JP7766633B2 - Optical Time Domain Reflectometer - Google Patents

Description

This disclosure relates to an optical time domain reflectometer.

Conventionally, an OTDR (Optical Time Domain Reflectometer) is known as a device capable of measuring the condition of optical fiber. For example, Patent Document 1 discloses an OTDR measurement device capable of detecting breaks near the end of an optical fiber.

An OTDR repeatedly injects optical pulses into the optical fiber being measured, and can measure the condition of the optical fiber, such as breaks and losses, based on the intensity of the light reflected from the optical fiber and the time it takes to receive the reflected light from the optical fiber.

Japanese Patent Application Laid-Open No. 2008-20226

If the optical fiber being measured has a break, the light reflected at the break will have a greater optical intensity than the light reflected by Rayleigh scattering in the optical fiber. If the optical intensity is greater than a certain level, an excessive photocurrent may be supplied to the amplifier downstream of the photodetector that detects the reflected light, causing the amplifier output to saturate.

When the amplifier output saturates, the amplifier's response speed decreases, and the OTDR waveform measured by the OTDR degrades from the ideal waveform. In this specification, "OTDR waveform" refers to a waveform obtained by OTDR measurement, with the horizontal axis representing distance and the vertical axis representing light intensity. "Distance" corresponds to the time from when a light pulse is incident until the reflected light returns. "Light intensity" corresponds to the light intensity of the reflected light.

Figure 5 shows an example of an OTDR waveform measured with a conventional OTDR. Referring to Figure 5, in areas where the reflected light intensity is high, the actually measured OTDR waveform 501 is degraded from the ideal OTDR waveform 502 due to saturation of the amplifier output.

The present disclosure therefore aims to provide an optical time domain tester that can reduce degradation of the OTDR waveform even when receiving reflected light with high optical intensity during OTDR measurement.

According to some embodiments, an optical time domain reflectometer (OTDR) functions as an optical time domain reflectometer capable of measuring the state of an optical fiber, and includes a laser element that generates optical pulses that enter the optical fiber, a photodetector that detects reflected light from the optical fiber, an optical intensity adjuster that can adjust the intensity of the optical pulses and the reflected light, and a controller that controls the optical intensity adjuster. This type of optical time domain reflectometer can reduce degradation of the OTDR waveform even when receiving reflected light with a high optical intensity during OTDR measurement.

In one embodiment of the optical pulse tester, the light intensity adjustment unit may include a variable optical attenuator that can adjust the light intensity of the optical pulse and the reflected light. This makes it possible to adjust the light intensity of the optical pulse and the reflected light.

In one embodiment of the optical time domain tester, if the OTDR waveform of the reflected light detected by the optical receiver contains an optical intensity equal to or greater than a threshold, the control unit may increase the attenuation of the variable optical attenuator by a predetermined amount and measure the reflected light again. This allows measurements to be taken without saturating the amplifier output.

In one embodiment of the optical time domain tester, when the attenuation of the variable optical attenuator is increased by a predetermined amount, the control unit may generate a composite OTDR waveform by combining multiple OTDR waveforms of the reflected light measured at multiple different attenuation amounts. This allows a composite OTDR waveform to be generated by using OTDR waveform data measured at large attenuation amounts for areas with high light intensity, and OTDR waveform data measured at small attenuation amounts for areas with low light intensity.

In one embodiment, the optical time domain tester may further include a display unit, and the control unit may display the composite OTDR waveform on the display unit. This allows the user to check the composite OTDR waveform.

In one embodiment of the optical pulse tester, the light intensity adjustment unit may include a variable optical amplifier that can adjust the light intensity of the optical pulse and the reflected light. This makes it possible to adjust the light intensity of the optical pulse and the reflected light.

In one embodiment of the optical time domain tester, if the OTDR waveform of the reflected light detected by the optical receiver contains an optical intensity equal to or greater than a threshold, the control unit may reduce the amplification amount of the variable optical amplifier by a predetermined amount and measure the reflected light again. This allows measurements to be taken without saturating the amplifier output.

