JP2009281813A - Optical fiber measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber measuring device can improve a response distance without increasing cost and deteriorating user's convenience, by changing only a pulse width of pulsing light without changing a frequency of the pulsing light entering the optical fiber. <P>SOLUTION: This optical fiber measuring device 1 includes: a laser light source 11 for outputting pulsing light L1 intended to enter an optical fiber 30; a photodetector 15 for receiving back scattered light L2 obtained by allowing the pulsing light L1 output from the laser light source 11 to enter the optical fiber 30; and a duty ratio adjuster 21 for adjusting a duty ratio of the pulsing light L1 output from the laser light source 11, and measures prescribed physical quantities such as a loss in the length direction of the optical fiber 30, a temperature or a strain, based on a received light signal S1 output from the photodetector 15. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical fiber measuring apparatus that measures the distribution of loss, temperature, strain, and the like in the length direction of an optical fiber.

  As is well known, an optical fiber measurement device measures the distribution of loss, temperature, strain, etc. in the length direction of an optical fiber by measuring the scattered light generated in the optical fiber by entering pulsed light into the optical fiber. Device. Since the optical fiber measurement device uses the optical fiber itself as a medium for measuring loss, temperature, strain, etc., it is possible to measure with a simple configuration compared to the measurement device that arranges and measures many point sensors. There is an advantage of being. One of the typical optical fiber measuring devices is an OTDR (Opticai Time Domain Reflectometer).

  In Patent Document 1 below, pulsed light is incident on an optical fiber to generate backward Raman scattered light, Stokes light and anti-Stokes light included in the backward Raman scattered light are individually received, and the Stokes light and anti-Stokes light are reflected. A technique for obtaining the temperature of a measurement point by calculating the intensity ratio of a received light signal with Stokes light is disclosed. With this technology, it is possible to measure the temperature distribution in the length direction of the optical fiber by changing the position of the measurement point in the length direction of the optical fiber by changing the light reception timing of Stokes light and anti-Stokes light. is there.

In addition, the following non-patent documents include a correlation with a light reception signal obtained by entering an optical fiber with an optical pulse train code-modulated using a Barker code or the like and receiving scattered light from the optical fiber. A technique for improving the SN ratio (signal-to-noise ratio) by performing processing (demodulation) is disclosed.
Japanese Patent No. 3106443 Nazarathy Moshe, Newton Steven A., Giffard RP, Moberly DS, Sischka F., Turtna・ Written Earl Junior (Trutna WR Jr.), Foster S (Foster S.), “Real-time long range complementary reflectometer (Real-time long range complementary meter) correlation optical time domain reflectometer), Journal of Lightwave Technology, January 1989, Vol. 7, p. 24-38

  By the way, as described above, the optical fiber measurement device measures scattered light sequentially generated at different points in the optical fiber while propagating the pulsed light along the optical fiber. For this reason, when the pulse width of the pulsed light incident on the optical fiber is wide, scattered light is generated from a plurality of different points in the optical fiber at a time, and the resolution is lowered. As a result, there is a problem that the response distance of the measurement result of the optical fiber measuring device depends on the pulse width of the pulsed light. Here, the “response distance” is a distance required for a change between 10% and 90% of the change Δ when there is a change Δ of a certain measurement result. If this response distance is short, the position where the change has occurred can be specified accurately. Conversely, if the response distance is long, it is difficult to specify the position.

  The simplest method for solving the above problem is to generate pulsed light having a narrow pulse width by increasing the frequency for generating pulsed light. For example, when pulse light having a pulse width of 10 nsec at a frequency of 100 MHz is generated, the response distance can be improved by generating pulse light having a pulse width of 3.3 nsec at a frequency of 300 MHz. However, when the frequency for generating pulsed light is increased, the following two problems arise.

  The first problem is that when the frequency for generating pulsed light is increased, an A / D (analog / digital) converter capable of high-speed sampling is required in a light receiving device that receives scattered light generated by an optical fiber. It is. Such an A / D converter is not suitable for processing a light reception signal of minute backscattered light because the number of effective bits is small, and the cost increases because it is expensive.

  The second problem is that when the frequency for generating pulsed light changes, the sampling frequency in the above light receiving device also needs to be changed, so that the position of the measurement point in the length direction of the optical fiber changes. . For example, a situation occurs in which the point that was the seventh measurement point before changing the response distance becomes the tenth measurement point by changing the response distance. For this reason, the consistency of the measurement data obtained before and after changing the response distance is difficult to obtain, and the convenience for the user is deteriorated.

  The present invention has been made in view of the above circumstances, and by changing only the pulse width of the pulsed light without changing the frequency of the pulsed light incident on the optical fiber, the cost is increased and the convenience of the user is deteriorated. An object of the present invention is to provide an optical fiber measuring apparatus capable of improving the response distance without any problems.

