JP2008309497A - Fiber optic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber optic sensor for achieving low prices and compactness and specifying the positions of occurrences of displacement in monitoring areas. <P>SOLUTION: The fiber optic sensor comprises a sensor unit having a semiconductor laser 1; a plastic optical fiber 2 joined to the semiconductor laser 1 for the multi-mode propagation of its output light; and a photo-diode 3 for receiving only part of output light of the plastic optical fiber 2, and a determination detection part 32 for outputting detection results on the basis of the frequency and amplitude of output electric signals from the photo-diode 3. The plastic optical fiber 2 is mounted to a monitoring area 5 to detect vibrations and displacements added to the plastic optical fiber 2 in the monitoring area 5. A fiber fixing part 23 directly joins output of the semiconductor laser 1 to an incident face of the plastic optical fiber 2. The semiconductor laser 1 and the photo-diode 3 are integrally packaged as a light-transmitting and receiving part 31. The light-transmitting and receiving part 31 and the determination detection part 32 are spatially separated from each other, but connected to each other by an electric cable 33. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical fiber sensor that detects vibration and displacement applied to an optical fiber from light emitted from the optical fiber, and in particular, monitoring of vibration in a relatively narrow region using a plastic optical fiber or the like is inexpensive. The present invention relates to an optical fiber sensor to be realized.

  Fiber optic sensors are generally not affected by lightning or electromagnetic noise generated by electrical devices, are easily monitored remotely, and have superior environmental resistance compared to electrical wires. It is used in various fields. For example, in security measures, detection of vibrations caused by intruders in buildings, premises, fences, etc., and in safety monitoring and disaster countermeasures, vibrations in structures such as buildings and bridges, specific ground, etc. It is used for detecting the occurrence of distortions and for detecting temperature distribution over a wide range.

  There are several types of optical fiber sensors depending on the operating principle. As these methods, Brillouin scattered light, Rayleigh scattered light, and Raman scattered light generated when pulsed light is incident on the optical fiber are detected, and the frequency shift, scattered light intensity, attenuation, arrival time, etc. are applied to the optical fiber. First method to detect applied strain, displacement, temperature, distribution of them, FBG (Fiber Bragg Grating) is inserted into the optical fiber in the monitoring area, and the wavelength characteristics of the reflected light due to stretching strain to FBG A second method for detecting a change, a third method for detecting a change in mode distribution in the multimode optical fiber due to strain or vibration, and the like are mainly used. .

Of the various methods described above, the first type of optical fiber sensor is generally capable of detecting with high sensitivity over a long monitoring area of several tens of kilometers or more, and is capable of specifying the position where a displacement occurs. However, it requires a high-performance optical device, component, and electric circuit for the light source and detection system, which results in a very expensive apparatus. The optical fiber sensor of the second system can specify the generation position of vibration or the like by changing the grating period of the FBG depending on the monitoring location, but it has sensitivity only in the portion where the FBG is inserted in the optical fiber. In addition, the FBG itself is an expensive part, and the wavelength detection system also requires an expensive part, so that the entire system becomes expensive.

  On the other hand, the third type optical fiber sensor can be realized with a relatively simple configuration as described in Patent Documents 1 to 3, and an optical fiber sensor using this principle has been put into practical use.

  9A and 9B are diagrams for explaining a conventional optical fiber sensor of this system. FIG. 9A is a configuration diagram, and FIG. 9B is a light distribution at the optical fiber output end of the multimode optical fiber. FIG.

  9A, light emitted from a light source 91 such as a semiconductor laser is incident on a multimode optical fiber 93 by a lens 92, and a part of the output is incident on a single mode optical fiber 95 at an output end 94 thereof. The light that has passed through the single-mode optical fiber 95 is incident on a light receiver 97 such as a photodiode by a lens 96 and detected. Here, the light incident on the multi-mode optical fiber 93 is propagated with its energy distributed in a plurality of modes, and the light distribution at the exit end 94 is an optical fiber as schematically shown in FIG. 9B. A complex speckle pattern 99 is generated by the interference of light of each propagation mode in the core 98. Here, when any portion of the multimode optical fiber 93 is displaced, the speckle pattern 99 changes, so that, for example, only light near the center is coupled to the single mode optical fiber 95 having a small core diameter at the emission end 94. If extracted, the amount of light changes according to the amount of displacement, and the displacement is detected by the light receiver 97. Coupling portions such as the light source 91, the light receiver 97, and the lenses 92 and 96 are accommodated in the apparatus main body 102 together with the control processing circuit portion 101 that determines the detection result.

