JP2008157759A - Optical fiber sensor system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable vibrations at multiple detection points to be detected in a range up to a high-frequency band by using an optical fiber. <P>SOLUTION: Light of a wavelength-variable laser 11 is branched by using optical couplers 13, 15 and 18, and applied to a plurality of sensor sections S1, S2 and Sn. The sensor sections have reflecting plates 23, 26 and 29 respectively, each varying its refection point in accordance with the vibrations. Interference properties of etalons of the plurality of sensor sections are previously varied for respective sensor sections. The laser light of the wavelength-variable laser is scanned in a fixed wavelength range, and applied to the sensor sections, thereby obtaining a superimposed interference signal corresponding to the properties of the etalons. A photoelectric conversion and a Fourier transform are applied to this signal, and its frequency is separated in accordance with the etalon properties of the sensor sections, whereby signals of the sensor section at the multiple points can be detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical fiber sensor system for detecting vibration and sound using an optical fiber.

An optical fiber sensor using an optical fiber as a sensor is superior in reliability because it is not affected by electromagnetic noise compared to an electrical sensor. As an optical fiber sensing system, for example, an optical microbending method that measures the amount of bending using the attenuation of the amount of light passing through the bending of the optical fiber, or the fact that the frequency of the Brillouin scattered light is displaced by the elongation of the optical fiber is used. And the BOTDR method. In addition, there is a sensor that utilizes the fact that a reflection wavelength or a transmission wavelength is displaced by an optical fiber Bragg grating. A multipoint optical microphone system that detects multipoint acoustic signals using a broadband light source has also been proposed (Non-Patent Document 1).
Toshinari Watanabe et al., "Study on Multi-point Optical Microphone System Using FBG" IEICE Technical Report, Pn2005-78, OFT2005-65, OPE2005-126, LQE2005-141, P43-48

  However, the BOTDR method has a drawback in that it cannot measure in real time because the position is measured for each generated pulse, and is not suitable for measuring a signal. In addition, since the measurement location is local, there is a disadvantage that it is not suitable for urgent measurement such as multipoint measurement, wide-range measurement, and disaster. Furthermore, even in the multipoint FBG method, the conventional method has a drawback that it takes a long time to measure the wavelength variation with high sensitivity. Further, the conventional method has a drawback that the upper limit of the detectable frequency is about 10 kHz, and it is difficult to measure vibration up to 20 kHz like sound.

  The present invention has been made paying attention to such conventional problems, and an object thereof is to provide an optical fiber sensor system for detecting signals and sound at high speed by using a wavelength variable light source. .

  In order to solve this problem, an optical fiber sensor system according to the present invention includes a wavelength tunable laser that generates single-mode light whose wavelength periodically changes in a certain wavelength range, and light from the wavelength tunable laser. An optical branching unit that branches into the first and second branching beams, and the first branching beam branched by the optical branching unit is branched by a plurality of optical circulators connected in cascade through an optical fiber, and the reflected light is An optical circulator unit to synthesize, an optical circulator that further branches the second branched light of the optical branching unit, and a reference mirror unit that generates a reference light having a reference mirror that reflects light obtained from the optical circulator And the branched light beams separated by the optical circulator unit are respectively given, different reflection reference positions are set, and the respective reflection positions are changed by externally applied vibrations. A plurality of sensor units that generate and return to the optical circulator unit, an optical interference unit that causes the reflected light signal superimposed from the optical circulator unit to interfere with the reference light generated by the reference mirror unit, and the optical interference A light receiving unit that photoelectrically converts a difference between two interference waves whose phases are inverted from each other, a Fourier transform unit that converts a received light signal obtained by the light receiving unit into a frequency domain signal by Fourier transform, and the Fourier transform A frequency separation unit that extracts the Fourier transform signal corresponding to the signal from each sensor unit by separating the generated signal in the frequency domain, and a signal from each sensor unit separated by the frequency separation unit in the time domain And a Fourier inverse transform unit that inversely transforms the signal.

  Here, each of the sensor units may irradiate the branched light to the vibration source to be measured and receive the reflected light.