In order to solve the above-described problems, an optical fiber measurement device of the present invention includes a light source (11) that outputs pulsed light (L1) to be incident on an optical fiber (30), and pulsed light output from the light source. A light receiver (15, 71a, 71b) for receiving backscattered light (L2) obtained by being incident on the optical fiber, and the length of the optical fiber based on the light reception signal (S1) output from the light receiver. The optical fiber measuring devices (1 to 4) that measure a predetermined physical quantity in the vertical direction are characterized by including adjusters (21, 51) that adjust the duty ratio of the pulsed light output from the light source.
According to the present invention, the pulsed light whose duty ratio is adjusted by the regulator is output from the light source, is incident on the optical fiber, and propagates in the optical fiber, thereby generating backscattered light in the optical fiber. When light enters the light receiver, it is converted into a light reception signal, and a predetermined physical quantity in the length direction of the optical fiber is measured based on this light reception signal.
The optical fiber measurement apparatus of the present invention further includes a timing processor (20) that outputs a timing signal (TM1) that defines rising and falling timings of the pulsed light output from the light source. The device adjusts the rising and falling timings of the timing signal output from the timing processor using a predetermined threshold value.
Further, the optical fiber measuring apparatus of the present invention is characterized in that the predetermined threshold value used in the adjuster can be set to a different value depending on a duty ratio of pulsed light to be incident on the optical fiber. Yes.
Moreover, the optical fiber measuring device of the present invention includes a measuring instrument (52) for measuring a duty ratio of pulsed light to be output from the light source using a timing signal via the adjuster, and a measurement result of the measuring instrument. And a control device (53) for performing feedback control of the regulator.
The optical fiber measurement device of the present invention includes a code modulator (60) that performs a predetermined code modulation on the timing signal output from the timing processor and outputs the code signal to the adjuster, and a light receiver. And a correlation processing unit (61, 75) that performs demodulation by performing correlation processing on the received light-receiving signal.
In the optical fiber measuring apparatus of the present invention, the code modulator performs code modulation for converting the timing signal output from the timing processor into an RZ signal composed of a predetermined code string.

  According to the present invention, pulsed light whose duty ratio is adjusted by the adjuster is output from the light source and incident on the optical fiber to generate backscattered light in the optical fiber, and the backscattered light is received by the light receiver. Then, it is converted into a light reception signal, and a predetermined physical quantity in the length direction of the optical fiber is measured based on this light reception signal. For this reason, only the pulse width of the pulsed light can be changed without changing the frequency of the pulsed light incident on the optical fiber, and the response distance can be improved without increasing the cost and deteriorating the convenience for the user. effective.

  Hereinafter, an optical fiber measuring device according to an embodiment of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a main configuration of an optical fiber measuring device according to a first embodiment of the present invention. As shown in FIG. 1, the optical fiber measuring apparatus 1 of this embodiment includes a laser light source 11 (light source), a beam splitter 12, an optical fiber 13, a wavelength separator 14, a photodetector 15 (light receiver), an amplifier 16, and an A. A / D converter 17, an averager 18, a signal processor 19, a timing processor 20, a duty ratio adjuster 21 (adjuster), and a laser driver 22 are provided.

  The optical fiber measuring apparatus 1 having the configuration shown in FIG. 1 is generally called OTDR, and receives backscattered light obtained by, for example, incident pulsed light L1 on an optical fiber 30 that is a silica-based single mode fiber. Then, a predetermined physical quantity in the length direction of the optical fiber 30 is measured, and the measurement result is output to a personal computer (PC) 40. In the present embodiment, the case where the optical fiber measurement device 1 measures the loss of the optical fiber 30 as the predetermined physical quantity will be described as an example.

  The laser light source 11 includes a semiconductor laser element such as a DFB laser (Distributed feedback laser) and is driven by a laser driver 22 to output pulsed light L1 having a predetermined pulse width. Although described in detail later, the duty ratio of the pulsed light L1 output from the laser light source 11 is adjusted by the duty ratio adjuster 21. Here, the duty ratio refers to the ratio of the pulse width of the pulsed light L1 to one cycle of the pulsed light L1.

  The beam splitter 12 transmits the pulsed light L1 output from the laser light source 11 and reflects the return light L2 from the optical fiber 30 via the optical fiber 13 toward the wavelength separator 14. Here, the return light L2 from the optical fiber 30 includes scattered light such as backward Rayleigh scattered light and backward Raman scattered light, and Fresnel reflected light. The optical fiber 13 guides the pulsed light from the laser light source 11 transmitted through the beam splitter 12 to the optical fiber connection terminal Q1, and also returns the return light L2 from the optical fiber 30 input through the optical fiber connection terminal Q1 to the beam splitter. 12 leads to. As the optical fiber 13, similarly to the optical fiber 30, a quartz-based single mode fiber can be used.

  The wavelength separator 14 separates only the light in the wavelength range necessary for measuring the loss distribution of the optical fiber 30 from the return light L2 from the optical fiber 30 input through the optical fiber connection terminal Q1, Remove light in unnecessary wavelength range. The photodetector 15 converts the light in the wavelength region separated by the wavelength separator 14 into an electrical signal (light reception signal S1) and outputs the electrical signal to the amplifier 16. Here, since the return light L2 from the optical fiber 30 (particularly the Raman scattered light included in the return light L2) is extremely weak, a highly sensitive avalanche photodiode (hereinafter referred to as APD) is used as the photodetector 15. It is often done. By increasing the applied voltage (reverse bias) to the APD, the degree of multiplication can be increased, thereby making the photodetector 15 highly sensitive.