In one embodiment of the optical time domain tester, when the amplification amount of the variable optical amplifier is reduced by a predetermined amount, the control unit may generate a composite OTDR waveform by combining multiple OTDR waveforms of the reflected light measured with multiple different amplification amounts. This allows a composite OTDR waveform to be generated by using OTDR waveform data measured with a small amplification amount for areas with high light intensity, and using OTDR waveform data measured with a large amplification amount for areas with low light intensity.

In one embodiment, the optical time domain tester may further include a display unit, and the control unit may display the composite OTDR waveform on the display unit. This allows the user to check the composite OTDR waveform.

This disclosure provides an optical time domain tester that can reduce degradation of the OTDR waveform even when receiving reflected light with high optical intensity during OTDR measurement.

1 is a diagram illustrating a schematic configuration of an optical pulse tester according to an embodiment; FIG. 10 is a diagram showing an example of an OTDR waveform when the amount of attenuation is small. FIG. 10 is a diagram showing an example of an OTDR waveform when the amount of attenuation is large. FIG. 10 is a diagram showing an example of a composite OTDR waveform. FIG. 10 is a diagram showing a schematic configuration of an optical pulse tester according to a modified example. FIG. 1 is a diagram showing a schematic configuration of an optical pulse tester according to a comparative example. FIG. 1 is a diagram showing an example of a conventional OTDR waveform.

Figure 1 shows the schematic configuration of an optical time domain tester 10 according to one embodiment. The configuration and functions of the optical time domain tester 10 according to one embodiment will be described with reference to Figure 1.

The optical time domain reflectometer 10 is a measuring instrument that functions as an OTDR and can measure the state of the optical fiber 1. The optical time domain reflectometer 10 can measure the state of the optical fiber 1, such as breaks and loss, of the optical fiber 1 being measured. The optical time domain reflectometer 10 can be used, for example, when laying the optical fiber 1 and when performing maintenance and inspection of the optical fiber 1.

The optical fiber 1 to be measured may be, for example, an optical fiber used in an optical communication system that performs data communication using optical signals.

The optical pulse tester 10 can generate an OTDR waveform with distance on the horizontal axis and light intensity on the vertical axis by injecting an optical pulse into the optical fiber 1 and measuring the light intensity of the reflected light from the optical fiber 1. The "distance" on the horizontal axis corresponds to the time from when the optical pulse is injected until the reflected light returns. The "light intensity" on the vertical axis corresponds to the light intensity of the reflected light.

The light reflected at the break point in optical fiber 1 has a higher optical intensity than light reflected due to Rayleigh scattering, etc. By generating an OTDR waveform using the optical time domain reflectometer 10, it is possible to determine at what distance the light intensity is highest. This allows the optical time domain reflectometer 10 to measure the break point in optical fiber 1.

The optical pulse tester 10 includes a laser driver 11, an optical module 12, a light intensity adjuster 13, an amplifier 14, a sampling unit 15, a control unit 16, and a display unit 17.

The laser driver 11 is a driver that drives the laser element 121 provided in the optical module 12. The laser driver 11 drives the laser element 121 in response to commands from the control unit 16, causing the laser element 121 to generate optical pulses.

The optical module 12 includes a laser element 121, a half mirror 122, and a photodetector 123. The optical module 12 may house the laser element 121, the half mirror 122, and the photodetector 123 in the same case.

The laser element 121 generates laser light of a predetermined wavelength. It is sufficient for the laser element 121 to generate laser light of a constant light intensity. In other words, the laser element 121 does not need to be able to vary the light intensity. The laser element 121 is driven by the laser driver 11 to generate light pulses that are incident on the optical fiber 1.

The half mirror 122 transmits the light pulse incident from the laser element 121 and supplies it to the light intensity adjustment unit 13. The half mirror 122 reflects the reflected light incident from the light intensity adjustment unit 13 and supplies it to the light receiver 123.

Here, the reflected light is light that is reflected by the optical fiber 1, which is the object of measurement, after receiving an optical pulse from the optical pulse tester 10. The reflected light includes light reflected at a break in the optical fiber 1, light reflected by the optical fiber 1 due to Rayleigh scattering, etc.

