JP3002340B2 - Optical pulse tester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying an optical pulse to an optical fiber to be measured and detecting and detecting backscattered light and Fresnel reflected light which are scattered and returned in the optical fiber to be measured. The present invention relates to an optical pulse tester that measures the optical loss and the position of a fault point of an optical fiber to be measured by performing signal processing.

[0002]

2. Description of the Related Art An optical pulse is supplied to an optical fiber to be measured.
By receiving and detecting the reflected light returning from the optical fiber to be measured with the supply of this light pulse and processing the signal,
2. Description of the Related Art An optical pulse tester is known as a device for measuring the optical loss of a measured optical fiber, the position of an injury point, and the like.

FIG. 7 is a block diagram showing an example of the configuration of this type of optical pulse tester. The optical pulse tester includes a timing generator 21, a light emitting element driving unit 22, an E / O converter 23, a coupler 24, an O / E converter 25, and a signal processing unit 2.
6. The display 27 is provided. In this optical pulse tester, when the timing generator 21 generates a synchronization signal at a predetermined repetition cycle, and the light emitting element driving unit 22 outputs a current pulse to the E / O converter 23 at the input timing of the synchronization signal, The / O converter 23 supplies an optical pulse to the measured optical fiber 28 via the coupler 24. When the optical pulse is supplied to the measured optical fiber 28, Fresnel reflection (reflected light) and backscattered light (scattered light) are generated in the measured optical fiber 28. The Fresnel reflected light and the backscattered light are received and detected by the O / E converter 25 via the coupler 24 and are converted into electric signals. After the converted signal is amplified to a predetermined level and converted into a digital signal, the signal processing unit 26 performs signal processing of integrated averaging and logarithmic conversion, and the result is displayed in a waveform on a display 27.

Since the backscattered light from the measured optical fiber 28 is a very weak signal, the above-described conventional optical pulse tester periodically supplies an optical pulse to the measured optical fiber 28, The S / N ratio is improved by integrating and averaging the backscattered light. In this case, the repetition period of the emission of the optical pulse needs to be longer than the time for the optical pulse to reciprocate through the optical fiber 28 to be measured. Was.

[0005]

However, if the repetition period is made unnecessarily long, the number of additions of the integrated average performed by the signal processing unit 26 within the same time is reduced, and the S / N
There was a problem that the improvement of the ratio became worse. On the other hand, if the repetition period is too short, the reflected light of the measured optical fiber 28 and the reflected light of the measured optical fiber 28 that return with the supply of the next light pulse are overlapped and the waveform is distorted. Measurement could not be performed.

Further, a far end 28a of the optical fiber 28 to be measured is
3A, the returned Fresnel reflected light is reflected again inside the connector at the near end 28b or inside the optical pulse tester, and the length L of the measured optical fiber 28 is reduced, as shown in FIG. Secondary Fresnel reflected light may appear at twice the distance.

Therefore, in the conventional optical pulse tester, FIG.
As shown in (1), the measurer has selected the optimum distance range from a plurality of distance ranges set in advance from the length L of the measured optical fiber 28 in consideration of the influence of the secondary reflection described above. In the optical pulse tester, the round trip time of light is calculated from the distance range, and a time corresponding to twice the distance is set as a repetition period.

For this reason, in the conventional optical pulse tester, the repetition period of the measurement range is twice the length of the measured optical fiber 28 regardless of the presence or absence of the secondary reflected light from the far end 28a of the measured optical fiber 28. Since it is fixedly set to the time required to reciprocate in L, there is a problem that the optimum repetition cycle is not set when the secondary reflection of the far end 28a of the optical fiber under measurement 28 does not occur. In addition, there is also an operational inconvenience that the measurer must set an optimum distance range each time from the length L of the measured optical fiber 28.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to automatically calculate and optimally set a repetition period of an optical pulse supplied to an optical fiber to be measured. It is an object of the present invention to provide an optical pulse tester capable of performing the following.