  The amplifier 16 amplifies the light reception signal S1 output from the photodetector 15 with a predetermined amplification factor and outputs the amplified signal to the A / D converter 17. The A / D converter 17 samples the light reception signal output from the amplifier 16 in synchronization with the timing signal TM2 output from the timing processor 20, converts it to a digital signal (light reception data), and averages the signal. Output to. The sampling frequency of the A / D converter 17 is, for example, about 50 MHz.

  The averager 18 operates in synchronization with the timing signal TM2 from the timing processor 20, and averages the received light data output from the A / D converter 17 every time the pulsed light L1 is incident on the optical fiber 30. Process. Here, when the optical fiber 30 is tested, the pulsed light is repeatedly incident multiple times, as described above, since the return light L2 from the optical fiber 30 is extremely weak, the received light data is input multiple times. This is to improve the S / N ratio (signal to noise ratio) by acquiring and averaging. The received light data output from the A / D converter 17 is time-series data indicating the intensity change of the return light from the optical fiber 30.

  The signal processor 19 operates in synchronization with the timing signal TM2 from the timing processor 20, and performs level correction processing and other arithmetic processing on the received light data that has been averaged by the averager 18. Thus, the loss distribution in the length direction of the optical fiber 30 is obtained. Data indicating the loss distribution obtained by the signal processor 19 can be output to the outside via the output terminal Q2. By taking the data output from the output terminal Q2 into the PC 40, the loss distribution in the length direction of the optical fiber 30 obtained by the signal processor 19 is displayed on the PC 40. The optical fiber measuring device 1 may be provided with a display device such as a CRT (Cathod Ray Tube) or a liquid crystal display device, and the measurement result of the signal processor 19 may be displayed on these display devices.

  The timing processor 20 includes a timing signal TM1 that defines the rising and falling timing of the pulsed light L1 output from the laser light source 11, the sampling timing of the A / D converter 17, the averaging unit 18 and the signal processing unit 19. A timing signal TM2 that defines the processing timing is output. The duty ratio adjuster 21 adjusts the rise and fall timings of the timing signal TM1 output from the timing processor 20 by using a predetermined threshold value, so that the duty of the pulsed light L1 output from the laser light source 11 is adjusted. Adjust the ratio. The laser driver 22 drives the laser light source 11 based on the timing signal TM1 in which the rising and falling timings are adjusted by the duty ratio adjuster 21.

  FIG. 2 is a timing chart for explaining the processing performed by the duty ratio adjuster 21. In FIG. 2, a waveform WF1 is an example of a waveform of the timing signal TM1 output from the timing processor 20, and waveforms WF2 and WF3 are examples of a waveform of a signal output from the duty ratio adjuster 21. In FIG. 2, time is plotted on the horizontal axis and voltage V is plotted on the vertical axis. Here, the waveform WF2 is a waveform of a signal output from the duty ratio adjuster 21 when the duty ratio of the pulsed light L1 emitted from the laser light source 11 is 50%, and the waveform WF3 is emitted from the laser light source 11. This is a waveform of a signal output from the duty ratio adjuster 21 when the duty ratio of the pulsed light L1 is 30%.

  As shown in FIG. 2, the waveform WF1 of the timing signal TM1 output from the timing processor 20 has a substantially rectangular wave shape having a rise time TR and a fall time TF. Further, threshold values TH1 and TH2 are set for the timing signal TM1. The threshold TH1 is a threshold set by the duty ratio adjuster 21 when the duty ratio of the pulsed light L1 is 50%, and the threshold TH2 is the duty ratio adjuster 21 when the duty ratio of the pulsed light L1 is 30%. Is the threshold value set in.

  The duty ratio adjuster 21 outputs a signal when the voltage of the timing signal TM1 output from the timing processor 20 increases beyond the threshold, and when the voltage of the timing signal TM1 decreases beyond the threshold. Stop the signal. Specifically, when the threshold value TH1 is set, a signal is output at time t11 when the voltage of the timing signal TM1 exceeds the threshold value TH1, and the voltage of the timing signal TM1 decreases beyond the threshold value TH1. The signal is stopped at time t12. Thereby, the waveform WF2 in FIG. 2 is obtained. Similarly, when the threshold value TH2 is set, a signal is output at time t21 when the voltage of the timing signal TM1 exceeds the threshold value TH2, and the voltage of the timing signal TM1 decreases beyond the threshold value TH2. The signal is stopped at time t22. Thereby, the waveform WF3 in FIG. 2 is obtained.

  Similar to the waveform WF1 of the timing signal TM1 output from the timing processor 20, the waveforms WF2 and WF3 of the signal output from the duty ratio adjuster 21 have a substantially rectangular wave shape having the rising time TR and the falling time TF. . For this reason, the waveforms WF2 and WF3 of the signal output from the duty ratio adjuster 21 do not rise abruptly even if signals are output at times t11 and t21, and the rising is completed after the rising time TR has elapsed. Similarly, even if the signal is stopped at times t12 and t22, the signal does not fall abruptly, and the fall is completed after the fall time TF has elapsed. In FIG. 2, the output times t11 and t21 from the duty ratio adjuster 21 are described as different times. However, this is for convenience of explanation, and in the actual operation, the timing processor 20 outputs By appropriately adjusting the timing signal TM1 to be performed, it is possible to operate so that t11 and t21 are at the same time.

