JP2010048706A - Optical fiber vibration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Sagnac interference-type optical fiber vibration sensor which cannot only detect vibration, but which also can obtain positional information on the location where the vibration is occurring. <P>SOLUTION: The Sagnac interference-type optical fiber vibration sensor 1, including optical fiber loops 2a, 2b which are arranged along a structure 4, such as a fence, generating the vibration to be detected, and a vibration sensor body 3 which detects the vibration generated by the structure 4 via the optical fiber loops 2a, 2b, is such that the plural optical fiber loops 2a, 2b which are arranged along the structure 4 are configured to have length values that differ from one another. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a Sagnac interference type optical fiber vibration sensor used for an intrusion detection sensor or the like.

  In order to prevent theft and destruction by intruders, information leakage, or to ensure personal safety, there is an increasing interest in physical security technology. In particular, in important facilities such as airports, harbors, and power plants, measures have been taken to prevent illegal intrusions by setting up fences at the site boundaries. An intrusion detection sensor for detecting an action is required.

  As such an intrusion detection sensor, a vibration sensor that is fixed to a structure such as a fence and detects the vibration of the structure is attracting attention, and it can be expected to reduce costs and durability in the field. The Sagnac interference type optical fiber vibration sensor using the optical fiber has been attracting attention.

  As shown in FIG. 5, in the conventional Sagnac interference type optical fiber vibration sensor 51, a part of the optical fiber loop 52 is used as a sensor detection unit for vibration detection, and the optical fiber loop 52 is used as a structure such as a fence. Arranged along.

In the optical fiber vibration sensor 51, the light emitted from the light source 53 propagates through the first optical coupler 54, is linearly polarized by the polarizer 55, and is branched into two by the second optical coupler 56. The light enters the different ends of the fiber loop 52. Of the light incident on the optical fiber loop 52, one right-handed light L _cw, and the other left-handed light L _ccw.

The left and right light L _cw and L _ccw are modulated in phase by the phase modulator 57, _travel around the optical fiber loop 52, and enter the second optical coupler 56 again. Right and left-handed light L _cw incident on the second optical coupler 56, L _ccw is to interfere with the second optical coupler 56 become interference light propagates through polarizer 55, two again in the first optical coupler 54 The light is branched and one of the branched lights is received by the light receiver 58.

When the optical fiber loop 52 is not vibrating is light receiver 58 is always detecting the constant light intensity, the optical fiber loop 52 is vibrated, the right and left-handed light L _cw, phase difference L _ccw occurs, The light intensity detected by the light receiver 58 changes. By detecting the change in the light intensity by the signal processing unit 59, the vibration of the optical fiber loop 52 is detected.

  The optical fiber vibration sensor 51 can detect the vibration given to the structure by the intruder by detecting the vibration of the optical fiber loop 52 (see, for example, Patent Document 1).

JP 2006-208080 A

  However, although the optical fiber vibration sensor 51 of FIG. 5 can detect the vibration of the structure through the vibration of the optical fiber loop 52, it is possible to specify at which position of the optical fiber loop 52 the vibration has occurred. For example, the position of the intruder (intrusion position information) could not be specified.

  However, in recent years, there has been a need to not only detect an intruder but also specify intrusion position information indicating where the intruder has entered, using a Sagnac interference type optical fiber vibration sensor.

  The present invention has been made in view of the above circumstances, and a Sagnac interference type optical fiber vibration sensor capable of not only detecting vibration but also obtaining position information on where the vibration is occurring is provided. The purpose is to provide.

  The present invention has been devised to achieve the above object, and the invention of claim 1 is generated by an optical fiber loop disposed along a structure such as a fence for detecting vibration and the structure. In a Sagnac interference type optical fiber vibration sensor comprising a vibration sensor main body for detecting vibration through the optical fiber loop, an optical fiber in which a plurality of the optical fiber loops having different lengths are arranged along the structure. It is a vibration sensor.

  The invention of claim 2 divides the structure in the length direction thereof to form a plurality of inspection object regions, and the optical fiber loop arranged along the structure has the number of the inspection object regions. 2. The optical fiber vibration sensor according to claim 1, wherein the number is the same, and the lengths are sequentially different for each of the inspection target regions.