The photodetector 123 detects the reflected light incident on the half mirror 122 and supplies a current signal corresponding to the light intensity of the reflected light to the amplifier 14. The photodetector 123 may be, for example, an avalanche photodiode (APD).

The light intensity adjustment unit 13 can adjust the light intensity of the light pulse incident from the half mirror 122 of the optical module 12. The light intensity adjustment unit 13 can adjust the light intensity of the reflected light incident from the optical fiber 1.

The light intensity adjustment unit 13 includes a variable optical attenuator 131 and an attenuator driver 132.

The variable optical attenuator 131 can adjust the optical intensity of the optical pulse incident from the half mirror 122 of the optical module 12. The variable optical attenuator 131 can adjust the optical intensity of the reflected light incident from the optical fiber 1. The attenuation amount of the variable optical attenuator 131 is set by the attenuator driver 132.

The attenuator driver 132 sets the attenuation amount of the variable optical attenuator 131 in response to commands from the control unit 16.

The amplifier 14 converts the current signal supplied from the optical receiver 123 of the optical module 12 into a voltage signal and amplifies the converted voltage signal. The amplifier 14 outputs the voltage signal to the sampling unit 15.

The sampling unit 15 samples the voltage signal supplied from the amplifier 14 at predetermined time intervals. The sampling unit 15 outputs the sampled signal to the control unit 16.

The control unit 16 includes at least one processor, at least one dedicated circuit, or a combination of these. The processor is a general-purpose processor such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), or a dedicated processor specialized for specific processing. The dedicated circuit is, for example, an FPGA (Field-Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). The control unit 16 controls each part of the optical time domain reflectometer 10 and executes processing related to the operation of the optical time domain reflectometer 10.

The control unit 16 controls the light intensity adjustment unit 13 and sets the attenuation amount of the variable optical attenuator 131. This allows the control unit 16 to adjust the light intensity of the light pulse incident from the half mirror 122 of the optical module 12. The control unit 16 can also adjust the light intensity of the reflected light incident from the optical fiber 1.

Details of the operation of the control unit 16 will be described later.

The display unit 17 includes one or more output interfaces that display information. The display unit 17 may include, for example, an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescent) display.

The display unit 17 can display the OTDR waveform generated by the control unit 16.

(Operation of the optical pulse tester)
Next, the operation of the optical pulse tester 10 will be described.

The control unit 16 controls the laser driver 11 to cause the laser element 121 to generate an optical pulse. The optical pulse generated by the laser element 121 is incident on the optical fiber 1 via the half mirror 122 and the variable optical attenuator 131.

At this time, the control unit 16 controls the attenuator driving unit 132 to set the attenuation amount of the variable optical attenuator 131 to a predetermined attenuation amount. As a result, the variable optical attenuator 131 attenuates the optical intensity of the optical pulse by the attenuation amount set by the control unit 16.

When an optical pulse is incident on optical fiber 1, light reflected at the break point in optical fiber 1, light reflected by Rayleigh scattering in optical fiber 1, and other light return to the optical time domain tester 10.

The reflected light incident on the optical pulse tester 10 from the optical fiber 1 is detected by the optical receiver 123 via the variable optical attenuator 131 and half mirror 122. At this time, the variable optical attenuator 131 attenuates the optical intensity of the reflected light by the attenuation amount set by the control unit 16.

The photoreceiver 123 supplies a current signal corresponding to the light intensity of the reflected light to the amplifier 14. The amplifier 14 converts the current signal supplied from the photoreceiver 123 of the optical module 12 into a voltage signal and amplifies the converted voltage signal. The sampling unit 15 samples the voltage signal supplied from the amplifier 14 at predetermined time intervals. The sampling unit 15 outputs the sampled signal to the control unit 16.

The control unit 16 processes the voltage signal acquired from the sampling unit 15 to generate an OTDR waveform. As described above, the OTDR waveform is a waveform with "distance" on the horizontal axis and "light intensity" on the vertical axis. "Distance" on the horizontal axis corresponds to the time from when a light pulse is incident on the optical fiber 1 until the reflected light returns. "Light intensity" on the vertical axis corresponds to the light intensity of the reflected light.