[0010]

In order to achieve the above object, an optical pulse tester according to the first aspect of the present invention is set in advance to a time longer than a time corresponding to a distance in which an observation waveform can be detected. Data sampling means 7a for sampling a waveform signal when an optical pulse is supplied to the optical fiber 9 to be measured based on a synchronization signal having a repetition period T.
And a plurality of waveform data sampled by the data sampling means, a data comparison means 7c for comparing a predetermined noise level Ln indicating a detection limit of the waveform signal, and a data comparison means based on a result of the data comparison means. A sampling position calculator 7d for calculating a sampling position of waveform data farthest from the near end 9b of the optical fiber to be measured exceeding the noise level; and an optical pulse emitted from the optical fiber to be measured by emitting an optical pulse to the optical fiber to be measured. A repetition period correction unit 7e for correcting the initially set repetition period, using a value larger and close to the reciprocating time t to the sampling position calculated by the sampling position calculation unit as a correction repetition period TA. Features.

[0011]

In the optical pulse tester according to the present invention, the measurement point EA of the optical fiber under test is set as the reference point P0 with the emission point of the optical pulse supplied to the optical fiber under test 9 based on the timing of the synchronization signal. And range setting means 11 for setting two different repetition periods T1 and T2 of the synchronization signal for a time longer than at least the time including the measurement range from the reference point. Sampling means 12a and 12b for sampling waveform signals from the optical fiber to be measured at two different repetition periods set by the means, and data comparison for comparing two sets of waveform data by the sampling means within the measurement range. When the two sets of waveform data by the means 12c and the data comparing means do not match, the shorter repetition cycle is set to the other repetition rate. Range switching means 12d for switching to a range longer than the return cycle, and repetition cycle determination means 12e for setting the shorter repetition cycle as the optimum repetition cycle when two sets of waveform data by the data comparison means match. It is characterized by having.

Further, in the optical pulse tester according to the present invention, the measuring point EA of the optical fiber to be measured is defined as the reference point P0 with the emission point of the optical pulse supplied to the optical fiber to be measured 9 based on the timing of the synchronization signal. A range setting unit 10 for setting two different repetition periods T1 and T2 of the synchronization signal in a time longer than at least the time including the measurement range from the reference point.
Sampling means 12a and 12b for sampling waveform signals from the optical fiber under measurement at two different repetition periods set by the range setting means, and comparing two sets of waveform data by the sampling means within the measurement range. A data comparing means 12c, a range switching means 12d for switching a longer repetition cycle to a shorter time range than the other repetition cycle when two sets of waveform data coincide with each other, and the data comparing means. A repetition cycle determining means for setting a longer repetition cycle as an optimum repetition cycle when two sets of waveform data do not match each other.

[0014]

In the optical pulse tester according to the first aspect, the optical fiber 9 to be measured is transmitted to the optical fiber 9 to be measured based on a synchronization signal having a repetition period T previously set to a time longer than a time corresponding to a distance in which an observation waveform can be detected. When the pulse is supplied, the backscattered light and the Fresnel reflected light return from the measured optical fiber 9 with the supply of the light pulse. Waveform signals due to these reflected lights are sampled into waveform data by the data sampling means 7a. Each waveform data is compared by the data comparison means 7c with a preset noise level Ln indicating the detection limit of the waveform signal. Based on the comparison result, the sampling position calculation means 7d calculates the sampling position of the waveform data farthest from the position of the near end 9b of the measured optical fiber 9 exceeding the noise level Ln.
The repetition period correcting means 7e emits an optical pulse to the measured optical fiber 9, and determines a value larger and close to the reciprocating time t to the sampling position calculated by the sampling position calculating means 7d of the measured optical fiber 9 as the correction repetition period TA. To correct the initially set repetition period T.