  According to a third aspect of the present invention, each optical fiber loop is connected to the vibration sensor main body, and the vibration sensor main body detects the vibration intensity of each optical fiber loop, and the detected vibration intensity of each optical fiber loop. The optical fiber vibration sensor according to claim 2, wherein the inspection target area where vibration has occurred is identified.

According to a fourth aspect of the present invention, the structure is partitioned in the length direction to form the inspection target regions of length L ₁ , L ₂ ,..., L _n , and the number of the optical fiber loops is n. The length l of each optical fiber loop is expressed by the following equation (1)

The optical fiber vibration sensor according to claim 2 or 3, wherein

  According to a fifth aspect of the present invention, the structure body is partitioned in the length direction to form n inspection target regions having a length L, the number of the optical fiber loops is n, and each optical fiber loop is L × 4. The optical fiber vibration sensor according to claim 2, wherein the optical fiber vibration sensor is formed in a length of i (i = 1, 2,..., n).

  According to the present invention, it is possible not only to detect vibration but also to obtain positional information indicating where the vibration is generated.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  The optical fiber vibration sensor of the present invention is a Sagnac interference type optical fiber vibration sensor, and is used, for example, as an intrusion detection sensor.

  FIG. 1 is a perspective view of an optical fiber vibration sensor according to this embodiment.

  As shown in FIG. 1, the optical fiber vibration sensor 1 includes a plurality of (two in FIG. 1) optical fiber loops 2a and 2b arranged along a structure 4 such as a fence for detecting vibration. And a vibration sensor main body 3 that detects vibration generated in the structure 4 via the optical fiber loops 2a and 2b.

  The optical fiber loop 2a is obtained by making an optical fiber into a loop shape, and the length of the optical fiber constituting the optical fiber loop 2a is approximately twice the length of the optical fiber loop 2a (reciprocal). The same applies to the optical fiber loop 2b.

  The optical fiber loops 2a and 2b are provided substantially in parallel along the structure 4, and the optical fiber loops 2a and 2b are connected to the vibration sensor main body 3, respectively.

  In the present embodiment, the structure 4 is partitioned in the length direction to form two inspection target areas A and B. The inspection target areas A and B are conceptual areas and are not uniformly determined as set values of the optical fiber vibration sensor 1. In short, the detection target areas A and B change depending on the arrangement state of the optical fiber loops 2a and 2b (the shape of the structure 4).

  The lengths of the inspection target areas A and B (lengths along the optical fiber loops 2a and 2b) can be arbitrarily set according to the length and shape of the structure 4, the required position resolution function, etc. m to several km.

  The optical fiber loops 2a and 2b are sequentially formed to have different lengths for each of the inspection target areas A and B. Specifically, the optical fiber loop 2a is a length obtained by adding the length of the inspection target region A and the length of the inspection target region B (the optical fiber constituting the optical fiber loop 2a is approximately twice as long). The optical fiber loop 2b is formed to have the same length as the inspection target region A (the optical fiber constituting the optical fiber loop 2b is approximately twice as long).

  That is, the optical fiber loop 2a is disposed over the entire length of the inspection target region A and the inspection target region B, and the optical fiber loop 2b is disposed over the entire length of the inspection target region A. As a result, the optical fiber loops 2a and 2b exist in the inspection target region A, and only the optical fiber loop 2a exists in the inspection target region B.

  When the vibration sensor main body 3 and the structure 4 are provided apart from each other, each optical fiber loop 2a, 2b is formed to have a length obtained by adding the length between the vibration sensor main body 3 and the structure 4 to the length described above. Good.

  As the optical fiber loops 2a and 2b, polarization maintaining optical fibers (PMF) may be used. This is because when a single mode fiber (SMF) is used as the optical fiber loops 2a and 2b, the SMF propagates two inherent polarization modes having slightly different propagation constants. This is because mode conversion occurs due to a disturbance such as a temperature change, and interference noise is generated due to this mode conversion.