  Here, an intermediate voltage value between the minimum voltage value and the maximum voltage value of the signal output from the duty ratio adjuster 21 is set as an intermediate value, and the voltage at the next rising edge from the time when the voltage value becomes the intermediate value at a certain rising edge. The time until the value reaches the intermediate value is defined as one cycle. Also, the time from when the voltage value becomes an intermediate value at a certain rising edge of the signal output from the duty ratio adjuster 21 until the voltage value becomes the intermediate value at the next falling edge is defined as a pulse width.

  When the threshold value TH1 is set in the duty ratio adjuster 21, as shown in FIG. 2, the duty ratio adjuster 21 has a signal having a pulse width of half of one cycle (a waveform WF2 having a duty ratio of 50%). Signal) is output. On the other hand, when the threshold value TH2 is set in the duty ratio adjuster 21, as shown in FIG. 2, the duty ratio adjuster 21 outputs a signal whose pulse width is 30% of one cycle (the duty ratio is 30%). A signal having a certain waveform WF3) is output. In this way, by setting a predetermined threshold for the duty ratio adjuster 21, the rising and falling timings of the timing signal TM1 output from the timing processor 20 can be adjusted according to the threshold. it can.

  Next, the operation at the time of measurement using the optical fiber measuring device 1 having the above configuration will be described. First, the user sets a threshold value for the duty ratio adjuster 21 in advance before starting measurement. In the following description, the case where the threshold value TH2 in FIG. 2 for setting the duty ratio of the pulsed light L1 to 30% is set will be described as an example. When the above settings are made and the measurement operation by the optical fiber measurement device 1 is started by a user instruction, the timing processor 20 outputs the timing signal TM1. The timing signal TM1 is input to the duty ratio adjuster 21, and the rising and falling timing adjustment is performed using a threshold set by the user.

  That is, when the voltage of the timing signal TM1 exceeds the threshold value TH2 (for example, at time t21 in FIG. 2), a signal is output from the duty ratio adjuster 21, and the voltage of the timing signal TM1 exceeds the threshold value TH2. The signal output from the duty ratio adjuster 21 is stopped at the time when it becomes smaller (for example, at time t22 in FIG. 2). Thus, a signal having the waveform WF3 in FIG. 2 is output from the duty ratio adjuster 21 to the laser driver 22. The laser driver 22 drives the laser light source 11 based on the signal from the duty ratio adjuster 21, whereby the laser light source 11 outputs pulsed light L 1 having a duty ratio of 30%.

  The pulsed light L1 output from the laser light source 11 enters the optical fiber 30 from the optical fiber connection terminal Q1 through the beam splitter 12 and the optical fiber 13 in order, and propagates through the optical fiber 30. When the pulsed light incident on the optical fiber 30 propagates through the optical fiber 30, backscattered light such as backward Rayleigh scattered light and backward Raman scattered light is generated. When the pulsed light reaches the other end of the optical fiber 30, Fresnel reflection occurs. Light is generated. The return light including the backscattered light and the Fresnel reflected light enters the optical fiber measuring device 1 from the optical fiber connection terminal Q1, and is passed through the optical fiber 13 and the beam splitter 12 in this order in an unnecessary wavelength region by the wavelength separator 14. After being removed, only the light of a predetermined wavelength range required is separated and then incident on the photodetector 15 to be converted into a light reception signal S1.

  The light reception signal S1 output from the photodetector 15 is amplified by the amplifier 16, and then input to the A / D converter 17 and sampled in synchronization with the timing signal TM2 output from the timing processor 20. Is converted into received light data of a digital signal. The received light data converted by the A / D converter 17 is input to the averager 18 and temporarily stored. The laser light source 11 outputs the pulsed light L1 each time the timing signal TM1 is output from the timing processor 20, and the light reception data sequentially output from the A / D converter 17 is input to the averager 18. To be averaged. The operation of making the above pulsed light L1 incident on the optical fiber 30 to acquire the received light data and performing the averaging process is repeated about tens of thousands of times.

  The received light data averaged by the averaging processing unit 31 is input to the signal processor 19 and subjected to level correction processing and other arithmetic processing, and the loss of the optical fiber 30 is obtained from the intensity of the backscattered light. It is done. The obtained losses are arranged in the order of sampling of the A / D converter 17, thereby obtaining a loss distribution in the length direction of the optical fiber 30. Data indicating the loss distribution obtained by the signal processor 19 is output from the output terminal Q2 to the outside and taken into the PC 40, and the loss distribution in the length direction of the optical fiber 30 is displayed on the PC 40.

  The operation in the case where the threshold value TH2 in FIG. 2 is set in the duty ratio adjuster 21 and the duty ratio of the pulsed light L1 is set to 30% has been described above, but by changing the threshold value set in the duty ratio adjuster 21. The duty ratio of the pulsed light L1 can be arbitrarily changed. For example, if the threshold value TH1 in FIG. 2 is set in the duty ratio adjuster 21, the duty ratio of the pulsed light L1 can be set to 50%.