[0015]

In the optical pulse tester according to the second aspect, the measuring range setting means sets the emission point of the optical pulse supplied to the optical fiber to be measured as a reference point P0.
The measurement range EA is set. The range setting means 11 sets at least two repetition periods T1 and T2 of different synchronization signals for a time longer than the time including the measurement range EA from the reference point P0.
Set. With this setting, when the optical pulses with the two sets of repetition periods T1 and T2 are sequentially supplied to the optical fiber 9 to be measured, the sampling means 12a and 12b cause the sampling means 12a and 12b to output the optical pulses from the optical fiber 9 to be measured due to the supply of the optical pulses. The waveform signal is sampled every two different repetition periods T1 and T2. The data comparing means 12c compares two sets of waveform data obtained by sampling within the measurement range EA. When the two sets of waveform data match, the repetition cycle determination means 12e sets the shorter repetition cycle as the optimum repetition cycle. When the two sets of waveform data do not match, the range switching means 12d sets the shorter repetition cycle. To a range longer than the other repetition cycle,
Data comparison is performed until the sets of waveform data match.

In the optical pulse tester of the third aspect, in the data comparison, when two sets of waveform data do not match, the longer repetition cycle is set as an optimum repetition cycle, and the two sets of waveform data are used. When they match, the longer repetition cycle is switched to a shorter time range than the other repetition cycle, and data comparison is performed until the two sets of waveform data become inconsistent.

[0018]

FIG. 1 is a block diagram showing an embodiment of an optical pulse tester according to the present invention. The optical pulse tester according to this embodiment includes an initial range setting unit 1, a timing generation unit 2, a light emitting element driving unit 3, an E / O conversion unit 4, an optical branching and coupling unit 5, an O / E conversion unit 6, a signal processing unit. 7, and display means 8.

The initial range setting means 1 considers the influence of secondary reflection (multi-order reflection) from the far end 9a of the optical fiber 9 to be measured, and sets the repetition period T of the synchronization signal to the optical fiber 9 to be measured.
Is initially set to a time longer than the time corresponding to the detectable distance of the observed waveform.

The timing generating means 2 outputs a synchronizing signal of a repetition period T according to the range initially set by the initial range setting means 1 to the light emitting element driving means 3 and the signal processing means 7.

The light emitting element driving means 3 outputs a current pulse to the E / O conversion means 4 at, for example, the rising timing of the synchronizing signal inputted from the timing generating means 2.

The E / O conversion means 4 is, for example, an LD (Laser Diode).
ode), and outputs an optical pulse to the optical branching / coupling means 5 at, for example, the rising timing of the current pulse input from the light emitting element driving means 3.

The optical branching / coupling means 5 is composed of, for example, a fiber coupler, an optical branching coupler, an optical directional coupler, an optical switch, etc., and emits an optical pulse from the E / O conversion means 4 to the optical fiber 9 to be measured. ing.

The O / E conversion means 6 is, for example, an APD (Avalan
The backscattered light and the Fresnel reflected light returning from the optical fiber 9 to be measured with the supply of the light pulse are received and detected, converted into an electric signal, and output to the signal processing means 7.

The signal processing means 7 processes the reflected light from the measured optical fiber 9 at, for example, the rising timing of the synchronizing signal from the timing generation means 2. The signal processing means 7 a, the noise level calculating means 7 b, It comprises a comparing means 7c, a sampling position calculating means 7d, and a repetition period calculating means 7e.

The data sampling means 7a samples the electric signal from the O / E conversion means 6 at a predetermined sampling period, for example, at the rising timing of the synchronization signal input from the timing generation means 2, and is obtained by this sampling. A plurality (n) of waveform data are output to the data comparing means 7c. The data sampling means 7a averages m pieces of zero data in a section (zero sampling range) from the end of the synchronization signal having no reflected light from the measured optical fiber 9 to the rise of the next synchronization signal to obtain offset data. The logarithmic conversion is performed by subtracting the offset data from each waveform data. The logarithmically converted data is displayed as a waveform on the display unit 8 within a preset measurement range.

The noise level calculating means 7b calculates a noise level indicating the detection limit level of the waveform signal, and calculates a predetermined magnification by averaging the peak value of zero data or zero data sampled by the data sampling means 7a. Is calculated as the noise level.