If the OTDR waveform generated based on the reflected light detected by the optical receiver 123 contains a light intensity equal to or greater than the threshold, the control unit 16 increases the attenuation of the variable optical attenuator 131 by a predetermined amount and measures the reflected light again.

The threshold value may be a value set based on the light intensity at which voltage signal saturation is expected to occur during signal processing in the amplifier 14. In other words, if the OTDR waveform contains light intensity equal to or greater than the threshold value, there is a possibility that voltage signal saturation will occur during signal processing in the amplifier 14.

The predetermined amount may be a preset amount. For example, the predetermined amount may be a few dB to several tens of dB.

The control unit 16 repeats the process of increasing the attenuation of the variable optical attenuator 131 by a predetermined amount and measuring the reflected light again until the generated OTDR waveform does not contain light intensity above the threshold.

When the control unit 16 increases the attenuation of the variable optical attenuator 131 by a predetermined amount and measures the reflected light again, it combines the multiple OTDR waveforms generated based on the reflected light measured at each attenuation to generate a composite OTDR waveform. In this embodiment, the term "composite OTDR waveform" is used to refer to a waveform generated by combining multiple OTDR waveforms.

The process of generating a composite OTDR will be described with reference to Figures 2A to 2C. Figure 2A is a diagram showing an example of an OTDR waveform when the attenuation of the variable optical attenuator 131 is small. Figure 2B is a diagram showing an example of an OTDR waveform when the attenuation of the variable optical attenuator 131 is large. Figure 2C is a diagram showing an example of a composite OTDR waveform obtained by combining the OTDR waveform shown in Figure 2A and the OTDR waveform shown in Figure 2B.

Referring to OTDR waveform A shown in Figure 2A, the tip of peak 201, where the optical intensity is high, is flat. This indicates that the signal input to amplifier 14 is large and the output of amplifier 14 is saturated.

When an OTDR waveform such as OTDR waveform A shown in Figure 2A is generated, the control unit 16 increases the attenuation of the variable optical attenuator 131 by a predetermined amount and measures the reflected light again. The OTDR waveform generated based on the reflected light measured again when the attenuation is large is OTDR waveform B shown in Figure 2B.

Referring to OTDR waveform B in Figure 2B, peak 203, where the light intensity is high, has a sharp peak at its tip. This indicates that the signal input to amplifier 14 has become smaller and the output of amplifier 14 is no longer saturated.

Furthermore, when comparing the width w1 of peak 201 in OTDR waveform A shown in Figure 2A with the width w2 of peak 203 in OTDR waveform B shown in Figure 2B, width w1 is wider than width w2. This indicates that in OTDR waveform A, where the output of amplifier 14 is saturated, the response speed of amplifier 14 has decreased, and the width w1 of peak 201 has widened.

In this way, by increasing the attenuation amount of the variable optical attenuator 131, the control unit 16 can generate an OTDR waveform B that includes a sharp peak 203 with a narrow width in the area where the optical intensity is high, as shown in Figure 2B.

On the other hand, comparing small signal portion 202, which is the portion of OTDR waveform A shown in Figure 2A where the light intensity is low, with small signal portion 204, which is the portion of OTDR waveform B shown in Figure 2B where the light intensity is low, it can be seen that small signal portion 202 was measured with a high signal-to-noise ratio, while small signal portion 204 has a lower signal-to-noise ratio. Small signal portion 202 and small signal portion 204 do not contain reflected light with a high light intensity, such as light reflected at a break point, and only contain reflected light due to Rayleigh scattering, etc.

In other words, in areas where the light intensity is low, it is preferable to measure with low attenuation, as this allows for a high signal-to-noise ratio.

The control unit 16 combines OTDR waveform A, which is generated with low attenuation as shown in FIG. 2A, with OTDR waveform B, which is generated with high attenuation as shown in FIG. 2B, to generate OTDR waveform C, as shown in FIG. 2C. OTDR waveform C is a combined OTDR waveform.