  FIG. 3 is a diagram illustrating an example of the measurement result of the loss distribution. In FIG. 3, the loss distribution XD1 is an example of a loss distribution obtained when the duty ratio of the pulsed light L1 is 50%, and the loss distribution XD2 is a loss obtained when the duty ratio of the pulsed light L1 is 30%. It is an example of distribution. In FIG. 3, the horizontal axis represents the distance (distance from the optical fiber measuring device 1) L in the length direction of the optical fiber 30, and the vertical axis represents the magnitude of loss X.

  In the example shown in FIG. 3, the peak of the loss distribution appears in the portions denoted by reference signs P11 and P12, and even when the duty ratio of the pulsed light L1 is 30%, it is the case where it is 50%. It can also be seen that the positions where each peak appears are the same, and that the peak value (maximum value) at each peak is also the same. For example, for the peak P11, the loss change amount is ΔX regardless of whether the duty ratio of the pulsed light L1 is 30% or 50%. However, the peak values are the same when the distance of the region where the loss is measured compared to the response distance (for example, the region where the peak P11 appears) is sufficiently large, and the loss is measured compared to the response distance. In the reverse case where the distance of the region is sufficiently small, the loss cannot be measured accurately and the peak value becomes different.

  Here, paying attention to the peak P11, the distance at which the magnitude of the loss becomes X1 which is 10% of the change amount ΔX at the rise of the loss distribution XD1 is L11, and the loss is X2 which is 90% of the change amount ΔX. The distance is L12. Therefore, the response distance of the loss distribution XD1 is LR1 = L12−L11. On the other hand, when the loss distribution XD2 rises, the distance at which the loss becomes X1, which is 10% of the variation ΔX, is L13, and the distance at which the loss becomes X2, which is 90% of the variation ΔX, is L14. . Therefore, the response distance of the loss distribution XD2 is LR2 = L14−L13.

  Referring to FIG. 3, the loss distribution obtained when the duty ratio of the pulsed light L1 is set to 30% rather than the response distance LR1 of the loss distribution XD1 obtained when the duty ratio of the pulsed light L1 is set to 50%. It can be seen that the response distance LR2 of XD2 is shorter. Thereby, when the duty ratio of the pulsed light L1 is set to 30%, the response distance becomes shorter and an accurate loss distribution is obtained, and the position of the peak P11 is specified more accurately. It becomes possible to do.

  In this embodiment, the laser light L1 output from the laser light source 11 is adjusted in the duty ratio by the duty ratio adjuster 21, but the frequency for generating the pulsed light L1 is not changed. The same frequency as The frequency of the timing signal TM2 output from the timing processor 20 is also the same as the conventional frequency, and the operating frequencies of the A / D converter 17, the averaging unit 18, and the signal processor 19 are the same as the conventional frequency. For this reason, in this embodiment, it is not necessary to use an expensive A / D converter capable of high-speed sampling, and a significant cost increase is not caused. Moreover, since the position of the measurement point in the length direction of the optical fiber 30 does not change, the convenience for the user is not deteriorated.

[Second Embodiment]
FIG. 4 is a block diagram showing a main configuration of an optical fiber measuring device according to the second embodiment of the present invention. In FIG. 4, the same components as those shown in FIG. An optical fiber measurement device 2 shown in FIG. 4 includes a duty ratio adjuster 51 and a PC 53 (control device) instead of the duty ratio adjuster 21 and the PC 40 provided in the optical fiber measurement device 1 shown in FIG. 52 (measuring instrument) is newly added, and the measurement accuracy is improved by stabilizing the duty ratio of the signal input to the laser driver 22.

  Similar to the duty ratio adjuster 21, the duty ratio adjuster 51 adjusts the rising and falling timings of the timing signal TM1 output from the timing processor 20, thereby the pulsed light L1 output from the laser light source 11. The duty ratio is adjusted. However, while the duty ratio adjuster 21 adjusts timing using a threshold value set in advance by the user, the duty ratio adjuster 51 dynamically uses a control signal output from the PC 53. The difference is that the timing is adjusted.

  The duty ratio measuring instrument 52 measures the duty ratio of the signal output from the duty ratio adjuster 51 to the laser driver 22 (that is, the duty ratio of the pulsed light L1 to be output from the laser light source 11). The duty ratio measuring device 52 can be configured using a low-pass filter corresponding to an integrator and an A / D converter. That is, if a DC (direct current) voltage component is extracted from a signal output from the duty ratio adjuster 51 using a low-pass filter, and the extracted DC voltage component is converted into a digital signal using an A / D converter. A digital signal having a value corresponding to the duty ratio of the signal can be obtained.

  Further, the duty ratio measuring device 52 can also be configured using a sampling device and a counter capable of high-speed sampling. That is, the duty ratio of the signal output from the duty ratio adjuster 51 is measured by sampling the signal output from the duty ratio adjuster 51 at high speed using a sampler and counting the sampling result with a counter. Further, a gate circuit capable of passing a signal output from the duty ratio adjuster 51 at a constant interval can be used instead of the sampling device. If such a gate circuit is used, the duty ratio can be measured if the number of pulses that have passed through the gate circuit is counted at a low speed by a counter, and the cost is not increased.