U.S. Pat. No. 4,297,684 JP-A-57-8898 JP 57-197420 A

  Currently, optical fiber sensors are practically used in large-scale systems such as monitoring systems in large-scale civil engineering fields as described above, security systems in large-scale facilities such as airports and large factories. limited. This is mainly due to the expensive equipment. In addition, the control of the light source and the detection signal and the processing circuit are complicated, and the size of the control device is increased. If a low-priced, small-sized optical fiber sensor can be realized, it can be used for general factories, buildings such as buildings, and even small-scale systems such as private houses, and its application can be greatly expanded.

  As described above, the optical fiber sensor of the third method is simpler than the other methods, and can be detected over the entire length of the optical fiber of about 2 km. There is a disadvantage that the position where it occurs cannot be specified. Also, when constructing an actual device, it is necessary to have a structure that ensures high-precision adjustment of the optical system such as the lens at the entrance and exit from the semiconductor laser to the optical fiber and the mounting reliability, etc. Due to the need for manufacturing costs, the use of quartz optical fiber with low loss, the price is high, and the control part for judging the detection result is complicated, which makes the entire device expensive and large. It cannot be used practically for small-scale applications as described above.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber sensor that can be manufactured at a low cost and can be reduced in size, and that can specify a position where a displacement or the like occurs in a monitoring area.

  In order to solve the above problems, an optical fiber sensor according to the present invention includes a semiconductor laser that outputs visible light, a plastic optical fiber that is coupled to the semiconductor laser and propagates the output light in a multimode, and output light of the plastic optical fiber. A sensor unit that receives a part of the photodiode, and a determination detection unit that outputs a determination result based on the frequency and amplitude of the electrical signal output from the photodiode, and monitors the plastic optical fiber It is installed in a region, and at least one of vibration, stress, strain, and displacement applied to the plastic optical fiber in the monitoring region is detected.

  Here, the output of the semiconductor laser is directly coupled to the incident end face of the plastic optical fiber, and the outgoing light emitted from the outgoing end face of the plastic optical fiber is converted into the output light containing 50% of the energy of the outgoing light. Directly coupled to a photodiode having a light receiving surface smaller than the cross section of the central portion, the package containing the semiconductor laser, the incident end face of the plastic optical fiber, the package containing the photodiode, and the output of the plastic optical fiber The fixing portion for the plastic optical fiber may be installed so that the relative positions of the end faces are fixed.

  The semiconductor laser and the photodiode may be integrally mounted as a light transmission / reception unit, the light transmission / reception unit and the determination detection unit may be spatially separated, and an electrical cable may be connected between them.

  In addition, a plurality of the sensor units may be arranged in multiple stages, and the photodiodes of the preceding sensor unit and the semiconductor laser of the succeeding sensor unit may be disposed close to each other. The photodiode and the next-stage semiconductor laser may be integrally mounted as a light transmitting / receiving unit.

  Also, an output signal transmission unit comprising a light source for converting the detection result into an optical signal, a transmission optical fiber for transmitting the optical signal, and a light receiver for receiving the optical signal is disposed in parallel with each sensor unit. Provided in multiple stages, and in each output signal transmission unit, the output of the detection result of the previous sensor unit and the signal for distinguishing each monitoring region are added to the output obtained from the output signal transmission unit of the previous stage and obtained by the light receiver. The detection result in each monitoring area may be sequentially transmitted by modulating the light source to generate an optical signal.

  Here, one plastic optical fiber in an optical fiber cord containing at least two plastic optical fibers is used as the plastic optical fiber of the sensor unit, and the other one is used for transmission of the output signal transmission unit. It may be used as an optical fiber.

  Further, the light transmission / reception unit, the determination detection unit, and the means for modulating the light source to generate an optical signal may be integrally mounted as an interface unit.