As shown in Figure 2C, OTDR waveform C is a waveform synthesized by using the waveform data of OTDR waveform B for areas with high light intensity and the data of OTDR waveform A for areas with low light intensity.

When the control unit 6 generates a composite OTDR waveform as shown in Figure 2C, it displays the composite OTDR waveform on the display unit 17.

The optical time domain tester 10 according to one embodiment described above can reduce degradation of the OTDR waveform even when receiving reflected light with high optical intensity during OTDR measurement. More specifically, the optical time domain tester 10 includes an optical intensity adjuster 13 that can adjust the optical intensity of the optical pulse and reflected light, and a controller 16 that controls the optical intensity adjuster 13. When the OTDR waveform contains an optical intensity equal to or greater than a threshold, the controller 16 controls the optical intensity adjuster 13 to attenuate the optical intensity of the optical pulse and reflected light. This prevents the output of the amplifier 14 from saturating due to high optical intensity of the optical pulse and reflected light, thereby reducing degradation of the OTDR waveform even when receiving reflected light with high optical intensity.

(Modification)
3 is a diagram showing a schematic configuration of an optical pulse tester 10a according to a modified example, which will be described with reference to FIG.

The optical pulse tester 10a according to this modification includes a laser driver 11, an optical module 12, a light intensity adjuster 18, an amplifier 14, a sampling unit 15, a control unit 16, and a display unit 17.

Compared to the optical pulse tester 10 shown in FIG. 1, the optical pulse tester 10a according to this modified example differs from the optical pulse tester 10 shown in FIG. 1 in that it has an optical intensity control unit 18 instead of the optical intensity control unit 13.

For the modified optical time domain tester 10a, the differences from the optical time domain tester 10 shown in Figure 1 will be mainly described, and the common and similar aspects to the optical time domain tester 10 shown in Figure 1 will be omitted where appropriate.

The light intensity adjustment unit 18 includes a variable optical amplifier 181 and an amplifier driver 182.

The variable optical amplifier 181 can adjust the optical intensity of the optical pulses incident from the half mirror 122 of the optical module 12. The variable optical amplifier 181 can adjust the optical intensity of the reflected light incident from the optical fiber 1. The amplification amount of the variable optical amplifier 181 is set by the amplifier driver 182.

In this way, while the variable optical attenuator 131 of the optical pulse tester 10 shown in Figure 1 can adjust the light intensity by setting the attenuation amount, the variable optical amplifier 181 of the optical pulse tester 10a in the comparative example can adjust the light intensity by setting the amplification amount.

The variable optical amplifier 181 may be, for example, an SOA (Semiconductor Optical Amplifier).

The amplifier driver 182 sets the amplification amount of the variable optical amplifier 181 in response to commands from the control unit 16.

If the OTDR waveform generated based on the reflected light detected by the optical receiver 123 contains a light intensity above a threshold, the control unit 16 reduces the amplification amount of the variable optical amplifier 181 by a predetermined amount and measures the reflected light again.

The control unit 16 repeats the process of reducing the amplification amount of the variable optical amplifier 181 by a predetermined amount and measuring the reflected light again until the generated OTDR waveform does not contain light intensity above the threshold.

When the control unit 16 reduces the amplification amount of the variable optical amplifier 181 by a predetermined amount and measures the reflected light again, it combines multiple OTDR waveforms generated based on the reflected light measured at each amplification amount to generate a composite OTDR waveform.

Once the control unit 16 generates the composite OTDR waveform, it causes the display unit 17 to display the composite OTDR waveform.

In this way, in the optical time domain tester 10a according to the modified example, when the OTDR waveform contains an optical intensity equal to or greater than the threshold, the control unit 16 reduces the amplification amount of the variable optical amplifier 181 by a predetermined amount. Therefore, like the optical time domain tester 10 shown in FIG. 1, the optical time domain tester 10a according to the modified example can prevent the output of the amplifier 14 from saturating, thereby reducing degradation of the OTDR waveform even when receiving reflected light with a high optical intensity.