The data comparing means 7c is connected to the optical fiber 9 to be measured.
, That is, the waveform data indicating the position of the far end 9a, that is, the last waveform data D (n) of the plurality of waveform data sampled by the data sampling means 7a, and sequentially comparing the level with the noise data of the noise level calculation means 7b. I have.

The sampling position calculating means 7d calculates the sampling position of the waveform data farthest from the position of the near end 9b of the measured optical fiber 9 exceeding the level of the noise data based on the comparison result of the data comparing means 7c.
Is calculated).

The repetition period corrector 7e emits an optical pulse to the measured optical fiber 9 for a time corresponding to the sampling position calculated by the sampling position calculator 7d, and reciprocates to the sampling position of the measured optical fiber 9. A time t is calculated, and a near value larger than the time t and considering the zero data sampling range is calculated as an optimum correction repetition cycle TA, and the repetition cycle T of the synchronization signal currently output by the timing generation means 2 is calculated as Correction is set to the calculated value TA.

Next, the operation of the optical pulse tester configured as described above when setting the correction of the repetition period of the synchronization signal will be described with reference to the flowchart of FIG. First, a range is set by the initial range setting means 1 in order to determine an initial synchronization signal repetition period T (ST1).
When the range is set, the timing generating means 2 generates a synchronization signal at a repetition period T of the set range,
Optical pulses are supplied from the O-conversion means 4 to the optical fiber 9 to be measured via the optical branching / coupling means 5 at the rising timing of the synchronization signal at every repetition period T (ST2).

Backscattered light and Fresnel reflected light return from the measured optical fiber 9 with the supply of the light pulse, and the reflected light is received and detected by the O / E conversion means 6 via the light branching / coupling means 5. Is converted to an electric signal (ST
3). This electrical signal is sampled by the data sampling means 7a at the timing of the rising edge of the synchronizing signal at the repetition period T, and as a result, a plurality (n) of waveform data is captured (ST4).

The plurality of sampled waveform data are compared by the data comparing means 7c with the noise data for all the sampled waveform data from the last waveform data to the first waveform data in order (ST5).

Based on the result of this comparison, the sampling position calculating means 7d determines that the measured optical fiber 9 exceeds the noise level.
The sampling position of the waveform data farthest from the position of the near end 9b is calculated (ST6). That is, as shown in the observation waveform of FIG. 3A, the secondary Fresnel reflection appears after the Fresnel reflection at the far end 9a of the measured optical fiber 9, and the level of the secondary Fresnel reflection exceeds the noise level Ln. Then, the position P1 of the secondary reflection is calculated as the sampling position of the waveform data farthest from the position of the near end 9b of the optical fiber 9 to be measured. 3B, if the secondary Fresnel reflection does not appear after the Fresnel reflection at the far end 9a of the optical fiber 9 to be measured, the position from the near end 9b of the optical fiber 9 to be measured is most likely. The position P2 of the far end 9a which exceeds the noise level Ln at a far position is calculated as a sampling position.

Subsequently, the repetition cycle calculating means 7e calculates a value which is longer than the time t corresponding to the sampling position and is close to the zero data sampling range in consideration as the optimum correction repetition cycle TA (ST7), and is currently set. The repetition cycle T is corrected and set to the calculated correction repetition cycle TA (ST8). As a result, the timing generator 2 generates a synchronization signal having a repetition period TA, and an optical pulse is supplied to the measured optical fiber 9 at each repetition period TA.

Therefore, in the above-described embodiment, the waveform data when the optical pulse is supplied to the optical fiber 9 to be measured at the repetition period T of the initially set range and the noise level indicating the detection limit level of the waveform signal are determined. In comparison, the repetition initially set to a value close to the noise level and larger than the time t of the sampling position farthest from the near end 9b of the measured optical fiber 9 and taking into account the zero sampling range as the optimum repetition period Ta. Since the period T is automatically corrected, regardless of the presence or absence of the secondary reflection, the repetition period of the synchronizing signal is automatically corrected and set to an optimum value, and an optical pulse is transmitted to the optical fiber 9 to be measured every repetition period. It can be supplied, and the troublesome setting performed by the measurer as in the related art is not required, and the operability can be improved. In addition, since the repetition period T is set to the optimum value, wasted time is reduced,
Measurement time can be reduced.