  In each of the above configurations, the determination detection unit includes an amplifier of the output electric signal, a filter circuit that selects a frequency, a comparison circuit that determines an amplitude, and an output circuit that outputs a determination result, and the filter circuit and the comparison circuit May be configured to be adjustable.

  As described above, in the present invention, an inexpensive optical fiber sensor is realized by using an inexpensive plastic optical fiber having a large core diameter as a multimode optical fiber and performing direct coupling with a semiconductor laser with a simple structure. Is. In the conventional optical fiber sensor, the core diameter of the silica optical fiber is 50 μm to 65 μm, and for coupling with the semiconductor laser, the detection sensitivity of the optical fiber propagation mode is increased by using a lens or the like as shown in FIG. In the present invention, as a result of experiments by the inventors, the light emitted from the semiconductor laser is directly coupled to a plastic optical fiber having a core diameter of 500 μm to 1000 μm by a simple method. However, it is confirmed that the necessary sensitivity due to vibration and displacement can be obtained, and for applications where it is not necessary to strictly define the detection and judgment targets such as vibration and displacement as in the past, This is based on the confirmation that necessary vibrations can be determined with a simple control circuit.

  In addition, although the plastic optical fiber has a large loss, it can be sufficiently used in a narrow region of about several tens of meters. In addition, since the optical fiber sensor of the present invention is inexpensive, it is practically possible to individually arrange it for each monitoring area that is divided into narrow sections. It is possible to specify the position where it occurred.

  In this case, the semiconductor laser, the plastic optical fiber, and the photodiode can be separated from each other as one independent sensor unit. However, a plurality of optical fiber sensor units are arranged in the preceding photodiode and the next semiconductor. It is also possible to arrange the lasers in multiple stages so that the lasers are integrated. In this case, using a multi-core optical fiber cord, one of them is an optical fiber for displacement detection, and the other is an output result transmission. If used as an optical fiber, the output result can be transmitted without laying a new optical fiber cord.

  As described above, according to the present invention, it is possible to obtain an optical fiber sensor that is inexpensive and can be miniaturized and that can specify a position where a displacement or the like is generated in a monitoring region.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of a first embodiment of an optical fiber sensor according to the present invention. 1, the optical fiber sensor of the present embodiment includes a semiconductor laser 1 that outputs visible light, a plastic optical fiber 2 that is coupled to the semiconductor laser 1 and propagates the output light in a multimode, and an output of the plastic optical fiber 2. A plastic optical fiber having a sensor unit including a photodiode 3 that receives only a part of light and a determination detection unit 4 that outputs a detection result based on the frequency and amplitude of an electric signal output from the photodiode 3 2 is installed in the monitoring area 5 to detect vibration and displacement applied to the plastic optical fiber 2 in the monitoring area 5. Here, when the monitoring area 5 is an intrusion monitoring place such as a passage in a building, an outdoor site, or a fence, the plastic optical fiber 2 is laid on the carpet in the passage, the ground, the fence surface, or the like. As the plastic optical fiber 2, a cable coated with an environment-resistant coating and coded for outdoor use can be used.

  FIG. 2 is a cross-sectional view showing an example of the mounting structure of the incident end of the semiconductor laser 1 and the plastic optical fiber 2 of the optical fiber sensor of the above embodiment, and FIG. 3 shows the emission end of the plastic optical fiber 2 and the photodiode 3. It is sectional drawing which shows an example of the mounting structure.

  In FIG. 2, the output of the semiconductor laser 1 is directly coupled to the incident end face of the plastic optical fiber 2. For this purpose, the package 21 containing the semiconductor laser 1 and the incident portion 22 having the incident end face of the plastic optical fiber 2 are fixed to the laser casing 24 having the fiber fixing portion 23 by adjusting their relative positions. Further, in FIG. 3, a photodiode 3 having a light receiving surface smaller than the cross section of the central portion in which 50% of the energy of the emitted light emitted from the end surface of the plastic optical fiber 2 is directly coupled. A light emitting portion 26 having a package 25 in which the photodiode 3 is incorporated and a light emitting end surface of the plastic optical fiber 2 is fixed to a PD housing 28 having a fiber fixing portion 27 by adjusting their relative positions. Here, vibration or the like can be detected by receiving a part of the energy of the central portion of the emitted light. However, in order to obtain the required sensitivity, the amount of received light should be 50% or less of the total emitted light energy. Is desirable.