  As shown in FIG. 2, the vibration sensor main body 3 includes a light source 21, a light receiver 22 such as a photodiode, a first optical coupler 23, a polarizer 24, and a second light corresponding to the optical fiber loops 2 a and 2 b. A coupler 25, a phase modulator 26, and connection optical fibers 27a, 27b, and 27c for optically connecting them, and a signal processing unit 28 that is shared by the optical fiber loops 2a and 2b and a housing for housing them. 29.

  For example, an SLD (super luminescent diode) may be used as the light source 21. As a result, it is possible to reduce interference noise generated by interference between return light from the optical fiber loops 2a and 2b and Rayleigh scattered light.

  Connection optical fibers 27a and 27b are connected to the light source 21 and the light receiver 22, respectively. Both the connection optical fibers 27a and 27b are connected to a first optical coupler 23 that is an optical branching and coupling element. The optical couplers 23 and 25 are optical fiber couplers having 1 × 2 input / output ports. The first optical coupler 23 is connected to the connection optical fiber 27 c, and the connection optical fiber 27 c is connected to one input / output port of the second optical coupler 25. Both ends of the optical fiber loop 2a (or 2b) are connected to the two input / output ports of the second optical coupler 25, respectively.

  A polarizer 24 is formed in the connecting optical fiber 27 c between the first optical coupler 23 and the second optical coupler 25. The polarizer 24 is a fiber-type polarizer in which a part of the connecting optical fiber 27c is formed in a coil shape and the core birefringence is increased. The polarizer 24 is for making light from the light source 21 into linearly polarized light.

  A phase modulator 26 is provided on one end side of the optical fiber loops 2a and 2b. The phase modulator 26 applies phase modulation with a relative time delay to the light propagating through the optical fiber loops 2a and 2b in opposite directions.

  The intensity of the light detected by the light receiver 22 is proportional to the sine of the phase difference of the light propagating through the optical fiber loop 2a (or 2b) in the opposite direction. Therefore, the sensitivity to a phase difference near zero, that is, a slight vibration. Is low. Therefore, by performing phase modulation by the phase modulator 26 to increase the phase difference, sensitivity to minute vibrations can be improved.

  In the present embodiment, a phase modulator 26 in which a part of the optical fiber loop 2a (or 2b) is wound around a cylindrical PZT (piezoceramic) serving as a vibrator is used. The phase modulator 26 can modulate the phase of light propagating through the optical fiber loops 2a and 2b by expanding and contracting the optical fiber loops 2a and 2b wound around the PZT with a voltage applied to the PZT.

  As the connection optical fibers 27a, 27b, and 27c, polarization plane preserving optical fibers may be used similarly to the optical fiber loops 2a and 2b.

  The signal processing unit 28 drives the light source 21, processes an electrical signal obtained by photoelectric conversion of the optical signal detected by the receiver 22, controls the modulation level of the phase modulator 26, and processing results (vibration waveform, vibration intensity, etc.) ). The signal processing unit 28 is electrically connected to the light source 21, the receiver 22, and the phase modulator 26.

  The signal processing unit 28 detects the vibration intensity of each optical fiber loop 2a, 2b based on the electrical signal from the receiver 22, and compares the detected vibration intensity of each optical fiber loop 2a, 2b. And the area | region identification means which pinpoints the test | inspection area | region where the vibration generate | occur | produced is provided.

  Next, the operation of the optical fiber vibration sensor 1 according to this embodiment will be described.

  The light emitted from the light source 21 propagates through the first optical coupler 23, is linearly polarized by the polarizer 24, and enters the second optical coupler 25. In the second optical coupler 25, the incident light is branched into two, and the branched light is incident on different ends of the optical fiber loops 2a and 2b, respectively.

  The left and right light propagating through the optical fiber loops 2 a and 2 b is phase-modulated by the phase modulator 26, goes around the optical fiber loops 2 a and 2 b, and enters the second optical coupler 25 again. The left-right light that has entered the second optical coupler 25 interferes with the second optical coupler 25 and becomes interference light. This interference light propagates through the polarizer 24 and is branched again into two lights by the first optical coupler 23, and one of the branched lights is received by the light receiver 22.