FIG. 4 is a block diagram showing a second embodiment of the optical pulse tester according to the present invention. The optical pulse tester according to this embodiment changes the repetition period of an optical pulse supplied to an optical fiber to be measured, and automatically determines an optimum repetition period based on a change in waveform data of a measurement range due to two different sets of repetition periods. The measurement range setting means 10, the range setting means 11, the timing generation means 2,
It comprises a light emitting element driving means 3, an E / O conversion means 4, an optical branching and coupling means 5, an O / E conversion means 6, a signal processing means 12, and a display means 8.

The measurement range setting means 10 sets the measurement range EA for performing measurement by displaying the reflected light (observation waveform) returning from the optical fiber 9 to be measured with the supply of the optical pulse on the display means 8 for measurement. In this measurement range EA, the point where the light pulse is emitted is set as the reference point P0.
As shown in FIG. 5A, the measurement range EA1 is set over the entire range of the observed waveform from the reference point P0, and FIG.
In some cases, a part of the waveform observation is set as the measurement range EA2 with a predetermined shift amount SF from the reference point P0 as shown in FIG.

The range setting means 11 performs sampling of the waveform data by the two sets of synchronizing signals in the signal processing means 12, so that two sets of the synchronizing signals are set according to the time of the measuring range EA set by the measuring range setting means 10. Is set to determine the repetition period T (T1, T2).

Here, the repetition period T is the shift amount SF,
The measurement range EA is determined based on the total time t of the zero data range EZ for removing the offset from the waveform data. As shown in FIG. 5A, the measurement range EA1 is set without the shift amount SF. If set, range setting means 1
In 1, the range is set as the total time t1 of the measurement range EA1 and the zero data range EZ as the first repetition cycle T1, and the time longer than the repetition cycle T1 by the predetermined time t2 as the next repetition cycle T2.

As shown in FIGS. 5B and 5C,
When the measurement range EA2 is set with the shift amount SF1 set, the total time t3 of the shift amount SF1, the measurement range EA2, and the zero data range EZ is set to the first repetition period T1.
The range is set by setting a time longer than the repetition cycle T1 by a predetermined time t2 as the next repetition cycle T2.

The zero data range EZ is a section EC from the end of the synchronization signal having no reflected light from the optical fiber 9 to be measured to the rising edge of the next synchronization signal when the range of the repetition period T is set. Is set automatically.

As shown in FIG. 4, the timing generating means 2 generates a synchronizing signal having a repetition period T according to the range set by the range setting means 11, and outputs this synchronizing signal to the light emitting element driving means 3 and the signal processing means 12. Output to

The light emitting element driving means 3 outputs a current pulse to the E / O conversion means 4 at, for example, a rising timing of the synchronizing signal inputted from the timing generating means 2.

The E / O conversion means 4 is, for example, an LD (Laser Diode).
ode), and outputs an optical pulse to the optical branching / coupling means 5 at, for example, the rising timing of the current pulse input from the light emitting element driving means 3.

The optical branching / coupling means 5 comprises, for example, a fiber coupler, an optical branching coupler, an optical directional coupler, an optical switch, etc., and emits an optical pulse from the E / O conversion means 4 to the optical fiber 9 to be measured. ing.

The O / E conversion means 6 is, for example, an APD (Avalan
The backscattered light and the Fresnel reflected light returning from the measured optical fiber 9 with the supply of the light pulse are received and detected, converted into an electric signal, and output to the signal processing means 12.

The signal processing means 12 comprises a first sampling means 12a, a second sampling means 12b, a data comparing means 12c, a range switching means 12d, and a repetition period determining means 12e.