The optical pulse tester 10a according to the modified example also includes a variable optical amplifier 181, which can amplify optical pulses incident from the half mirror 122 of the optical module 12. This improves the dynamic range of the OTDR waveform. Furthermore, because the optical pulses generated by the laser element 121 can be low-power, the laser element 121 does not need to be capable of generating high-power optical pulses. Therefore, the optical pulse tester 10a according to the comparative example can broaden the options for the laser element 121.

(Comparative Example)
4 is a diagram showing a schematic configuration of an optical pulse tester 200 according to a comparative example. The optical pulse tester 200 according to the comparative example will be described with reference to FIG.

The optical pulse tester 200 according to the comparative example includes a laser driver 11, an optical module 12, an amplifier 14, a sampling unit 15, a control unit 16, and a display unit 17.

The optical pulse tester 200 according to the comparative example differs from the optical pulse tester 10 shown in Figure 1 in that it does not include the optical intensity regulator 13.

The optical pulse tester 200 of the comparative example does not have a light intensity adjuster 13. Therefore, if the OTDR waveform generated based on the reflected light detected by the optical receiver 123 contains a light intensity above the threshold, the amplification factor of the amplifier 14 is set to a low value, and the light intensity of the optical pulse generated by the laser element 121 is set to a low value, and the OTDR waveform is measured again.

The optical time domain tester 200 according to the comparative example has the following four problems:

<Challenge 1>
When the OTDR waveform contains optical intensities above the threshold, even if the amplification factor of amplifier 14 is set to a small value, if an excessively large current signal is supplied from optical receiver 123 to amplifier 14, the output of amplifier 14 will saturate, resulting in a decrease in response speed. When the output of amplifier 14 saturates, the resulting waveform will be something like OTDR waveform 501 shown in Figure 5, which is degraded from the ideal OTDR waveform 502. Therefore, in optical time domain tester 200 according to the comparative example, the waveform reproducibility and dead zone performance will also deteriorate.

<Challenge 2>
When the OTDR waveform includes a light intensity equal to or greater than a threshold, if the light intensity of the light pulse generated by the laser element 121 is reduced, the center wavelength of the light pulse will be shifted.

<Challenge 3>
The optical pulse tester 200 according to the comparative example adjusts the amplification factor of the amplifier 14 according to the intensity of the reflected light, which may result in a decrease in the signal-to-noise ratio.

<Challenge 4>
When the OTDR waveform contains a light intensity equal to or greater than a threshold, the adjustment takes time because two parameters, the amplification degree of the amplifier 14 and the light intensity of the light pulse generated by the laser element 121, are adjusted.

The optical time domain tester 10 shown in Figure 1 can solve problems 1 to 4 described above with the optical time domain tester 200 according to the comparative example.

To address issue 1, the optical time domain tester 10 shown in Figure 1 can attenuate the optical intensity of the optical pulse and the optical intensity of the reflected light using the variable optical attenuator 131 when there is reflected light with a high optical intensity during OTDR measurement. This reduces the magnitude of the current signal supplied to the amplifier 14 and prevents the amplifier 14 output from saturating, thereby improving waveform reproducibility.

To address issue 2, the optical time domain tester 10 shown in Figure 1 can maintain a constant optical intensity of the optical pulses generated by the laser element 121 without needing to reduce the optical intensity of the optical pulses generated by the laser element 121, even when receiving reflected light with a high optical intensity during OTDR measurement. Therefore, the optical time domain tester 10 shown in Figure 1 can prevent the center wavelength of the optical pulses generated by the laser element 121 from shifting.

To address issue 3, the optical time domain tester 10 shown in Figure 1 can set the gain of the amplifier 14 to a constant level regardless of the intensity of the reflected light, thereby maintaining the signal-to-noise ratio at a desired level.

To address issue 4, the optical time domain tester 10 shown in Figure 1 only needs to adjust the light intensity adjustment unit 13 when there is reflected light with a high optical intensity during OTDR measurement, thereby reducing the time required for adjustment.