  When the optical fiber loops 2a and 2b are not oscillating, the light receiver 22 always detects a constant light intensity. However, when the optical fiber loops 2a and 2b oscillate, the right and left waves propagate through the optical fiber loops 2a and 2b. A phase difference occurs in the circulating light, and the light intensity detected by the light receiver 22 changes. Since the light intensity received by the light receiver 22 is proportional to the sine of the phase difference between the left and right light, the greater the vibration applied to the optical fiber loops 2a and 2b, the larger the phase difference, and the light received by the light receiver 22. The change in intensity also increases.

  The signal processing unit 28 detects vibrations of the optical fiber loops 2a and 2b by detecting a change in light intensity received by the light receiver 22 based on an electrical signal from the light receiver 22, and also detects the optical fiber loops 2a and 2b. The intensity of vibration given to 2b can also be obtained.

  Here, a case where vibration occurs in each of the inspection target areas A and B will be described.

  When vibration occurs in the inspection target area A, since the optical fiber loops 2a and 2b exist in the inspection target area A, both the optical fiber loops 2a and 2b vibrate with substantially the same intensity.

  FIGS. 3A and 3B show examples of vibration waveforms obtained from both the optical fiber loops 2a and 2b when vibration occurs in the inspection target region A. FIG. FIG. 3A shows a vibration waveform obtained from the optical fiber loop 2a, and FIG. 3B shows a vibration waveform obtained from the optical fiber loop 2b.

As shown in FIGS. 3A and 3B, when vibration occurs in the inspection target region A, both optical fiber loops 2a and 2b vibrate with substantially the same intensity. The vibration waveforms obtained are substantially the same, and the vibration intensity obtained by the signal processing unit 28 is substantially the same. When vibration occurs in the inspection target region A, the time t _{1 when the} vibration is detected by the optical fiber loop 2a and the time t ₁ ′ when the vibration is detected by the optical fiber loop 2b are substantially the same. That is, vibrations are detected almost simultaneously in both optical fiber loops 2a and 2b.

  On the other hand, when vibration occurs in the inspection target region B, since only the optical fiber loop 2a exists in the inspection target region B, the vibration strength of the optical fiber loop 2a increases, and the vibration strength of the optical fiber loop 2b increases. Becomes smaller.

  An example of the vibration waveform obtained by the signal processing unit 28 at this time is shown in FIGS. 4 (a) and 4 (b). FIG. 4A shows a vibration waveform obtained from the optical fiber loop 2a, and FIG. 4B shows a vibration waveform obtained from the optical fiber loop 2b.

As shown in FIGS. 4A and 4B, when vibration occurs in the inspection target region B, the vibration waveform obtained from the optical fiber loop 2a is different from the vibration waveform obtained from the optical fiber loop 2b. The vibration intensity obtained by the signal processing unit 28 is larger than the vibration intensity obtained from the optical fiber loop 2b. Incidentally, when the vibration occurs in the inspection region B, because of the time taken vibration is transmitted to the optical fiber loop 2b, the detected time t ₂ vibrations by an optical fiber loop 2a, detects vibrations through the optical fiber loop 2b A time difference (delay) occurs between the measured time t ₂ ′.

  That is, if the vibration intensity obtained from both optical fiber loops 2a and 2b is the same, vibration has occurred in the inspection target area A, and the vibration intensity obtained from the optical fiber loop 2a is equal to the optical fiber loop. If it is greater than the intensity of vibration obtained from 2b, it means that vibration has occurred in the inspection area B.

  As described above, the vibration intensity obtained from the optical fiber loops 2a and 2b differs between the case where the vibration occurs in the inspection target region A and the case where the vibration occurs in the inspection target region B.

  When the region specifying means of the signal processing unit 28 detects vibration at the time of the optical fiber loop 2a (or 2b), the intensity of the vibration detected by the optical fiber loop 2a (or 2b) and the same time as this The vibration intensity of the other optical fiber loop 2b (or 2a) is compared.

