light is stopped, and the REF value calculation unit 91 obtains the REF value using the actual measurement data of only the noise generated in the light receiving unit 40. Then, the correction means 92 corrects the actual measurement data of the return light with the REF value, so that (actual measurement data measurement time of the return light) ≈ (screen display portion) ≈ (first measurement cycle), and (REF data measurement) Time) ≈ (second measurement cycle). That is, it is not necessary to acquire useless actual measurement data (A2 portion in FIG. 4) unlike the apparatus shown in FIG. In general, the number of measurement points of actual measurement data is about 2000 points depending on the distance resolution, but about 100 to 1000 points are sufficient for the REF data because only noise generated in the light receiving unit 40 is obtained. That is, (first measurement period of REF data) <(second measurement period of the return optical signal). Thereby, the total measurement time for obtaining the final measurement result can be shortened. Therefore, it is possible to measure accurately in a short time.

  Further, since it is sufficient for the REF data to obtain noise generated in the light receiving unit 40, the number of times of measurement of the REF data can be made smaller than the number of times of measurement of the actual measurement data of the return light. Thereby, the total measurement time can be shortened.

  Further, since the measurement of the return light and the measurement of the REF data are separated, it is possible to leave a predetermined time before the measurement of the REF data. As a result, REF data can be measured without any influence of the return light of the pulsed light, and a sufficiently accurate REF value can be calculated even if the number of REF data measurement points and the number of measurements are further reduced. Can do. Accordingly, the amount of calculation is reduced and the total measurement time can be shortened.

  In addition, when measurement is performed with the same total measurement time as in the conventional case, the number of returned light measurements can be increased, and the number of averaging processing additions can be increased. Thereby, the dynamic range of measurement can be improved.

The present invention is not limited to this, and may be as shown below.
Although the configuration in which the measurement of the REF data and the calculation of the REF value is performed after the return light is measured is shown, the REF value may be calculated first and then the return light may be measured.

  Further, when the measurement optical fiber F is repeatedly measured under the same measurement conditions (measurement conditions such as measurement period, optical power of pulsed light, and measurement distance range), the REF value is not obtained for each final measurement result. The measured data may be corrected using the same REF value. Thereby, the time for obtaining the REF value can be omitted, so that the measurement time can be further shortened.

  Also, when the number of times of averaging is large and the measurement time of the return light becomes very long, for example, when measuring 2 ^ 18 times, REF data is acquired when 2 ^ 9 measurements are completed, and 2 ^ REF data may be acquired again after 18 measurements. Thereby, the influence by the change of the measurement environment (for example, temperature) during long-time measurement can be suppressed.

  And the correction means 92 showed the structure which correct | amends each actual measurement data by REF value, and averages between the actual measurement data of the same distance position after that, Averaged between the actual measurement data of the same distance value, and averaged The actual measurement data may be corrected with the REF value.

It is the block diagram which showed one Example of this invention. It is the figure which showed an example of the measurement result of the apparatus shown in FIG. It is the figure which showed the structure which connected the to-be-measured optical fiber to the conventional OTDR. It is the figure which showed an example of the measurement result of the apparatus shown in FIG.

Explanation of symbols

40 Light Receiving Unit 70 Display Unit 81 REF Data Storage Unit 83 Actual Measurement Data Storage Unit 91 REF Value Calculation Unit 92 Correction Unit F1 Optical Fiber to be Measured

Claims (2)

In an optical pulse tester that emits pulsed light to a measured optical fiber a plurality of times at a first measurement period, and a light receiving unit detects return light of the pulsed light to measure the measured optical fiber,
An actual measurement data storage unit for storing data of return light from the light receiving unit;
A reference data storage unit for stopping emission of pulsed light and storing data from the light receiving unit in a second measurement cycle shorter than the first measurement cycle;
A reference value calculation means for obtaining a reference value from the data in the reference data storage unit;
An optical pulse tester provided with a correction means for correcting the data in the actual measurement data storage section with the reference value obtained by the reference value calculation means. A display unit for displaying a measurement result of the optical fiber to be measured;
The optical pulse tester according to claim 1, wherein the first measurement period is a time corresponding to data displayed on the display unit.

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