  In order to solve this problem, an optical fiber sensor system according to the present invention includes a wavelength tunable laser that generates single-mode light whose wavelength periodically changes in a certain wavelength range, and light from the wavelength tunable laser. An optical fiber and an optical coupler for branching and coupling the optical fiber, branching the laser light from the wavelength tunable laser into a plurality of light and combining the reflected light, and branching from the light branching and combining unit The reflected light is branched, the light is branched, a different reflection reference position is set, and the reflected light whose reflection position is changed by vibration applied from outside is caused to interfere with the light branching and combining unit. A plurality of sensor units for guiding, a light receiving unit that receives the interference light combined by the light branching and combining unit and converts it into an electrical signal, and a Fourier transform of the light reception signal obtained by the light receiving unit A Fourier transform unit for converting the signal into a frequency domain signal, a frequency separation unit for separating the Fourier transformed signal in the frequency domain and extracting the Fourier transform signal corresponding to the signal from each sensor unit, and the frequency A Fourier inverse transform unit that inversely transforms a signal from each sensor unit separated by the separation unit into a signal in the time domain.

  Here, each of the sensor units may irradiate the branched light to the vibration source to be measured and receive the reflected light.

  Here, the sensor unit includes a beam splitter disposed at an angle of 45 ° with respect to the optical axis, and a mirror that reflects the light branched from the beam splitter and returns the light to the beam splitter, and interferes with the beam splitter. Light may be generated.

  In order to solve this problem, an optical fiber sensor system according to the present invention includes a wavelength tunable laser that generates single-mode light whose wavelength periodically changes in a certain wavelength range, and light from the wavelength tunable laser. And an optical coupler for branching and coupling the light, branching the laser light from the wavelength tunable laser, and branching the reflected light from the optical branching and combining unit for synthesizing the reflected light. A plurality of sensor units for setting reflected reference positions different from each other and guiding reflected light whose reflection positions are changed by externally applied vibrations to the light branching and combining unit, and the light branching and combining unit A reference reflection unit that guides the reference light to the optical fiber of the branching and combining unit by changing the branched light from the wavelength tunable laser at a reference reflection position, and the optical branching and combining unit. A light interference unit that causes interference between the reflected light obtained from the reference light and the reference light obtained from the reference reflection unit, a light receiving unit that receives the interference light obtained from the light interference unit and converts the light into an electrical signal, and the light receiving unit A Fourier transform unit that transforms the received light signal obtained into a frequency domain signal by Fourier transform, and the Fourier transform signal corresponding to the signal from each sensor unit by separating the Fourier transformed signal in the frequency domain A frequency separation unit for extraction, and a Fourier inverse transform unit that inversely transforms signals from the sensor units separated by the frequency separation unit into signals in the time domain.

  Here, each sensor unit may irradiate the branched light to the vibration source to be measured and receive the reflected light.

  According to the present invention having such a feature, it is possible to reproduce broadband vibrations and audio signals by using a single-mode light source and sufficiently increasing the scanning speed thereof, and signals from a plurality of vibration sources. The effect that can be analyzed is obtained. Further, according to the first and second aspects of the invention, since the optical circulator is used, the light utilization efficiency can be improved, and the vibration of each sensor unit can be detected with high sensitivity even in a detection system having a large number of sensor units. be able to.

  FIG. 1 is a diagram showing an overall configuration of an optical fiber sensor system according to Embodiment 1 of the present invention. In this embodiment, the wavelength tunable laser 11 is used as a light source. The wavelength tunable laser 11 is, for example, a laser light source that generates single-mode light in the 1.5 μm band and changes its wavelength. The wavelength range is, for example, 100 nm, and the wavelength is periodically scanned at a high speed. The light from this light source is input to the optical coupler 13 through the optical fiber 12. The optical coupler 13 separates the light from the wavelength tunable laser 11 and the reflected light, and the light from the wavelength tunable laser 11 is guided to the optical coupler 15 through the optical fiber 14. Optical fibers 16 and 17 are connected to the optical coupler 15. An optical coupler 18 is further connected to the optical fiber 17, and optical fibers 19 and 20 are further connected to the optical coupler 18. In this way, the optical couplers are connected one after another, and the light from the wavelength tunable laser 11 is branched. Here, the optical fibers 12, 14, 16, 17, 19, 20 and the optical fiber couplers 13, 15, 18 branch the laser light from the wavelength tunable laser and guide it to a plurality of sensor units, and the reflected light from each sensor unit The optical branching / synthesizing unit for synthesizing is configured.