  The region specifying means of the signal processing unit 28 specifies in which inspection target region the vibration is generated by comparing the intensity of vibration obtained in each of the optical fiber loops 2a and 2b. The signal processing unit 28 outputs information on the inspection target area where the vibration specified by the area specifying means has occurred, for example, to a monitoring device connected to the outside.

  Thereby, the position (position information) where the vibration is generated can be obtained, and the position information indicating where the vibration is generated in the structure 4 can be obtained.

  Further, when the lengths of the inspection target areas A and B are increased to, for example, 10 m or longer, it takes time for the vibration generated in the inspection target area B to be transmitted to the inspection target area A, and vibration in the optical fiber loop 2b May be detected late. In this case, it is preferable to compare the vibration intensity of the optical fiber loop 2a detected first with the vibration intensity of the optical fiber loop 2b detected after detecting the vibration of the optical fiber loop 2a.

  Further, in the inspection target area other than the inspection target area A closest to the vibration sensor main body 3 (in this embodiment, the inspection target area B), it is also possible to estimate at which position in the inspection target area the vibration has occurred. It is.

  As an example, a case where vibration occurs in the inspection target region B will be described. When vibration occurs near the inspection target region A in the inspection target region B, the intensity of vibration obtained from the optical fiber loop 2b increases. When vibration occurs at a position away from the inspection target area A in the inspection target area B, the intensity of vibration obtained from the optical fiber loop 2b decreases. Therefore, by obtaining the relationship between the vibration intensity ratio obtained from the optical fiber loop 2a and the vibration intensity ratio obtained from the optical fiber loop 2b in advance and the position where the vibration in the inspection object area B occurs, the inspection object area is obtained. It is also possible to estimate at which position in B the vibration has occurred. Furthermore, by considering the time difference at which vibration is detected in each of the optical fiber loops 2a and 2b, it is possible to estimate more accurately at which position in the inspection target region B the vibration has occurred.

  The signal processing unit 28 may perform Fourier transform on the vibration waveform obtained from each of the optical fiber loops 2a and 2b, and analyze the cause of vibration from the frequency characteristics. As a result, it is possible to estimate whether the vibration is due to a natural phenomenon such as rain or wind or due to human factors.

  As described above, in the optical fiber vibration sensor 1 according to the present embodiment, a plurality of optical fiber loops 2a and 2b having different lengths are arranged along a structure 4 such as a fence.

  Thus, if the intensity of vibration obtained from each optical fiber loop 2a, 2b is compared, whether vibration has occurred at the position where both optical fiber loops 2a, 2b are arranged, or one of the optical fiber loops 2a (or 2b). ) Can be specified at the position where only the vibration is arranged, and the position information on the position where the vibration has occurred in the structure 4 can be obtained. By obtaining the position information where the vibration has occurred, for example, the intrusion position information where the intruder has entered can be obtained.

  Further, in the optical fiber vibration sensor 1, the structure 4 is partitioned in the length direction to form a plurality of inspection target areas A and B, and the optical fiber loops 2a and 2b have the same number as the number of inspection target areas. In addition, the inspection target areas A and B are sequentially formed to have different lengths.

  As a result, since there are different numbers of optical fiber loops 2a and 2b in each of the inspection target areas A and B, if the intensity of vibration obtained from each of the optical fiber loops 2a and 2b is compared, which inspection target It is possible to specify whether vibration has occurred in the region. Since the length of the region to be inspected (the length along the optical fiber loops 2a and 2b) can be designed arbitrarily, the number of surveillance cameras arranged, the length of the structure 4, or the required position resolution It is possible to design with a high degree of freedom according to the situation.

  The embodiment of the present invention is not limited to the above embodiment.

  For example, in the above embodiment, the number of inspection target areas is two. However, the present invention is not limited to this, and the number of inspection target areas may be three or more. In this case, the same number of optical fiber loops as the number of inspection target regions are arranged, and each optical fiber loop is sequentially formed to have a different length for each inspection target region (the number of optical fiber loops existing in the inspection target region is Be different).

  Specifically, when n inspection target areas are formed, n optical fiber loops exist in the inspection target area closest to the vibration sensor main body 3, and as the distance from the vibration sensor main body 3 increases, It is preferable that the number of fibers is sequentially decreased so that one optical fiber loop exists in the inspection target region farthest from the vibration sensor main body 3.