  PC53 takes in the data output from the output terminal Q2 similarly to PC40 shown in FIG. 1, and displays the loss distribution in the length direction of the optical fiber 30 calculated | required by the signal processor 19. FIG. Further, the PC 53 outputs a control signal to the duty ratio adjuster 51 using the measurement result of the duty ratio measuring instrument 52, and adjusts the duty ratio so that the duty ratio of the signal output from the duty ratio adjuster 51 is constant. The device 51 is subjected to feedback control (feedback control).

  By performing such control, it is possible to make it less susceptible to the influence of ambient temperature fluctuations and external noise. Thereby, the duty ratio of the pulsed light L1 output from the laser light source 11 can be stabilized, and thus the measurement accuracy can be improved. The operations other than the above-described duty ratio adjuster 51, duty ratio measuring instrument 52, and PC 53 are basically the same as those of the optical fiber measuring apparatus 1 according to the first embodiment shown in FIG. Is omitted. In the above description, the form in which the PC 53 performs the feedback control of the duty ratio adjuster 51 has been described. However, a configuration for realizing this feedback control is provided in the optical fiber measuring device 2, and the feedback of the duty ratio adjuster 51 is provided by this configuration. It is also possible to perform the control.

[Third Embodiment]
FIG. 5 is a block diagram showing a main configuration of an optical fiber measuring device according to the third embodiment of the present invention. In FIG. 5, the same components as those shown in FIG. 4 are denoted by the same reference numerals. The optical fiber measurement device 3 shown in FIG. 5 adds a code modulator 60 to the optical fiber measurement device 3 shown in FIG. 4 and replaces the signal processor 19 with a signal processor 61 (correlation processing unit). And improve the response distance and improve the S / N ratio.

  The code modulator 60 performs predetermined code modulation on the timing signal TM <b> 1 output from the timing processor 20, and outputs a code string including a plurality of codes that are not a single pulse to the duty ratio adjuster 51. The code modulator 60 code-modulates the timing signal TM1 using a complementary code such as a Barker code. Here, when the code sequence generated by the code modulator 60 is an NRZ (Non Return to Zero) code, the duty ratio adjusters 21 and 51 (predetermined values) described in the first and second embodiments are used. The duty ratio cannot be adjusted by using a simple duty ratio adjuster that adjusts the duty ratio by using the threshold value, and a complicated and expensive duty time adjuster is required. Therefore, if an RZ (Return to Zero) code is used as a code string generated by the code modulator 60, the duty ratio adjusters 21 and 51 can be used, and the response distance and The SN ratio can be improved.

  FIG. 6 is a timing chart for explaining processing performed by the duty ratio adjuster 51 to which a code string is input. In FIG. 6, a waveform WF11 is an example of a waveform of a signal (code string) output from the code modulator 60, and waveforms WF12 and WF13 are examples of a waveform of a signal output from the duty ratio adjuster 51. In FIG. 6, the time t is plotted on the horizontal axis and the voltage V is plotted on the vertical axis, as in FIG. Here, the waveform WF12 is a waveform of a signal output from the duty ratio adjuster 51 when the duty ratio of the pulsed light L1 emitted from the laser light source 11 is 50%, and the waveform WF13 is emitted from the laser light source 11. This is a waveform of a signal output from the duty ratio adjuster 21 when the duty ratio of the pulsed light L1 is 34%.

  The signal output from the code modulator 60 has, for example, a period of 20 nsec, and has a substantially rectangular waveform having a maximum voltage when the code is “1” and a minimum voltage when the code is “0”, as shown in FIG. In the example shown in FIG. 6, the waveform WF11 of the signal subjected to code modulation of “1”, “1”, “0”, “1”, “0”,. Further, threshold values TH3 and TH4 are set for this signal. The threshold TH3 is a threshold set by the duty ratio adjuster 51 when the duty ratio of the pulsed light L1 is 50%, and the threshold TH4 is the duty ratio adjuster 51 when the duty ratio of the pulsed light L1 is 34%. Is the threshold value set in. These threshold values are not set in advance by the user, but are dynamically set by the PC 53.

  The duty ratio adjuster 51 outputs a signal when the voltage of the signal output from the code modulator 60 increases beyond the threshold, and stops the signal when the voltage of the signal decreases beyond the threshold. To do. Specifically, when the threshold value TH3 is set, the signal is output at time t31 when the voltage of the signal output from the code modulator 60 exceeds the threshold value TH3, and the voltage of the signal is the threshold value TH3. The signal is stopped at time t32 when the value becomes smaller than. Thereby, the waveform WF12 in FIG. 6 having a pulse width of 10 nsec is obtained. Similarly, when the threshold value TH4 is set, a signal is output at time t41 when the voltage of the signal output from the code modulator 60 exceeds the threshold value TH4, and the voltage of the signal exceeds the threshold value TH4. The signal is stopped at the time t42 when the time becomes smaller. Thereby, the waveform WF13 in FIG. 6 having a pulse width of 6.8 nsec is obtained.