  And sensor part S1, S2 ... Sn is provided in the edge part of each last optical fiber. For example, in the sensor unit S1 at the end of the optical fiber 16, a collimating lens 21 is provided, and a half mirror 22 and a reflecting plate 23 are provided perpendicular to the optical axis of the emitted light. The half mirror 22 reflects a part of incident light. The reflection plate 23 is displaced in the direction of the optical axis by external vibration, totally reflects the light transmitted through the half mirror 22, and is an element that detects vibration perpendicular to the surface. When the reflection plate 23 vibrates due to sound or vibration from a vibration source, for example, a sound source, the position of reflection is different. As a result, the interference wave varies with the half mirror 22. Similarly, for the sensor unit S2, a collimator lens 24, a half mirror 25, and a reflection plate 26 are provided at the other end of the optical fiber 19. A collimator lens 27, a half mirror 28, and a diaphragm 29 are also provided in the sensor portion Sn provided at the end of the optical fiber 20. The same applies to other sensor units (not shown). Here, the reflectors are arranged such that the distances L1, L2,... Ln between the half mirrors 22, 25, and 28 and the corresponding reflectors 23, 26, and 29 are different from each other. The reference position of the reflector is used. In this embodiment, light is caused to interfere with each sensor unit.

  Now, part of the reflected light obtained by the optical coupler 13 is guided to the optical fiber 31. A collimating lens 32 is provided at the end of the optical fiber 31, and a photodiode 33 as a light receiving element is provided on the optical axis thereof. The photodiode 33 converts the interference wave of the reflected light into an electric signal, and its output is given to the signal processing unit 35 via the amplifier 34.

  Next, the configuration within the signal processing unit 35 will be described. As shown in FIG. 2, the signal processing unit 35 converts an output from the photodiode 33 into a digital value, and converts the output of the A / D conversion unit 41 from a time domain signal to a frequency domain signal. It has a Fourier transform unit 42 for transforming. Furthermore, a frequency separation unit 43 that separates signals by frequency band out of Fourier-transformed frequency domain signals and a Fourier inverse transform unit 44 that performs Fourier inverse transform on the output thereof are provided. Further, a Fourier transform unit 45 for further Fourier transforming the inversely transformed output is configured.

  Next, the operation of the present embodiment will be described. The wavelength tunable laser 11 outputs a wavelength scanning signal having a wavelength band of 100 nm in a 1.5 μm band, for example. This scanning frequency is set to 50 kHz, for example. This light is given to the sensor units S1, S2,... Sn from the optical fibers 16, 19, and 20 via the optical fiber 12 and the optical couplers 13 and 15, respectively. In each sensor unit, light is emitted from the end of the sensor unit through the collimator lenses 22, 24, and 27 as parallel light, and part of the light is reflected by the half mirrors 22, 25, and 28. Part of the light passes through the half mirror and is reflected by the reflectors 23, 26 or 29. The half mirror 22 and the reflecting plate 23 constitute one etalon. The characteristics of the etalon of the sensor unit S1 are as shown in FIG. 3A, for example. Similarly, an etalon is constituted by the half mirror 25 and the reflection plate 26, and the intensity change with respect to the wavelength λ is as shown in FIG. 3B. The characteristics of the etalon constituted by the half mirror 22 and the reflection plate 29 are as shown in FIG. 3C. Here, since the distances L1, L2, and Ln between the respective half mirrors and the reflectors are gradually increased, the intervals of the intensity changes are shorter as the distances L1 to Ln are wider as shown in FIGS. 3A to 3C. It becomes.

  Since the single-mode light periodically swept in wavelength is incident on the etalon having such characteristics, the characteristics shown in FIGS. 3A to 3C are directly converted into signals whose intensity changes in the time axis region. The reflected light is superimposed via the optical couplers 18 and 15 and added to the optical coupler 13. Here, if the reflectors 22, 26, and 29 are moved by a vibration source at a minute interval perpendicular to the surface, each etalon is slightly cycled from the characteristics shown in FIGS. 3A, 3B, and 3C due to externally applied vibrations. Changes, and the level of the superimposed light is also in accordance therewith. The reflected light is emitted from the optical fiber 31 through the collimator lens 32 and converted into an electric signal by the photodiode 33. Then, it is converted into a digital value by the A / D converter 41 and further converted into a frequency domain signal by the Fourier transformer 42.