  The core diameter of the plastic optical fiber 2 is about 500 to 1000 μm, which is much larger than that of a normal quartz optical fiber. Therefore, the number of propagation modes is very large, and even if the coupling state with the semiconductor laser 1 changes slightly, the propagation mode Since a large number of states can be easily obtained, and a sufficient change in the speckle pattern at the exit end corresponding to displacement such as vibration can be obtained, the above mounting structure has a high-precision coupling as in the past. Is unnecessary. For this reason, the processing accuracy of the fiber fixing portion 23 may be low, and the plastic optical fiber 2 can be fixed by pressing it with a removable screw 29 or the like through a contact plate. In addition, since the core diameter is large as described above, the speckle pattern spreads widely, and even if the relative position of the photodiode 3 that receives a part of the light amount with respect to the emission end of the plastic optical fiber 2 slightly changes, it is sufficient. Since the sensitivity is obtained, the processing accuracy of the fiber fixing portion 27 and the fixing of the plastic optical fiber 2 to the fiber fixing portion 27 can be easily performed similarly to the fiber fixing portion 23. If the plastic optical fiber 2 is coded, the coating at the entrance end and exit end is removed and inserted into the fiber fixing portions 23 and 27, and the boundary with the coating is filled with waterproof resin or the like. Environmental resistance is obtained.

  As described above, the optical fiber sensor according to the present embodiment uses the mounting structure shown in FIGS. 2 and 3 so that a lens, an optical fiber connector, and the like are unnecessary, and a plastic optical fiber is also inexpensive, so that the optical system portion is inexpensive. Since the structure is simple, the shape of the portion can be reduced in size. Furthermore, since the plastic optical fiber 2 can be easily attached to the fiber fixing portions 23 and 27, the replacement when the plastic optical fiber 2 is damaged is very easy.

  In addition, the determination detection unit in FIG. 1 amplifies an electric signal detected by the photodiode 3 with an amplifier, passes a signal in a band from about 10 Hz to about several kHz set in advance by a filter circuit, for example, and sets the amplitude in advance. This is a circuit that compares the specified voltage with the set circuit and outputs the result. The above band and the specified voltage are adjusted based on the frequency and sensitivity of the vibration that needs to be detected in the monitoring area after the circuit is mounted. It is configured to be possible. In this case, the determination detection unit can be simplified by adopting a circuit configuration for determination based only on the frequency and amplitude of the electric signal, and this part can also be reduced in price and size.

  The output of the determination result can be set in accordance with the overall system requirements such as contact signal, analog signal, digital signal, etc., and the determination result is transmitted as an optical signal as described later. It is also possible to obtain a signal suitable for the above.

  FIG. 4 is a configuration diagram of a second embodiment of the optical fiber sensor according to the present invention. In FIG. 4, the basic components are the same as those of the embodiment of FIG. 1, but in this embodiment, the semiconductor laser 1 and the photodiode 3 are integrally mounted as a light transmitting / receiving unit 31, and the light transmitting / receiving unit 31 31 and the determination detection unit 32 are spatially separated, and an electric cable 33 connects between them.

  4, the structure of the coupling and fixing part of the semiconductor laser 1 and the plastic optical fiber 2 and the structure of the fixing part of the photodiode 3 and the plastic optical fiber 2 are the same as those in FIG. 2, except that the semiconductor laser 1 is incorporated. The package 21 and the package 25 in which the photodiode 3 is built are fixed to a common housing and constitute a light transmitting / receiving unit 31. The control of the semiconductor laser 1 of the light transmission / reception unit 31 and the processing of the optical signal from the photodiode 3 are performed by the determination detection unit 32 connected by the electric cable 33. A current output circuit 34 for driving the semiconductor laser 1 and an amplification circuit 35 for amplifying an electric signal photoelectrically converted by the photodiode are incorporated. The current output circuit 34 may include a circuit for driving by high frequency superimposition in order to reduce noise of the semiconductor laser 1.