  The signal processor 61 operates in synchronization with the timing signal TM2 from the timing processor 20 in the same manner as the signal processor 19 shown in FIG. 1 and the like, and converts the received light data that has been averaged by the averager 18 into the received light data. On the other hand, level correction processing and other arithmetic processing are performed. Here, since the pulsed light L1 emitted from the laser light source 11 is code-modulated, the signal processor 61 performs correlation processing in addition to the above level correction processing and the like. As the correlation processing performed by the signal processor 61, for example, the correlation processing similar to that of Non-Patent Document 1 described above can be used. Here, the case where the correlation processing is performed by the signal processor 61 on the data subjected to the averaging processing by the averaging device 18 will be described as an example. However, the averaging processing and the correlation processing are interchanged to correlate. It is also possible to perform an averaging process on the processed data.

  As described above, in the present embodiment, predetermined code modulation is performed on the timing signal TM1 output from the timing processor 20, and the duty ratio of the signal subjected to the code modulation is adjusted by the duty ratio adjuster 51. ing. For this reason, the response distance can be improved as in the first and second embodiments, and the SN ratio can also be improved. Also in the present embodiment, since the feedback control of the duty ratio adjuster 51 using the measurement result of the duty ratio measuring instrument 52 is performed by the PC 53, it can be made less susceptible to the influence of ambient temperature fluctuations and external noise. . Thereby, the duty ratio of the pulsed light L1 output from the laser light source 11 can be stabilized, and thus the measurement accuracy can be improved.

[Fourth Embodiment]
FIG. 7 is a block diagram showing a main configuration of an optical fiber measurement device according to the fourth embodiment of the present invention. In FIG. 7, the same components as those shown in FIG. The optical fiber measuring device 4 shown in FIG. 7 is provided with a wavelength separator 70 instead of the wavelength separator 14 shown in FIG. 5 and a photodetector instead of the photodetector 15 to the averager 18 and the signal processor 61. 71a and 71b, amplifiers 72a and 72b, A / D converters 73a and 73b, averagers 74a and 74b, and a signal processor 75 (correlation processing unit), in the length direction of the optical fiber 30 It measures the temperature distribution.

  The wavelength separator 70 individually separates the Stokes light L3 and the anti-Stokes light L4 included in the return light L2 from the optical fiber 30 input via the optical fiber connection terminal Q1, and emits light in an unnecessary wavelength range. Remove. The photodetectors 71a to 74a are respectively the same as the photodetectors 15 to 18 shown in FIG. 5, and photoelectrically convert the Stokes light L3 separated by the wavelength separator 70 into a received light signal S11. Then, after the light reception signal S11 is amplified and converted into light reception data, averaging is performed. The photodetectors 71b to 74b are also the same as the photodetectors 15 to 18 shown in FIG. 5, respectively, and the anti-Stokes light L4 separated by the wavelength separator 70 is converted into a received light signal S12. After conversion, the light reception signal S12 is amplified and converted into light reception data, and then averaged.

  The signal processor 75 performs processing such as level correction processing and correlation processing on the light reception data averaged by the averagers 74a and 74b, and also includes light reception data related to the Stokes light L3 and light reception data related to the anti-Stokes light L4. The temperature is calculated by calculating the intensity ratio of The temperature distribution in the length direction of the optical fiber 30 is obtained by arranging the obtained temperatures in the order of sampling of the A / D converters 73a and 73b. The operations other than the wavelength separator 70 to the signal processor 75 (for example, the operation of adjusting the duty ratio of the pulsed light L1) are the same as those of the optical fiber measuring apparatus 3 shown in FIG. Omitted. Also in this embodiment, as in the third embodiment, the averaging process performed by the averagers 74a and 74b and the correlation process performed by the signal processor 75 can be interchanged.

  FIG. 8 is a diagram illustrating an example of a temperature distribution measurement result. In FIG. 8, the temperature distribution TD1 is an example of the temperature distribution obtained when the duty ratio of the pulsed light L1 is 50%, and the temperature distribution TD2 is the temperature obtained when the duty ratio of the pulsed light L1 is 30%. It is an example of distribution. In FIG. 8, the horizontal axis indicates the distance (distance from the optical fiber measuring device 4) L in the length direction of the optical fiber 30, and the vertical axis indicates the temperature T.

  In the example shown in FIG. 8, a temperature distribution is obtained in which the temperature is high in the portion denoted by reference numeral P21 and the temperature is decreased in the portion denoted by reference numeral P22. Referring to FIG. 8, even when the duty ratio of the pulsed light L1 is 30% or 50%, the position where the temperature rises and the part where the temperature rises are the same. Moreover, it can be seen that the local maximum value and the local minimum value are also the same. This is the same as the loss distribution shown in FIG.

  Taking the portion P21 where the temperature becomes high as an example, the amount of change in temperature is ΔT regardless of whether the duty ratio of the pulsed light L1 is 30% or 50%. However, as in the case of the loss distribution, this is for the case where the distance of the region where the temperature change is measured (for example, the portion P21 where the temperature rises) is sufficiently large compared to the response distance, and compared to the response distance In the opposite case where the distance of the region where the temperature change is measured is sufficiently small, the temperature change cannot be measured accurately, and the amount of change in temperature becomes a different value.

  Here, paying attention to the portion P21 where the temperature rises, the distance at which the temperature becomes T1 which is 10% of the change amount ΔT at the rise of the temperature distribution TD1 is L21, and the temperature is T2 which is 90% of the change amount ΔT. Is a distance L22. Therefore, the response distance of the temperature distribution TD1 is LR3 = L22−L21. On the other hand, the distance at which the temperature reaches T1 which is 10% of the change amount ΔT at the rising edge of the temperature distribution TD2 is L23, and the distance at which the temperature becomes T2 which is 90% of the change amount ΔT is L24. Therefore, the response distance of the temperature distribution TD2 is LR4 = L24−L23.