The first sampling means 12a samples the electric signal in the measurement range EA at a predetermined sampling cycle based on the synchronizing signal of the repetition cycle T1 initially set by the range setting means 11, and obtains the signal by this sampling. Data comparing means 1 for comparing a plurality of waveform data
2c.

The second sampling means 12b converts the electric signal in the measurement range EA into the same sampling cycle as that of the first sampling means 12a based on the synchronizing signal of the repetition cycle T2 set after the repetition cycle T1 by the range setting means 11. And a plurality of waveform data obtained by this sampling are compared with the data comparing means 12c.
Output to

The data comparing means 12c compares two sets of waveform data input from the sampling means 12a and 12b, and outputs a mismatch signal S1 to the range switching means 12d when the two sets of waveform data are different. I have. Also,
When the two sets of waveform data match, a match signal S2 is output to the repetition period determination means 12e.

The range switching means 12d is the data comparing means 1
2c based on the mismatch signal S1 from the
In the two sets of synchronization signals initially set in step 1, the shorter repetition cycle is switched to a longer cycle than the other repetition cycle. That is, in the embodiment, of the repetition periods T1 and T2 of the two sets of synchronization signals initially set by the range setting unit 11, the repetition period T1 of the synchronization signal supplied to the first sampling unit 12a is the second one. Repetition period T2 of the synchronization signal supplied to the second sampling means.
Since the cycle is shorter, the shorter repetition cycle T1 is switched to a cycle T3 (> T2) longer than the other repetition cycle T2. The variable amount of the repetition period is arbitrarily changed (for example, multiplied by the square) in a stepwise manner.

The repetition cycle determining means 12e determines and sets the short cycle of the two sets of repetition cycles T1 and T2 as the repetition cycle based on the coincidence signal S2 from the data comparison means 12c.

Next, the operation of the optical pulse tester configured as described above will be described with reference to the timing charts of FIGS. 5A to 5C and the flowchart of FIG. First, as shown in FIG. 5A or 5C, a measurement range EA is set (ST11). Next, a range of repetition periods T1 and T2 (T1 <T2) of two sets of synchronization signals is set (ST12). Then, an optical pulse is supplied to the optical fiber 9 to be measured by a synchronization signal having a repetition period T1, and data of the reflected light returning from the optical fiber 9 to be measured is supplied in accordance with the supply of the optical pulse, thereby acquiring waveform data. (ST13). Subsequently, an optical pulse is supplied to the measured optical fiber 9 by a synchronization signal having a repetition period T2, and data sampling is performed on the reflected light from the measured optical fiber 9 to acquire waveform data (ST1).
4).

Next, the two sets of waveform data obtained by the synchronizing signals with the two sets of repetition periods T1 and T2 are converted into the measurement range EA.
(ST15). If the two sets of waveform data match and are identical (ST16-Yes), the shorter of the two sets of repetition cycles T1 and T2 is set as the optimum repetition cycle T1 (ST1).
7). If the two sets of waveform data are different (ST16-
No), the shorter repetition period T1 is switched to a period T3 longer than the other repetition period T2 (ST18), and an optical pulse is supplied to the optical fiber 9 to be measured by the repetition period T3, and the reflection from the optical fiber 9 is measured. Light data sampling is performed to capture waveform data (ST19).

Then, returning to the operation of ST15, the two sets of waveform data of the repetition period T3 and the repetition period T2 are compared.
The shorter repetition cycle T2 of the set of repetition cycles T2 and T3 is set as the optimum repetition cycle. if,
If the two sets of waveform data are different, the operation of switching the shorter repetition cycle to a longer cycle than the other repetition cycle and comparing the waveform data by the two sets of synchronization signals is repeated until the two sets of waveform data match. It is.