  The optical fiber sensor of the present embodiment is easy to miniaturize because the light transmitting / receiving unit 31 has a simple configuration, and is separated from the determination detecting unit 32 and is a sensor unit comprising the light transmitting / receiving unit 31 and the plastic optical fiber 2. Can be installed in the monitoring area 5 only.

  FIG. 5 and FIG. 6 are diagrams showing an example in which the sensor unit of the optical fiber sensor according to the present embodiment is arranged in a plurality of monitoring areas. FIG. 5 controls the determination detection unit in each monitoring area in common. FIG. 6 shows a configuration in the case of monitoring, and FIG. 6 shows a configuration in which a determination detection unit is provided for each monitoring area and the output is transmitted on the data transmission path.

  In FIG. 5, plastic optical fibers 44, 45, and 46 are laid in continuous monitoring areas 41, 42, and 43, respectively, and electrical cables from the respective transmission / reception units 47, 48, and 49 are connected to a common determination / detection unit 50. In the determination detection unit 50, the detection signals from the transmission / reception units are separated and discriminated to thereby detect the occurrence of vibration and the like in each monitoring region separately. In FIG. 6, determination detection units 51, 52, and 53 connected to each transmission / reception unit are provided for each monitoring area, and the output is converted into a proper data format and illustrated by the data transmission path 54. Not sent to a centralized management device etc. In this case, a communication circuit that converts the determination result output into transmission data may be installed in each of the determination detection units 51, 52, and 53, and a television camera or an object detection sensor installed in the same monitoring area may be installed. Monitoring information can be comprehensively managed by adding a function to synthesize and transmit signals from other sensors to the communication circuit.

  FIG. 7 is a configuration diagram of a third embodiment of an optical fiber sensor according to the present invention. In FIG. 7, the basic components are the same as those of the embodiment of FIG. 1, and similarly to the second embodiment, a semiconductor laser and a photodiode are integrally mounted as a light transmitting / receiving unit. Similarly, a sensor unit is arranged in each monitoring area. However, in the present embodiment, a plurality of sensor units arranged in multiple stages are installed so that the photodiodes of the preceding sensor unit and the semiconductor laser of the next sensor unit are arranged close to each other. A photodiode at the front stage of the unit and a semiconductor laser at the next stage are integrally mounted as a light transmitting / receiving section.

  That is, in FIG. 7, the photodiode 63 of the first-stage sensor unit having the plastic optical fiber 62 arranged in the monitoring area 41 and the second-stage sensor unit having the plastic optical fiber 65 arranged in the monitoring area 42. The semiconductor laser 64 of the third stage is integrally mounted as a light transmitting / receiving unit 68-1 and includes the photodiode 66 of the second stage sensor unit and the plastic optical fiber 69 disposed in the monitoring region 43. 67 is integrally mounted as a light transmitting / receiving unit 68-2. As these light transmitting / receiving units 68-1 and 68-2, it is possible to use the same structure as the light transmitting / receiving unit 31 shown in FIG. 4, and the plastic optical fiber is 180 degrees opposite as shown in FIG. It is also possible to have a structure that is coupled so that it can be pulled out in the direction. Although FIG. 7 shows a case where the determination detectors 71 and 72 are provided independently for the light transmitting / receiving units 68-1 and 68-2, respectively, a common determination detection unit may be provided as in FIG. . Similarly to the case of FIG. 6, a communication circuit for converting the determination result output into transmission data is installed in each of the determination detection units 71 and 72, and signals of other sensors installed in the same monitoring area are combined. Thus, the monitoring information can be comprehensively managed by adding the function of transmitting to the communication circuit.

  FIG. 8 is a configuration diagram of a fourth embodiment of an optical fiber sensor according to the present invention. In FIG. 8, the arrangement of the sensor units and the basic configuration of the light transmission / reception unit are the same as those in the embodiment of FIG. 7, but in this embodiment, a determination detection unit is provided for each sensor unit and the detection is performed. An output signal transmission unit comprising a light source for converting the result into an optical signal, a transmission optical fiber for transmitting the optical signal, and a light receiver for receiving the optical signal is provided in multiple stages in parallel with the sensor units, In each output signal transmission unit, the monitoring area in which the output of the detection result of the next sensor unit and the multimode optical fiber of each sensor unit are installed in the output transmitted from the previous output signal transmission unit and obtained by the light receiver By adding a signal for identifying the light source and modulating the light source to generate an optical signal, detection results in each monitoring region can be transmitted sequentially.