It will be apparent to those skilled in the art that the present disclosure may be embodied in other forms than the above-described embodiments without departing from the spirit or essential characteristics thereof. Therefore, the foregoing description is illustrative and not limiting. The scope of the disclosure is defined by the appended claims, not by the foregoing description. All modifications within the scope of their equivalents are intended to be encompassed therein.

For example, the arrangement and number of each component described above are not limited to the above description and the illustrations in the drawings. The arrangement and number of each component may be configured arbitrarily as long as the component functions can be realized.

For example, in the above-described embodiment, the optical module 12 is configured to include a laser element 121, a half mirror 122, and a photodetector 123, but the optical module 12 may further include a lens for collimating the optical pulses into collimated light.

For example, in the description of the optical time domain tester 10a according to the above-mentioned modification, when the OTDR waveform contains an optical intensity above the threshold, the control unit 16 reduces the amplification amount of the variable optical amplifier 181 by a predetermined amount and measures the reflected light again. However, the optical time domain tester 10a according to the modification may perform an operation to increase the amplification amount by a predetermined amount instead of decreasing the amplification amount by a predetermined amount. In this case, the control unit 16 sets the amplification amount of the variable optical amplifier 181 to a small value as the initial value, and then increases the amplification amount by a predetermined amount until the OTDR waveform contains an optical intensity above the threshold, and measures the reflected light again.

REFERENCE SIGNS LIST 1 Optical fiber 10, 10a Optical time domain reflectometer 11 Laser driver 12 Optical module 13 Light intensity adjuster 14 Amplifier 15 Sampling unit 16 Control unit 17 Display unit 18 Light intensity adjuster 121 Laser element 122 Half mirror 123 Photoreceiver 131 Variable optical attenuator 132 Attenuator driver 181 Variable optical amplifier 182 Amplifier driver 200 Optical time domain reflectometer

Claims (7)

An optical time domain reflectometer (OTDR) capable of measuring the state of an optical fiber,
a laser element that generates optical pulses that are incident on the optical fiber;
a light receiver for detecting reflected light from the optical fiber;
a light intensity adjusting unit that adjusts the light intensity of the light pulse and the reflected light;
a control unit that controls the light intensity adjustment unit;
Equipped with
the light intensity adjusting unit includes a variable optical attenuator capable of adjusting the light intensity of the optical pulse and the reflected light,
When the OTDR waveform of the reflected light detected by the optical receiver contains an optical intensity equal to or greater than a threshold, the control unit increases the attenuation of the variable optical attenuator by a predetermined amount and measures the reflected light again . 2. The optical pulse tester according to claim 1 ,
When the attenuation of the variable optical attenuator is increased by a predetermined amount, the control unit synthesizes multiple OTDR waveforms of the reflected light measured at multiple different attenuation amounts to generate a synthesized OTDR waveform. 3. The optical pulse tester according to claim 2 ,
Further comprising a display unit,
The control unit causes the display unit to display the composite OTDR waveform. An optical time domain reflectometer (OTDR) capable of measuring the state of an optical fiber,
a laser element that generates optical pulses that are incident on the optical fiber;
a light receiver for detecting reflected light from the optical fiber;
a light intensity adjusting unit that adjusts the light intensity of the light pulse and the reflected light;
a control unit that controls the light intensity adjustment unit;
Equipped with
The optical pulse tester, wherein the optical intensity adjuster includes a variable optical amplifier that can adjust the optical intensity of the optical pulse and the reflected light. 5. The optical pulse tester according to claim 4 ,
When the OTDR waveform of the reflected light detected by the optical receiver contains an optical intensity equal to or greater than a threshold, the control unit reduces the amplification amount of the variable optical amplifier by a predetermined amount and measures the reflected light again. 6. The optical pulse tester according to claim 5 ,
When the amplification amount of the variable optical amplifier is reduced by a predetermined amount, the control unit synthesizes multiple OTDR waveforms of the reflected light measured at multiple different amplification amounts to generate a composite OTDR waveform. 7. The optical pulse tester according to claim 6 ,
Further comprising a display unit,
The control unit causes the display unit to display the composite OTDR waveform.