Here, in the example of FIG.
A1 is set over the entire range of the observed waveform from the reference point P0, and the secondary Fresnel reflection appears ahead of the Fresnel reflection at the far end 9a of the measured optical fiber 9 in the observed waveform.
The waveform data of the set of repetition periods T1 and T2 is different, the repetition period T1 is switched to a period T3 longer than the repetition period T2, and the waveform data of the repetition period T2 and the waveform data of the repetition period T3 are compared.

In the example of FIG. 5C, the measurement range EA
Since 2 is set at a position that does not include the secondary Fresnel reflection, the waveform data of the two sets of repetition cycles T1 and T2 are the same, and the shorter repetition cycle T1 is set as the optimum repetition cycle.

Therefore, in the above-described embodiment, two sets of waveform data having different repetition periods are set within the measurement range EA in order to capture a change in the observed waveform when the repetition period of the synchronization signal for determining the emission timing of the optical pulse is changed. When the two sets of waveform data match, the shorter of the two sets of repetition cycles is automatically set as the optimum repetition cycle of the optical pulse supplied to the optical fiber 9 to be measured. Can be set.

In general, an optical pulse tester converts a linear observation waveform into log data and displays the waveform to perform measurement. At this time, in order to remove an offset from the waveform data, the measurement is performed after the measurement range EA. Section E without signal
At C, zero data is taken and the difference from each waveform data is taken. However, since the displayed waveform is a log value, if the zero data shifts, a large distortion occurs in the observed waveform.

Therefore, in the optical pulse tester of this embodiment, even if the repetition period is inappropriate and the zero data contains a weak signal component, two sets of waveform data having different repetition periods are measured within the measurement range EA. As a result of the comparison, a large change appears in the waveform data, and the far end 9a of the optical fiber 9 to be measured.
Can be set to an optimum repetition period even if the waveform is embedded in noise.

Also, in the above-described embodiment, the two
When the sets of waveform data are different, an example has been described in which the shorter repetition cycle is made longer than the other repetition cycle and the repetition cycle is switched stepwise until the two sets of waveform data match to perform data comparison. Irrespective of the length L of the optical fiber 9 to be measured, a time longer than the distance over which the observed waveform can be detected and a time shorter than this time by a predetermined time are defined as two sets of repetition periods T initially set by the range setting means 11.
1, T2 (T1> T2). In this case, if the waveform data of the two sets of repetition cycles T1 and T2 are different, the longer repetition cycle T1 is set as the optimum repetition cycle, and the waveform data of the two sets of repetition cycles T1 and T2 are identical and identical. If so, the longer repetition cycle T1 is made shorter than the other repetition cycle T2, and the repetition cycle is switched stepwise until two sets of waveform data are different, and data comparison is performed.

[0063]

As described above, according to the first aspect of the present invention,
According to the optical pulse tester, the waveform data when an optical pulse is supplied to the optical fiber to be measured at the initially set repetition period T is compared with the noise level indicating the detection limit level of the waveform signal. Since the repetition period is automatically corrected as the optimum correction repetition period, a value larger and closer than the time of the sampling position farthest from the near end of the measured optical fiber exceeding the level is synchronized regardless of the presence or absence of secondary reflection. The optical pulse can be supplied to the optical fiber to be measured by automatically correcting and setting the signal repetition period to an optimal value, and the operability can be improved without the need for the operator to perform the troublesome setting as in the related art. In addition, since the repetition period is corrected and set to an optimum value, useless time can be reduced and measurement time can be reduced. Further, according to the optical pulse tester of the second and third aspects of the present invention, two different repetition periods are used.
By comparing the set of waveform data within the measurement range, the change in the observed waveform when the repetition period is changed is captured, and one repetition period is supplied to the optical fiber under measurement based on this change. It can be automatically set as the pulse repetition period.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining the operation of the optical pulse tester.

FIG. 3A is a timing chart of observation waveforms and optical pulses when secondary Fresnel reflection appears after far-end Fresnel reflection, and FIG. 3B is a timing chart when secondary Fresnel reflection does not appear after far-end Fresnel reflection. Timing chart of observation waveform and optical pulse

FIG. 4 is a block diagram showing a second embodiment of the optical pulse tester according to the present invention.