  FIG. 4 is a diagram showing the output of the Fourier transform unit 42. Here, if the reflectors 23, 26, and 29 are located at fixed positions with respect to the respective half mirrors 22, 25, and 28, the frequencies after Fourier transform are constant as f1, f2, and fn, respectively. Even if spike noise or the like is added here, it is converted into a signal in the frequency domain, so that such noise has a low level, and the frequency can be detected with a high S / N ratio. Each reflector 23, 26, 29 vibrates in the direction of the optical axis in the range of ΔL1, ΔL2,... ΔLn, so that the frequencies f1, f2,... Fn are also Δf1, Δf2,. ..Variable in the range of Δfn. Therefore, for example, with respect to the frequency f1, the frequency separation unit 43 detects the frequency band of only the change range Δf1, and the inverse Fourier transform unit 44 converts it to a time domain signal as shown in FIG. 5A. can do. In this case, the vertical axis is a signal indicating the vibration of the reflector 23 around the distance L1. If this signal is D / A converted and amplified, for example, and output from a speaker or the like, the sound obtained on the reflector 23 can be reproduced. Further, the time domain signal shown in FIG. 5A is further subjected to Fourier transform by the Fourier transform unit 45, whereby it can be converted into a frequency domain signal as shown in FIG. 6, and the spectrum at that time can be detected.

  Similarly, a signal in the change range Δf2 centered on the frequency f2 is extracted from the frequency domain signal shown in FIG. 4 by the frequency separation unit 43 and inverse Fourier transformed to obtain a time axis domain signal shown in FIG. 5B. If this is further subjected to Fourier transform by the Fourier transform unit 45, a signal in the frequency domain shown in FIG. 6B is obtained. Similarly, a time domain signal shown in FIG. 5C is obtained by extracting a frequency domain signal having a change range Δfn centered on the frequency fn and performing inverse Fourier transform. This is Fourier transformed to obtain a frequency domain signal shown in FIG. 6C.

  As described above, in the first embodiment, it is possible to detect multipoint vibrations of a large number of sensor units S1 to Sn, and to monitor a vibration source and analyze vibrations. Here, if the scanning speed of the wavelength tunable laser 11 is 40 kHz, it is possible to reproduce an audible acoustic signal in a band up to ½, that is, up to 20 kHz. It is also possible to analyze the vibrations of a plurality of vibration sources in real time. Further, by using a single mode light source with an infinite coherent length as the light source, the number of sensors can be increased almost infinitely. In addition, since minute light interference can be detected with respect to the etalon interference, an effect that the sensor unit is simplified can be obtained.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In this embodiment, only the sensor unit is different from the above-described first embodiment, and the other configurations are the same, and therefore the sensor unit S1 is shown in FIG. As shown in the figure, a half mirror 22 is provided behind the collimating lens 21 so that light is irradiated directly toward the vibration source 51 without using the reflector 23. Here, the distance between the half mirror 22 and the vibration source is set in advance to be a predetermined distance, for example, L1 in the sensor unit S1 and L2 in the sensor unit S2. The other sensor units are the same as those in the first embodiment. In this way, it is possible to detect and analyze the vibration state of the multi-point vibration source by causing the light to directly interfere with the reflected light from the vibration source without using a reflector.

(Embodiment 3)
Next, a third embodiment of the present invention will be described. Also in this embodiment, only the sensor unit is different from the above-described first embodiment, and other configurations are the same, and therefore the sensor unit S1 is shown in FIG. As shown in the figure, a beam splitter 52 is arranged at an angle of 45 ° with respect to the optical axis in place of the half mirror 22. The beam splitter 52 reflects a part of the signal light, for example 1/2, and transmits the other 1/2. The light reflected by the beam splitter 52 is guided to the mirror 53 as shown in the figure, and is reflected as it is and added to the original beam splitter 52. Accordingly, in this case, similarly to the half mirror, the light reflected by the beam splitter 52 and the reflected light from the reflecting portion 23 can be made to interfere with each other. Also in this case, it is necessary to keep the difference between the distance to the mirror 53 and the distance to the reflecting plate 23 from the position of the beam splitter 52 at a predetermined value L1. This difference is also set to L2, L3... For the other sensor units S2, S3. In this way, as in the first embodiment, it is possible to separately detect and analyze the vibration state of the reflecting part from each sensor part.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described. Also in this embodiment, only the sensor unit is different from that of the first embodiment described above, and other configurations are the same, and thus detailed description thereof is omitted. As shown in FIG. 9, the sensor unit S <b> 1 forms reference light by using a beam splitter 52 and a mirror 53, and directly irradiates light to the vibration source 51 except for the reflection unit 23, and reflects reflected light from the vibration source 51. It is designed to receive light. Also in this case, in the sensor unit S1, the difference between the distance to the mirror 53 and the distance from the vibration source 51 when viewed from the position of the beam splitter is set as a distance L1. This difference is also set to L2, L3... For the other sensor units S2, S3. In this way, the vibration state of the vibration source of each sensor unit can be separately detected and analyzed as in the first embodiment.