  Referring to FIG. 8, the temperature distribution obtained when the duty ratio of the pulsed light L1 is set to 30% rather than the response distance LR3 of the temperature distribution TD1 obtained when the duty ratio of the pulsed light L1 is set to 50%. It can be seen that the response distance LR4 of TD2 is shorter. Thereby, when the duty ratio of the pulsed light L1 is set to 30%, the response distance is shortened and an accurate temperature distribution is obtained, and the position where the temperature change appears is more accurately set. It becomes possible to specify.

  Also in the present embodiment, the laser light L1 output from the laser light source 11 is adjusted in duty ratio by the duty ratio adjuster 51, but the frequency for generating the pulsed light L1 is not changed. The same frequency as the conventional frequency. The frequency of the timing signal TM2 output from the timing processor 20 is also the same as the conventional frequency, and the operating frequencies of the A / D converters 73a and 73b, the averagers 74a and 74b, and the signal processor 75 are the same as the conventional frequency. The same. For this reason, even in this embodiment, it is not necessary to use an expensive A / D converter capable of high-speed sampling, and a significant cost increase is not caused. Moreover, since the position of the measurement point in the length direction of the optical fiber 30 does not change, the convenience for the user is not deteriorated.

  As mentioned above, although the optical fiber measuring device by embodiment of this invention was demonstrated, this invention is not restrict | limited to the said embodiment, It can change freely within the scope of the present invention. For example, the code modulator 60 and the signal processor 61 of the optical fiber measurement device 3 described in the third embodiment can be applied to the optical fiber measurement device 1 of the first embodiment. Further, the wavelength separator 70 to the signal processor 75 of the optical fiber measuring device 4 described in the fourth embodiment are replaced with the wavelength separator 14 to the signal processor 19 of the optical fiber measuring device 1 of the first and second embodiments. It can be applied instead. However, since the encoding of the pulsed light L1 is not performed, the correlation processing may be omitted for the signal processor 75.

  In the above embodiment, the loss distribution is measured using the backscattered light or the temperature distribution is measured using the back Raman scattered light as an example. The present invention can be applied to various optical fiber measuring apparatuses that measure backscattered light including back Raman scattered light and back Brillouin scattered light and measure various physical quantities such as loss, temperature, and strain.

It is a block diagram which shows the principal part structure of the optical fiber measuring device by 1st Embodiment of this invention. 3 is a timing chart for explaining processing performed by a duty ratio adjuster 21. It is a figure which shows an example of the measurement result of loss distribution. It is a block diagram which shows the principal part structure of the optical fiber measuring device by 2nd Embodiment of this invention. It is a block diagram which shows the principal part structure of the optical fiber measuring device by 3rd Embodiment of this invention. It is a timing chart for demonstrating the process performed with the duty ratio adjuster 51 to which the code sequence was input. It is a block diagram which shows the principal part structure of the optical fiber measuring device by 4th Embodiment of this invention. It is a figure which shows an example of the measurement result of temperature distribution.

Explanation of symbols

1-4 Optical Fiber Measuring Device 11 Laser Light Source 15 Photodetector 20 Timing Processor 21 Duty Ratio Adjuster 30 Optical Fiber 51 Duty Ratio Adjuster 52 Duty Ratio Measuring Instrument 53 PC
60 Code modulator 61, 75 Signal processor 71a, 71b Photodetector L1 Pulse light L2 Return light S1 Light reception signal TM1 Timing signal

Claims (6)

A light source that outputs pulsed light to be incident on the optical fiber, and a light receiver that receives backscattered light obtained by making the pulsed light output from the light source incident on the optical fiber, and is output from the light receiver. In an optical fiber measuring device that measures a predetermined physical quantity in the length direction of the optical fiber based on a received light signal,
An optical fiber measuring apparatus comprising an adjuster for adjusting a duty ratio of pulsed light output from the light source. A timing processor that outputs a timing signal that defines the rising and falling timing of the pulsed light output from the light source;
The optical fiber measuring device according to claim 1, wherein the adjuster adjusts the rising and falling timings of the timing signal output from the timing processor using a predetermined threshold value.   The optical fiber measurement device according to claim 2, wherein the predetermined threshold value used in the adjuster can be set to a different value according to a duty ratio of pulsed light to be incident on the optical fiber. A measuring instrument that measures a duty ratio of pulsed light to be output from the light source using a timing signal via the adjuster;
The optical fiber measuring device according to claim 2, further comprising: a control device that feedback-controls the adjuster according to a measurement result of the measuring device. A code modulator that performs predetermined code modulation on the timing signal output from the timing processor and outputs the code signal to the adjuster;
The optical fiber measurement according to claim 2, further comprising: a correlation processing unit that performs demodulation by performing correlation processing on the light reception signal output from the light receiver. apparatus.   6. The optical fiber measuring device according to claim 5, wherein the code modulator performs code modulation for converting the timing signal output from the timing processor into an RZ signal composed of a predetermined code string.

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