FIG. 5 is a timing chart of an optical pulse and an observed waveform for explaining the operation of the optical pulse tester.

FIG. 6 is a flowchart for explaining the operation of the optical pulse tester.

FIG. 7 is a block diagram of a conventional optical pulse tester.

FIG. 8 is a timing chart of an optical pulse and an observed waveform for explaining the operation of a conventional optical pulse tester.

[Explanation of symbols]

1 ... initial range setting means, 2 ... timing generation means, 7
a: data sampling means, 7b: noise level calculation means, 7c: data comparison means, 7d: sampling position calculation means, 7e: repetition period correction means, 9: optical fiber to be measured, 9b: near end, 10: measurement range setting Means, 11
... Range setting means, 12a first sampling means (sampling means), 12b second sampling means (sampling means), 12c data comparing means, 1
2d: range switching means, 12e: repetition cycle determination means, Ln: noise level, T: repetition cycle, TA: correction repetition cycle, EA: measurement range, P0: reference point, T
(T1, T2, T3): repetition period, S1: mismatch signal, S2: match signal.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 3-60375 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01M 11/00-11/02

Claims (3)

(57) [Claims] 1. When the observed waveform corresponds to a detectable distance
Data sampling means (7a) for sampling a waveform signal when an optical pulse is being supplied to the optical fiber to be measured (9) based on a synchronization signal having a repetition period (T) preset in advance over a longer period of time. A data comparing unit (7c) for comparing a plurality of waveform data sampled by the data sampling unit with a preset noise level (Ln) indicating a detection limit of the waveform signal; A sampling position calculating means (7d) for calculating a sampling position of waveform data farthest from a near end (9b) position of the measured optical fiber exceeding the noise level based on the result; and emitting an optical pulse to the measured optical fiber. The measured light
A value greater than and close to the time (t) for reciprocating to the sampling position calculated by the sampling position calculating means of the fiber is performed as a correction repetition period (TA).
And the calculated initial repetition period is calculated.
Repetition period correction means (7e) for setting the repetition period
An optical pulse tester comprising: 2. A device under test based on the timing of a synchronization signal.
With reference to the emission point of the optical pulse supplied to the optical fiber (9)
As a point (P0), the measurement range (E
Measuring range setting means (10) for setting A) and at least a time including the measuring range from the reference point.
Two different repetition periods of the synchronization signal in a long time
Range setting means (11) for setting (T1, T2); and two different sets of repetition cycles set by the range setting means.
The waveform signal from the measured optical fiber
Sampling means (12a, 12b) for ringing and two sets of waveform data by the sampling means are measured.
When the data comparing means (12c) for comparing within the range and the two sets of waveform data by the data comparing means do not match;
The shorter repetition cycle is longer than the other repetition cycle.
Range switching means ( 12d)
And the two sets of waveform data obtained by the data comparing means match.
Sometimes the shorter repetition cycle is the optimal repetition cycle
And a repetition period determining means (12e) for setting
An optical pulse tester characterized in that: 3. A device under test based on the timing of a synchronization signal.
With reference to the emission point of the optical pulse supplied to the optical fiber (9)
As a point (P0), the measurement range (E
Measuring range setting means (10) for setting A) and at least a time including the measuring range from the reference point.
Two different repetition periods of the synchronization signal in a long time
Range setting means (11) for setting (T1, T2); and two different sets of repetition cycles set by the range setting means.
The waveform signal from the measured optical fiber
Sampling means (12a, 12b) for ringing and two sets of waveform data by the sampling means are measured.
When the data comparison means (12c) for comparing within the range and the two sets of waveform data by the data comparison means match
The longer repetition period is shorter than the other
Range switching means (12d) for switching to a range with a shorter time
And that two sets of waveform data by the data comparing means do not match.
Sometimes the longer repetition cycle is the optimal repetition cycle
And a repetition period determining means (12e) for setting
An optical pulse tester characterized in that: