JP2008020342A - External force detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external force detecting apparatus capable of detecting a working position of an external force on an optical fiber without severely pushing up the cost. <P>SOLUTION: A light source device composed of a light source 11 and a modulator 12 outputs measurement light being intensity-modulated, and the measurement light is input to an optical fiber section 14. An optical receiver 15 receives return light obtained by inputting the measurement light to the optical fiber section 14. The optical fiber section 14 is composed of transmission-use optical fibers 21a-21d, branch optical fibers 23a-23e branching from the transmission-use optical fibers 21a-21d and the like. Sensor modules 24a-24e each having an optical sensor which changes into its light transmitting state or light absorbing state in accordance with existence of working of the external force, and an attenuator for bringing the amplitude of the return light which returns to the optical receiver 15, to be a prescribed value, are disposed on the branch optical fibers 23a-23e. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an external force detection device that detects the presence or absence of an external force applied to an optical fiber.

  In recent years, research and development of optical fiber sensing technology that detects changes in the state of an optical fiber by analyzing the characteristics of scattered light generated inside the optical fiber or transmitted light that reaches the end of the fiber has been actively researched and developed. Has been done. As one type of this technique, there is an external force detection device that detects a position where an external force is applied to an optical fiber. For example, as disclosed in Patent Document 1 below, this external force detection device is an intruder who climbs over a fence installed at a site boundary and enters the site, or an intruder who breaks the fence and enters the site. It can be applied to a crime prevention system that detects

  Conventionally, in a crime prevention system, a sensor such as a mechanical tension sensor, a vibration sensor, an infrared cut-off sensor, and an electric field sensor is often used as an external force detection device. However, since these devices have some difficulty in reliability against lightning and electromagnetic noise when performing wide-area monitoring, in recent years, external force detection devices using optical fiber sensing technology have been used from the viewpoint of improving reliability. As an external force detection device to which optical fiber sensing technology is applied, for example, a device using an FBG (Fiber Bragg Grating) sensor or a device that detects a cut portion of an optical fiber using an OTDR (Optical Time Domain Reflectmeters) device has been proposed. . The FBG sensor is attached to the fence to detect the presence of an external force, and the OTDR device is attached to the fence to detect the presence or absence of destruction.

Here, the FBG sensor is one in which a periodic change in refractive index (Bragg grating) is formed over a certain length in a core portion through which light of an optical fiber passes, and broadband light is incident on the optical fiber. Thus, by detecting a change in the specific wavelength component of the reflected light (a specific wavelength component corresponding to the lattice spacing and refractive index of the FGB), it is detected whether or not the sensor section is distorted. Further, the OTDR device is a device that makes light incident on an optical fiber and monitors a change in intensity of the return light to detect a cut portion of the optical fiber.
JP 2005-32224 A

  Incidentally, the FBG sensor needs to detect a specific wavelength with high accuracy, and the OTDR apparatus needs to detect weak backscattered light with high accuracy. For this reason, the conventional external force detection device to which the optical fiber sensing technology is applied has a problem in that the cost tends to increase.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an external force detection device that can detect the acting position of an external force on an optical fiber without a significant increase in cost.

In order to solve the above-described problems, an external force detection device according to the present invention includes a light source device (11, 12) that outputs measurement light with modulated intensity, and inputs the measurement light to optical transmission lines (21a to 21d). A light-receiving device (15) that receives the return light obtained in this manner, and a determination device (16, 17) that detects the phase of the light-receiving signal from the light-receiving device and determines whether or not an external force acts on the optical transmission line. In the external force detection device (10) provided, at least one branch optical transmission line (23a to 23e) provided to be branched with respect to the optical transmission line, and provided in the middle of the branched optical transmission line, The sensor module includes a sensor module (24a to 24e) that changes the return light according to the presence or absence of an action and sets the amplitude of the return light received by the light receiving device to a predetermined value.
According to the present invention, the measurement light output from the light source device is partly branched into the branched optical transmission line while propagating through the optical transmission line. The measurement light propagating through the branch light transmission path is input to a sensor module provided in the middle of the branch light transmission path, and the return light changes depending on the presence or absence of an external force. The return light from the sensor module has a predetermined amplitude and is received by the light receiving device.
Here, the external force detection device of the present invention includes an optical sensor (26) in which the sensor module switches between a state of transmitting light and a state of absorbing light depending on the presence or absence of an external force, and the branched light transmission. It is desirable to provide an attenuator (27) for setting the amplitude of the return light returning from the path to the light receiving device to a predetermined value.
Further, in the external force detection device of the present invention, each attenuator provided in the branch optical transmission line is set so that the amplitude of the return light returning from each of the branch optical transmission lines to the light receiving device becomes a constant value. It is characterized in that an attenuation amount is set.
Moreover, the external force detection device of the present invention is characterized in that the optical sensor and the attenuator are integrated.
Preferably, in the external force detection device of the present invention, the light source device outputs, as the measurement light, the light source (11) and intensity-modulated light obtained by intensity-modulating the output light of the light source using a predetermined modulated signal. A phase detector (16) for detecting a phase difference between an envelope of the received light signal and an envelope of the modulated signal, and a light modulator (12). And a determination unit (17) for determining the presence or absence of the action of the external force based on the phase detection signal.
In the external force detection device of the present invention, the determination unit determines which of the optical sensors has an external force based on a change in the phase detection signal.
Furthermore, in the external force detection device of the present invention, the branched light transmission path includes a reflection member (25) that reflects the measurement light and generates reflected light at the end thereof, or The terminal is a reflection end that reflects the measurement light and generates reflected light.

  According to the present invention, since it is not necessary to detect a specific wavelength or weak backscattered light with high accuracy, it is possible to detect the position where the external force is applied without significantly increasing the cost.

  Hereinafter, an external force detection device according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of an external force detection device according to an embodiment of the present invention. As shown in FIG. 1, the external force detection device 10 of this embodiment includes a light source 11, a modulator 12, a circulator 13, an optical fiber unit 14, a light receiver 15, a phase detector 16, and a determination unit 17.

  The light source 11 is, for example, an LED (Light Emitting Diode) or an LD (Laser Diode), and emits light having a certain amplitude and wavelength. The modulator 12 intensity-modulates the light emitted from the light source 11 with a modulated signal having a predetermined frequency, and emits the light to the circulator 13 as measurement light. Further, the modulator 12 outputs the modulated signal Sm to the phase detector 16. The modulator 12 may modulate the light emitted from the light source 11 as described above, or directly modulate the light source 11 so as to supply a modulated current to the LED, for example. It may be. In the latter case, the intensity-modulated measurement light is emitted directly from the LED.

  The circulator 13 emits measurement light emitted from the modulator 12 (or measurement light emitted directly from the light source 11) to the optical fiber unit 14 and from the optical fiber unit 14 in a direction opposite to the traveling direction of the measurement light. Returning light (reflected light) returning is emitted to the light receiver 15.

  The optical fiber unit 14 includes a plurality of transmission optical fibers 21a to 21d (optical transmission paths), a plurality of optical couplers 22a to 22d, a plurality of branch optical fibers 23a to 23e (branch optical transmission paths), and a plurality of sensor modules 24a. To 24e. In FIG. 1, for convenience of illustration, the optical fiber portion 14 in a partially bent state is illustrated, but the optical fiber portion 14 may be arranged in a straight line, and the arrangement thereof is arbitrary. is there.

  The optical couplers 22a to 22d have four input / output terminals, and multiplex / demultiplex the input light and output it. One input / output end of the optical coupler 22a is connected to the circulator 13 by a transmission optical fiber 21a. The optical couplers 22a and 22b are connected by the transmission optical fiber 21b, the optical couplers 22b and 22c are connected by the transmission optical fiber 21c, and the optical couplers 22c and 22d are connected by the transmission optical fiber 21d. ing.

  The branch optical fiber 23a is provided with a sensor module 24a at one end, and the other end is connected to the optical coupler 22a. The branch optical fiber 23a is provided with a sensor module 24b at one end, and the other end is connected to the optical coupler 22b. Similarly, the branch optical fiber 23c is provided with a sensor module 24c at one end, and the other end is connected to the optical coupler 22c. Further, the branch optical fibers 23d and 23e are respectively provided with sensor modules 24d and 24e at one end, and the other ends are connected to different input / output ends of the optical coupler 22d. That is, the plurality of branch optical fibers 23a to 23e are in a state of being branched with respect to the transmission optical fibers 21a to 21d.

  Next, the sensor modules 24a to 24e connected to the branch optical fibers 23a to 23e will be described. In addition, since the structure of the sensor modules 24a-24e is the same structure, below, the sensor module 24a is demonstrated and description is abbreviate | omitted about the sensor modules 24b-24e. FIG. 2 is a block diagram showing the configuration of the sensor module 24a. As shown in FIG. 2, the sensor module 24a includes a reflection member 25, an optical sensor 26, and an attenuator 27 provided at the end of the branch optical fiber 23a.

  The reflection member 25 reflects the measurement light that has propagated through the branch optical fiber 23a. When the measurement light is reflected by the reflecting member 25, the measurement light becomes reflected light that travels in the direction opposite to the propagation direction. The reflection member 25 may be a member in which an optical member such as a mirror is attached to the end of the branch optical fiber 23a, or may be the end surface itself (reflection end) of the branch optical fiber 23a. If the end face itself of the branch optical fiber 23a is used as a reflection end, for example, extension of the branch optical fiber 23a can be flexibly dealt with.

  The optical sensor 26 is in a state where the measurement light leaks from the core to the clad and is absorbed by the clad when no external force is applied, and transmits the measurement light and the reflected light that travels inside the branch optical fiber 23a when the external force acts. It becomes a state. That is, in the state where no external force is applied to the optical sensor 26, no reflected light is generated in the sensor module 24a, but when an external force is applied to the optical sensor 26, reflected light is generated in the sensor module 24a.

  The attenuator 27 attenuates the measurement light transmitted through the optical sensor 26 and the reflected light reflected by the reflecting member 25 by a predetermined amount. Here, the attenuator of the attenuator 27 provided in each of the sensor modules 24a to 24e is known. For example, the attenuation amount of the attenuator 27 provided in each of the sensor modules 24a to 24e is set so that the intensity of the reflected light incident on the light receiver 15 among the reflected light generated by the sensor modules 24a to 24e is the same. Has been. The attenuation amount of each attenuator 27 provided in the sensor modules 24a to 24e is preferably set so that the intensity of each reflected light incident on the light receiver 15 is completely the same, but the range of detection error If it is within, a certain amount of error is recognized.

  The light receiver 15 photoelectrically converts the reflected light incident through the circulator 13 and outputs a voltage signal Sr corresponding to the light intensity of the reflected light to the phase detector 16. This voltage signal Sr is an electric signal indicating an envelope of reflected light. As described above, when no external force is applied to each of the optical sensors 26 included in the sensor modules 24a to 24e, the reflected light is not incident on the light receiver 15, so that the phase of the voltage signal Sr output from the light receiver 15 is in an indefinite state. Become. On the other hand, when an external force is applied to one or more of the optical sensors 26 provided in the sensor modules 24a to 24e, the reflected light enters the light receiver 15, and the light receiver 15 has a phase corresponding to the phase of the envelope of the reflected light. Voltage signal Sr is output.

  The phase detector 16 detects the phase difference between the voltage signal Sr input from the light receiver 15 and the modulated signal Sm input from the modulator 12, and outputs the detection signal to the determination unit 17. FIG. 3 is a block diagram showing the internal configuration of the phase detector 16. As shown in FIG. 3, the phase detector 16 has a configuration similar to that of a lock-in amplifier, and includes PSDs (Phase Sensitive Detectors) 31a and 31b, low-pass filters (LPF) 32a and 32b, a phase shifter 34, and A phase detector 33 is provided.

  The PSD 31 a multiplies the voltage signal Sr output from the light receiver 15 and the modulated signal Sm output from the modulator 12. The LPF 32a has a cut-off frequency characteristic whose cut-off frequency is sufficiently lower than the frequency of the voltage signal Sr and the modulated signal Sm, and transmits only the signal X having a component equal to or lower than the cut-off frequency. The phase shifter 34 shifts (shifts) the phase of the modulated signal Sm output from the modulator 12 by 90 degrees.

  The PSD 31b multiplies the voltage signal Sr output from the light receiver 15 and the signal output from the phase shifter 34. Similar to the LPF 32a, the LPF 32b has a cut-off frequency characteristic whose cut-off frequency is sufficiently lower than the frequencies of the voltage signal Sr and the modulated signal Sm, and transmits only the signal Y having a component equal to or lower than the cut-off frequency. Based on the signal X output from the LPF 32a and the signal Y output from the LPF 32b, the phase detection unit 33 generates a voltage signal Sr output from the light receiver 15 and a modulated signal Sm output from the modulator 12. A phase difference is detected, and a detection signal is output to the determination unit 8.

Next, the detection principle of the phase detector 16 will be specifically described. Now, it is assumed that the voltage signal Sr output from the light receiver 15 is sin (ωt + α), and the modulated signal Sm output from the modulator 12 is cos (ωt + β). When these signals are multiplied by the PSD 31a, a signal represented by the following equation (1) is obtained.

When the signal expressed by the above equation (1) is input to the LPF 32a and components having a cutoff frequency that is sufficiently lower than the frequency of the voltage signal Sr and the modulated signal Sm are removed, the signal expressed by the following equation (2) X is obtained.

When the modulated signal Sm output from the modulator 12 is input to the phase shifter 34, the phase shifter 34 outputs a signal (cos (ωt + β)) whose phase is shifted by 90 degrees with respect to the voltage signal Sr. Is done. When the voltage signal Sr output from the light receiver 15 and the signal output from the phase shifter 34 are multiplied by the PSD 31b, a signal represented by the following equation (3) is obtained.

When the signal expressed by the above expression (3) is input to the LPF 32b and components having a cutoff frequency that is sufficiently lower than the frequency of the voltage signal Sr and the modulated signal Sm are removed, the signal expressed by the following expression (4) Y is obtained.

位相検出部３３は、ＬＰＦ３２ａ，３２ｂから出力される信号Ｘ，Ｙから、上記の（５）式を用いて変調器１２から出力される被変調信号Ｓｍと受光器１５から出力される電圧信号Ｓｒとの位相差φ（＝α−β）を求める。 Here, assuming that α−β = φ, the signals X and Y output from the LPFs 32a and 32b are shown in the phase space as shown in FIG. FIG. 4 is a diagram showing the signals X and Y output from the LPFs 32a and 32b in the phase space. Note that R in FIG. 4 is the magnitude of a signal obtained by combining the signals X and Y output from the LPFs 32a and 32b. The magnitude R of this signal and the phase φ of the outputs X and Y of the LPFs 32a and 32b are expressed by the following equation (5).

From the signals X and Y output from the LPFs 32a and 32b, the phase detection unit 33 uses the above equation (5) to output the modulated signal Sm output from the modulator 12 and the voltage signal Sr output from the light receiver 15. To obtain a phase difference φ (= α−β).

  The determination unit 17 determines whether or not an external force is applied to the optical fiber unit 14 based on the detection signal input from the phase detector 16. The determination unit 17 includes an A / D converter that quantizes a detection signal (analog signal) output from the phase detector 16, a storage unit that stores a predetermined determination processing program, and a digital signal output from the A / D converter. The CPU includes a central processing unit (CPU) that performs detection processing based on the above-described determination processing program on detection data as a signal, and an output unit that outputs a determination processing result by the CPU to the outside.

Next, the principle of external force detection by the external force detection device 10 of the present embodiment will be described. The wavelength λ of the modulated signal used by the modulator 12 for intensity modulation is f for the frequency of the modulated signal, c for the speed of light, and the refractive index of the optical fiber section 14 (transmission optical fibers 21a to 21d and branch optical fibers). When the refractive index of 23a to 23e is n, it is represented by the following formula (6).

Further, the distance from the light source 11 to the circulator 13 and the distance from the circulator 13 to the light receiver 15 are the same distance, and the distance from the light source 11 to any of the reflecting members 25 provided in the sensor modules 24a to 24e is L. Then, the distance from the light source 11 to the light receiver 15 is expressed as 2L. The relationship between the distance 2L and the wavelength λ of the modulated signal is expressed by the following equation (7).

上記（８）式中における位相角φは、光源１１から射出された測定光を基準としたときの受光器１５に受光される反射光の包絡線の位相差を示している。 Here, N is a positive integer, and l is a certain length that satisfies the relationship l <λ. When the wavelength λ of the modulated signal is made to correspond to a phase angle of 2π radians, the length l is expressed by the following equation (8) when the length l corresponds to φ radians.

The phase angle φ in the above equation (8) indicates the phase difference of the envelope of the reflected light received by the light receiver 15 when the measurement light emitted from the light source 11 is used as a reference.

  In the present embodiment, as shown in FIG. 1, a plurality of sensor modules 24 a to 24 e are provided, and a plurality of reflected lights may be generated due to an external force acting on a plurality of optical sensors 26 provided on these. For this reason, it is necessary to determine in which sensor module 24a to 24e the reflected light received by the light receiver 15 is generated.

Now, the amplitude (maximum value of the envelope) of the reflected light generated by the sensor modules 24a to 24e and received by the light receiver 15 is P _{A to} P _E , and the phases are φ _A to φ _E , respectively. Then, the reflected light received by the light receiver 15 is expressed by the following equation (9).

The voltage signal Sr output from the light receiver 15 becomes a signal proportional to the amplitude of the reflected light expressed by the above equation (9), and the phases φ _{A to} φ _E in the above equation (9) can be detected. If possible, it is detected in which sensor module 24a-24e the reflected light received by the light receiver 15 is generated, that is, in which optical sensor 26 provided in the sensor module 24a-24e is applied. can do. However, when the amplitudes P _{A to} P _E of the reflected lights are different, the component having a large amplitude becomes dominant, and it becomes difficult to detect other components (components having a small amplitude).

  Now, let us consider a case where the attenuator 27 is not provided in each of the sensor modules 24 a to 24 e and reflected light having different amplitudes enters the light receiver 15. FIG. 5 is a diagram illustrating an example of reflected light having different amplitudes incident on the light receiver 15. In FIG. 5, the horizontal axis represents time and the vertical axis represents amplitude. FIG. 5A is a diagram illustrating an example of a temporal change in the amplitude of the reflected light R1 incident on the light receiver 15 out of the reflected light generated by the sensor module 24a. FIG. 5B is a diagram illustrating an example of a temporal change in the amplitude of the reflected light R2 incident on the light receiver 15 out of the reflected light generated by the sensor module 24b. Similarly, FIG.5 (c)-FIG.5 (e) are figures which show an example of the time change of the amplitude of reflected light R3-R5 which injects into the light receiver 15 among the reflected light which arose in sensor module 24c-24e. It is. FIG. 5F is a diagram illustrating reflected light R0 obtained by combining the reflected lights R1 to R5 incident on the light receiver 15.

  5A to 5F show the reference light SR having a constant amplitude for comparison. The amplitudes of the reflected lights R0 to R5 are normalized by the amplitude of the reference light SR. Further, in FIGS. 5A to 5E, since the scale of the vertical axis is changed, the waveform of the reference light SR shown in each figure is different at first glance, but the reference light SR is different. Note that the waveforms are identical.

  Considering a state in which an external force is applied to all of the optical sensors 26 provided in the sensor modules 24a to 24e, and assuming that measurement light enters the optical fiber portion 14 from the circulator 13 in this state, the sensor modules 24a to 24e Reflected light is generated in each, and the reflected light sequentially enters the light receiver 15 via the optical circulator 13. There is a difference in the optical path length until the measurement light reaches the reflecting member 25 of each sensor module 24a-24e, and the optical path length until the reflected light generated by each sensor module 24a-24e reaches the light receiver 15. Therefore, as shown in FIGS. 5A to 5E, the reflected lights R1 to R5 sequentially enter the light receiver 15 in this order.

As shown in FIGS. 5A to 5E, the amplitude of the reflected light R1 is the largest, the amplitude gradually decreases in the order of the reflected lights R2 to R4, and the amplitude of the reflected light R5 is the smallest. . Referring to the reflected light R0 shown in FIG. 5 (f) obtained by synthesizing these reflected lights R1 to R5, the reflected light R1 becomes dominant and the other reflected lights R2 to R5 can hardly be discriminated. Thus, when the difference in amplitude of the reflected lights R1 to R5 is large, it is difficult for the phase detector 16 to detect the phases φ _{B to} φ _E in the above-described equation (9).

上記（１０）式を参照すると、各反射波の振幅はＰ_０と一定であるため、各反射波の位相φ_Ａ〜φ_Ｅを検出することが可能となる。 Next, each of the sensor modules 24a to 24e is provided with an attenuator 27, and the attenuation amount of these attenuators 27 is incident on the light receiver 15 among the reflected light generated by the sensor modules 24a to 24e. Consider a case where the reflected light intensity is set to be the same. In such a case, the reflected light received by the light receiver 15 is expressed by the following equation (10).

Referring to the above equation (10), the amplitude of each reflected wave is constant at P ₀ , so that the phases φ _{A to} φ _E of each reflected wave can be detected.

  FIG. 6 is a diagram illustrating an example of reflected light having a constant amplitude incident on the light receiver 15. In FIG. 6, time is plotted on the horizontal axis and amplitude is plotted on the vertical axis, as in FIG. Further, in FIGS. 6A to 6E, similarly to FIGS. 5A to 5E, the reflected light generated by the sensor modules 24a to 24e is incident on the light receiver 15. An example of the time change of the amplitude of reflected light R1 to R5 is shown. FIG. 6F is a diagram showing reflected light R0 obtained by combining reflected lights R1 to R5 incident on the light receiver 15.

  6A to 6F also show the reference light SR having a constant amplitude for comparison, and the amplitudes of the reflected lights R0 to R5 are the same as the amplitude of the reference light SR. Yes. As shown in FIG. 6A to FIG. 6E, the reflected lights R1 to R5 have the same amplitude, but the reflected light R0 shown in FIG. Referring to it, it can be seen that the amplitude changes in a transient state (a state in which the number of reflected light incident on the light receiver 15 changes).

  FIG. 7 is a diagram for explaining the phase relationship of each reflected wave incident on the light receiver 15. FIG. 7A shows reflected light R0 obtained by combining reflected lights R1 to R5 incident on the same light receiver 15 as FIG. 6F. In the period T1 in FIG. 7A, only the reflected light R1 generated by the sensor module 24a enters the light receiver 15. For this reason, if the phase comparator 16 detects the phase of the voltage signal Sr output from the light receiver 15, the position where the reflected light is generated (the optical sensor 26 to which the external force is applied) can be specified.

  In contrast, in the period T2 in FIG. 7A, the reflected light R1 generated by the sensor module 24a and the reflected light R2 generated by the sensor module 24b are incident on the light receiver 15. For this reason, the amplitude of the reflected light R0 is a combination of these. Here, when the reflected lights R1 and R2 are represented in the phase space, they are represented by vectors V1 and V2 in FIG. 7B, and the reflected light R0 is represented by a vector V11 obtained by combining the vectors V1 and V2.

  Next, in a period T3 in FIG. 7A, the reflected light R1 generated by the sensor module 24a, the reflected light R2 generated by the sensor module 24b, and the reflected light R3 generated by the sensor module 24c enter the light receiver 15. To do. Therefore, when the reflected light R0 obtained by combining these reflected lights R1 to R3 is represented in the phase space, the vector V11 obtained by combining the vectors V1 and V2 and the vector V3 of the reflected light R3 are combined as shown in FIG. 7C. Represented by the vector V12.

  7A, the reflected light R1 generated by the sensor module 24a, the reflected light R2 generated by the sensor module 24b, the reflected light R3 generated by the sensor module 24c, and the sensor module 24d. The reflected light R4 enters the light receiver 15. Accordingly, when the reflected light R0 obtained by combining these reflected lights R1 to R4 is represented in the phase space, the vector V12 obtained by combining the vectors V1 to V3 and the vector V4 of the reflected light R4 are combined as shown in FIG. Represented by the vector V13.

  Further, in the period T5 in FIG. 7A, the reflected light R1 generated by the sensor module 24a, the reflected light R2 generated by the sensor module 24b, the reflected light R3 generated by the sensor module 24c, and the reflected light generated by the sensor module 24d. The light R4 and the reflected light R5 generated by the sensor module 24e enter the light receiver 15. Accordingly, when the reflected light R0 obtained by combining these reflected lights R1 to R5 is represented in the phase space, the vector V13 obtained by combining the vectors V1 to V4 and the vector V5 of the reflected light R5 are combined as shown in FIG. Represented by the vector V14.

  As described above, when the number of reflected lights incident on the light receiver 15 changes, the amplitude and phase of the reflected light R0 obtained by combining the reflected lights incident on the light receiver 15 change. This change appears only when the change occurs transiently and does not appear in a steady state where the number does not change. Since the optical distance of each of the optical sensors 26 with respect to the circulator 13 is known, the phase detector 16 detects the phase when the phase change occurs, and the determination unit 17 determines the phase as vectors V1 to V5. It is possible to determine which of the sensor modules 24a to 24e has caused the reflection, that is, which of the optical sensors 26 has been subjected to an external force by performing the process of disassembling. By laying the sensor modules 24a to 24e including the optical sensor 26 at different locations based on the above principle, it is possible to detect external force at a plurality of locations.

  As described above, according to the present embodiment, since it is not necessary to detect a specific wavelength or weak backscattered light with high accuracy, the position where the external force is applied to the optical fiber is detected without a significant increase in cost. be able to. Moreover, the optical fiber part 14 provided with the sensor module mentioned above can be applied to the crime prevention system which detects the intruder who invades in the site by laying it on a fence or the like installed at the site boundary, for example.

  In addition, although the example provided with the five sensor modules 24a-24e was demonstrated in the said embodiment, the number of sensor modules can be made into arbitrary numbers. In implementation, a rectangular wave may be used in addition to a sine wave as the modulated signal, and the modulated signal may be superimposed on the light emitted from the light source 11 as a modulation method, or intermittently. Alternatively, the modulated signal may be superimposed.

  Further, in the above embodiment, the optical sensor 26 is in a state where the measurement light leaks from the core to the clad and is absorbed by the clad when no external force acts, and the measurement light that travels inside the branch optical fiber when the external force acts. However, when the external force is not applied, the measurement light and the reflected light traveling inside the branch optical fiber are transmitted and the external force is not transmitted. In the state of acting, one that absorbs the measuring light can be used.

  Further, in the above embodiment, the attenuator 27 having a known attenuation amount is provided in each sensor module, and the amplitude of the reflected light incident on the light receiver 15 is made constant. The attenuator 27 can be omitted if an optical sensor having That is, the optical sensor and the attenuator can be integrated.

It is a mimetic diagram showing the whole external force detection device composition by one embodiment of the present invention. It is a block diagram which shows the structure of the sensor module 24a. 2 is a block diagram showing an internal configuration of a phase detector 16. FIG. It is the figure which represented the signals X and Y output from LPF32a, 32b in phase space. It is a figure which shows an example of the reflected light from which the amplitude which injects into the light receiver 15 differs. FIG. 4 is a diagram illustrating an example of reflected light having a constant amplitude that enters the light receiver 15. It is a figure for demonstrating the phase relationship of each reflected wave which injects into the light receiver.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 External force detection apparatus 11 Light source 12 Modulator 15 Light receiver 16 Phase detector 17 Judgment part 21a-21d Optical fiber for transmission 23a-23e Branching optical fiber 24a-24e Sensor module 25 Reflective member 26 Optical sensor 27 Attenuator

Claims (8)

A light source device that outputs measurement light whose intensity is modulated; a light receiving device that receives return light obtained by inputting the measurement light to an optical transmission path; and a phase of a light reception signal from the light receiving device to detect the phase In an external force detection device comprising a determination device that determines the presence or absence of an external force action on an optical transmission line,
At least one branched optical transmission line provided to be branched with respect to the optical transmission line;
A sensor module that is provided at an intermediate portion of the branched light transmission path, changes the return light depending on the presence or absence of an external force, and sets the amplitude of the return light received by the light receiving device to a predetermined value. An external force detection device characterized by. The sensor module is an optical sensor that switches between a state of transmitting light and a state of absorbing light depending on the presence or absence of an external force; and
The external force detection device according to claim 1, further comprising: an attenuator that sets a return light amplitude returning from the branch light transmission path to the light receiving device to a predetermined value.   Each attenuator provided in the branched light transmission path is set to have an attenuation amount so that the amplitude of the return light returning from each of the branched light transmission paths to the light receiving device becomes a constant value. The external force detection device according to claim 2.   4. The external force detection device according to claim 2, wherein the optical sensor and the attenuator are integrated. The light source device includes a light source, and light modulation means for outputting, as the measurement light, intensity-modulated light obtained by intensity-modulating the output light of the light source using a predetermined modulated signal,
The determination device includes: a phase detector that detects a phase difference between an envelope of the light reception signal and an envelope of the modulated signal; and whether the external force is applied based on a phase detection signal of the phase detector. The external force detection device according to claim 1, further comprising: a determination unit that determines.   The external force detection device according to claim 5, wherein the determination unit determines which external force is applied to any of the optical sensors based on a change in the phase detection signal.   The external force detection device according to any one of claims 1 to 6, wherein the branched light transmission path includes a reflection member that reflects the measurement light and generates reflected light at an end thereof. 7. The external force detection device according to claim 1, wherein an end of the branched light transmission path is a reflection end that reflects the measurement light and generates reflected light. 8. .

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