  In this case, the region specifying means of the signal processing unit 28 has the same vibration intensity obtained from all the optical fiber loops in the inspection target region, and vibration is applied to the inspection target region closest to the vibration sensor body 3. The generated inspection target area is specified.

When the structure 4 is partitioned in the length direction to form inspection target regions having lengths L ₁ , L ₂ ,..., L _n , the number of optical fiber loops is n. Is the expression (1) shown in [Equation 2].

Formed.

  When the length of each inspection object region (length along the optical fiber loop) is formed to be equal, assuming that the length of the inspection object region is L, the length of each optical fiber loop is L × i (i = 1, 2,..., N).

  The position resolution function can be improved by increasing the number of regions to be inspected, that is, by increasing the number of optical fiber loops.

  In the above embodiment, the number of optical fiber loops is the same as the number of inspection target regions, but the number of optical fiber loops may be equal to or greater than the number of inspection target regions, for example, two for each inspection target region. An optical fiber loop may be arranged.

  In the above embodiment, the light sources 21 corresponding to the optical fiber loops 2a and 2b are provided. However, a single light source shared by the optical fiber loops 2a and 2b may be provided.

  Furthermore, in the above embodiment, each optical fiber loop 2a, 2b is connected to one vibration sensor body 3, but each optical fiber loop 2a, 2b is connected to another vibration sensor corresponding to each optical fiber loop 2a, 2b. The vibration data (vibration waveform or vibration intensity) output from each vibration sensor main body is input to the analyzer separately provided, and obtained from the optical fiber loops 2a and 2b by the analyzer. You may make it identify in which inspection object area | region the vibration generate | occur | produced by comparing the intensity | strength of a vibration.

  In the above embodiment, the optical fiber loops 2a and 2b are provided substantially parallel along the structure 4. However, the optical fiber loops 2a and 2b may not be substantially parallel if they do not deviate from this technical idea. The fiber loop 2b may be provided at 45 degrees.

It is a perspective view of the optical fiber vibration sensor of this invention. It is a schematic top view of the optical fiber vibration sensor of FIG. 3A and 3B are diagrams showing vibration waveforms obtained from each optical fiber loop when vibration occurs in the inspection target region A in the optical fiber vibration sensor of FIG. 4A and 4B are diagrams showing vibration waveforms obtained from each optical fiber loop when vibration occurs in the inspection target region B in the optical fiber vibration sensor of FIG. It is the schematic of the conventional optical fiber vibration sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber vibration sensor 2a, 2b Optical fiber loop 3 Vibration sensor main body 4 Structure

Claims (5)

A Sagnac interference type optical fiber comprising an optical fiber loop disposed along a structure such as a fence for detecting vibration, and a vibration sensor body for detecting vibration generated in the structure through the optical fiber loop. In the vibration sensor,
A plurality of optical fiber loops having different lengths are disposed along the structure.   The structure is partitioned in the length direction to form a plurality of inspection target areas, and the number of the optical fiber loops arranged along the structure is the same as the number of the inspection target areas. The optical fiber vibration sensor according to claim 1, wherein the optical fiber vibration sensor is sequentially formed to have a different length for each inspection target region.   Each optical fiber loop is connected to the vibration sensor main body, and the vibration sensor main body detects the vibration intensity of each optical fiber loop and compares the detected vibration intensity of each optical fiber loop to detect vibration. The optical fiber vibration sensor according to claim 2, wherein the generated inspection target area is specified. The structure is partitioned in the length direction to form the inspection target regions having lengths L ₁ , L ₂ ,..., L _n , and the number of the optical fiber loops is n. Formula (1) where the length l is shown in [Formula 1]

The optical fiber vibration sensor according to claim 2 or 3, wherein   The structure is partitioned in the longitudinal direction to form n inspection target regions having a length L, the number of the optical fiber loops is n, and each optical fiber loop is L × i (i = 1, 2). ,..., N), the optical fiber vibration sensor according to claim 2 or 3.

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