  In FIG. 8, the electrical signal from the photodiode 63 of the first-stage sensor unit is detected and determined by a determination control circuit 81 including a first-stage determination detection unit and a control circuit for the second-stage semiconductor laser 64. The detection result is converted into optical signal data by modulating the light source 83 by the communication control circuit 82 that adds the identification information of the monitoring area 41 and converts it into an optical signal of a suitable code format. Is transmitted by a transmission optical fiber 84 juxtaposed with the plastic optical fiber 65.

  The optical signal data is received by the light receiver 85 at the output end of the transmission optical fiber 84, and the received data is detected from the photodiode 66 of the second-stage sensor unit and detected by the determination control circuit 86. And the identification information of the monitoring area 42 are added, and the light source 88 is modulated by the communication control circuit 87 to be converted into optical signal data, and the optical signal data is transmitted to the third-stage plastic optical fiber 69. It is transmitted by fiber 89. Here, the transmission optical fiber 84, the communication control circuit 87, the light receiver 85, and the light source 88 constitute a second-stage output signal transmission unit. By using the light sources 83 and 88 and the light receivers 80 and 85 that are the same as the semiconductor laser and photodiode of the sensor unit, respectively, the structure of the light transmission / reception unit of the sensor unit can be used in common. However, in this case, it is desirable that the photodiodes of the light receivers 80 and 85 can receive most of the light emitted from the transmission optical fiber in order to receive optical signal data without error. Further, since the light source 83, 88 has a low signal data rate, it is possible to use an LED. In this case, the influence of speckle pattern generation due to interference in optical signal transmission can be reduced. The light receiving diameter of can be reduced.

  Also, as shown in FIG. 8, the above-described sensor unit transmitter / receiver unit, light source / receiver unit, determination control circuit, and communication control circuit are integrally mounted in one housing to form interface units 75 and 76. This simplifies the work of installing the optical fiber sensor in each monitoring area, and facilitates the management and maintenance of the optical fiber sensor system. Furthermore, one of the two-core optical fiber cables containing two multimode optical fibers should be used as the multimode optical fiber of the sensor unit, and the other one should be used as the transmission optical fiber of the output signal transmission unit. This simplifies the laying of the optical fiber, eliminates the need for a data transmission path installation space for signal transmission, and facilitates maintenance. Further, the monitoring information can be comprehensively managed by adding a function of synthesizing and transmitting signals from other sensors installed in the same monitoring area to the communication control circuit.

  As described above, according to the present invention, it is possible to obtain an optical fiber sensor that is inexpensive and can be miniaturized, and that can specify a position where a displacement or the like occurs in a monitoring area.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of 1st embodiment of the optical fiber sensor by this invention. Sectional drawing which shows an example of the mounting structure of the incident end of a semiconductor laser and a plastic optical fiber. Sectional drawing which shows an example of the mounting structure of the output end of a plastic optical fiber, and a photodiode. The block diagram of 2nd embodiment of the optical fiber sensor by this invention. It is a figure which shows the example in the case of arrange | positioning a sensor unit in a some monitoring area | region, and is a block diagram in the case of carrying out control monitoring by sharing the determination detection part of each monitoring area | region. It is a figure which shows the example in the case of arrange | positioning a sensor unit in several monitoring area | regions, and is a block diagram in the case of providing the determination detection part for every monitoring area | region, and transmitting the output on a data transmission line. The block diagram of 3rd embodiment of the optical fiber sensor by this invention. The block diagram of 4th embodiment of the optical fiber sensor by this invention. It is a figure for demonstrating the conventional optical fiber sensor, Fig.9 (a) is a block diagram, FIG.9 (b) is a figure which shows the light distribution in the optical fiber output end of a multimode optical fiber.

Explanation of symbols

1, 61, 64, 67 Semiconductor laser 2, 44, 45, 46, 62, 65, 69 Plastic optical fiber 3, 63, 66 Photodiode 4, 32, 50, 51, 52, 53, 71, 72 Determination detection unit 5, 41, 42, 43 Monitoring area 21, 25 Package 22 Incident part 23, 27 Fiber fixing part 24 Laser housing 26 Emitting part 28 PD housing 29 Screws 31, 47, 48, 49, 68-1, 68-2 Transmitter / receiver unit 33 Electric cable 34 Current output circuit 35 Optical signal amplifier circuit 54 Data transmission path 81, 86 Determination control circuit 82, 87 Communication control circuit 75, 76 Interface unit
83, 88, 91 Light source 80, 85, 97 Light receiver 84, 89 Transmission optical fiber 92, 96 Lens 93 Multimode optical fiber 94 Outlet end 95 Single mode optical fiber 98 Core 99 Speckle pattern 101 Control processing circuit portion 102 Main unit

Claims (9)

  A sensor unit comprising: a semiconductor laser that outputs visible light; a plastic optical fiber that is coupled to the semiconductor laser and propagates the output light in multimode; and a photodiode that receives a part of the output light of the plastic optical fiber; A determination detection unit that outputs a determination result based on the frequency and amplitude of the output electrical signal from the photodiode, and the vibration that is applied to the plastic optical fiber in the monitoring region by installing the plastic optical fiber in the monitoring region An optical fiber sensor that detects at least one of stress, strain, and displacement.   The output of the semiconductor laser is directly coupled to the incident end face of the plastic optical fiber, and the outgoing light emitted from the outgoing end face of the plastic optical fiber is converted into the central portion of the outgoing light including 50% of the energy of the emitted light. The plastic optical fiber is directly coupled to a photodiode having a light receiving surface smaller than a cross-section, the incident end surface of the plastic optical fiber is in the package containing the semiconductor laser, and the plastic optical fiber is in the package containing the photodiode. The optical fiber sensor according to claim 1, further comprising a fixing portion on which the plastic optical fiber is installed so that the emission end faces of the optical fiber are positioned respectively.   The semiconductor laser and the photodiode are integrally mounted as a light transmission / reception unit, the light transmission / reception unit and the determination detection unit are spatially separated, and an electrical cable is connected between them. The optical fiber sensor according to claim 1 or 2.   The plurality of sensor units are arranged in a plurality of stages, and the photodiodes of the preceding sensor unit and the semiconductor laser of the next sensor unit are arranged so as to be arranged close to each other. An optical fiber sensor described in 1.   5. The optical fiber sensor according to claim 4, wherein a front-stage photodiode and a next-stage semiconductor laser of each sensor unit are integrally mounted as a light transmission / reception unit.   An output signal transmission unit composed of a light source for converting the detection result into an optical signal, a transmission optical fiber for transmitting the optical signal, and a light receiver for receiving the optical signal is juxtaposed with each sensor unit in multiple stages. In each output signal transmission unit, the output of the detection result of the next sensor unit and the multimode optical fiber of each sensor unit are installed in the output transmitted from the previous output signal transmission unit and obtained by the light receiver. 6. The light according to claim 4 or 5, wherein a detection result in each monitoring area can be sequentially transmitted by adding a signal for identifying a monitoring area and modulating the light source to generate an optical signal. Fiber sensor.   One of the optical fiber cords including at least two plastic optical fibers is used as the plastic optical fiber of the sensor unit, and the other one is used as the transmission optical fiber of the output signal transmission unit. The optical fiber sensor according to claim 6, wherein the optical fiber sensor is used.   8. The optical fiber sensor according to claim 6, wherein the light transmission / reception unit, the determination detection unit, and a unit that modulates the light source to generate an optical signal are integrally mounted as an interface unit.   The determination detection unit includes an amplifier for the output electric signal, a filter circuit for selecting a frequency, a comparison circuit for determining an amplitude, and an output circuit for outputting a determination result. The filter circuit and the comparison circuit are adjusted. The optical fiber sensor according to claim 1, wherein the optical fiber sensor is configured to be possible.

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