(Embodiment 5)
Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, the light from the wavelength tunable laser 11 is guided to the optical coupler 61 through the optical fiber 12. The optical coupler 61 couples an optical fiber 62 in addition to the optical fibers 12, 14, and 31, and branches the light of the wavelength tunable laser 11, and also interferes with reflected light and reference light as will be described later. Function as. The optical couplers 15 and 18 and the optical fibers 16, 17, and 20 that are branched portions after the optical fiber 14 are the same as those in the first embodiment. In each sensor part S1-Sn, except for the half mirrors 22, 25, 28, the parallel light from the collimating lenses 21, 24, 27 is directly applied to the reflecting plates 23, 26, 29. Each reflector is assumed to vibrate in the optical axis direction by minute distances ΔL1, ΔL2, and ΔLn by vibration.

  In the fifth embodiment, a collimator lens 63 and a reference mirror 64 are provided at the tip of the optical fiber 62. Here, the optical distance from the optical coupler 61 to the reference mirror 64 is L0. The distance from the optical coupler 61 to the reflection plate 23 is set to a value obtained by adding the distance L1 of the first embodiment to the optical distance L0, that is, L0 + L1. Similarly, in order to make the optical distance from the optical coupler 61 to the reflecting plate 26 the same as in the first embodiment, it is set to L0 + L2. Further, the optical distance from the optical coupler 61 to the reflecting plate 29 is set to L0 + Ln. In this way, in the sensor unit S1, the difference between the distance to the reference mirror 64 and the optical distance to the reflecting plate 23 is L1. Similarly, the difference between the sensor units S2 and Sn is L2 and Ln. In this way, the plurality of half mirrors 22, 25, and 28 of the first embodiment can be replaced with one reference mirror 64, and the reflected light from the reference mirror 64 and the reflected light from each sensor unit are separated by the optical coupler 61. Can interfere. In the fifth embodiment, since the number of half mirrors can be reduced, this embodiment is effective when the number of sensors increases.

  In this embodiment, the distance from the optical coupler 61 to the reflecting plate of each sensor unit is set as L0 + L1..., But the difference is L1, L0-L1, L0-L2,. You may set so that it may become L2 and Ln.

(Embodiment 6)
Next, Embodiment 6 of the present invention will be described with reference to FIG. In this embodiment, the light from the wavelength tunable laser 11 is guided to the optical coupler 71. The optical coupler 71 is an optical branching part that splits light, and the first and second branched lights are given to the optical fibers 72 and 73. The optical fiber 72 is provided with a circulator 74. The circulator 74 guides the light incident from the optical fiber 72 to the optical fiber 75, and gives the light incident from the optical fiber 75 to the circulator 74 to the optical fiber 76. A circulator 77 is provided at the other end of the optical fiber 76. The circulator 77 guides incident light from the optical fiber 76 to the optical fiber 78, and guides incident light from the optical fiber 78 to the circulator 77 to the optical fiber 79. In this way, light is branched by cascade-connecting circulators. A circulator 81 is also provided in the final stage optical fiber 80. Similarly, the circulator 81 guides the incident light from the optical fiber 80 to the optical fiber 82, and guides the light incident from the optical fiber 82 to the circulator 81 to the optical fiber 83. Here, the circulators 74, 77, and 81 and the optical fibers connected thereto constitute an optical circulator unit that divides the first branched light branched by the optical branching unit and synthesizes the reflected light. The other ends of the optical fibers 75, 78, and 82 are provided with sensor portions S1, S2, and Sn similar to those in the fifth embodiment.

  A circulator 84 is also provided at the other end of the optical fiber 73 branched by the optical coupler 71. The circulator 84 guides the light from the optical fiber 73 to the optical fiber 85 and guides the reflected light from the optical fiber 85 to the optical fiber 86. A collimating lens 87 and a reference mirror 88 are provided at the other end of the optical fiber 85. Here, an optical coupler 89 is provided at the other end of the optical fibers 83 and 86. The optical coupler 89 is an optical interference unit that extracts two interference waves whose phases are inverted by causing the reflected light from the optical fiber 83 and the reference light from the optical fiber 86 to interfere with each other. Two interference waves are guided to the balanced photodiode 90. The balanced photodiode 90 is a light receiving element that converts a difference value between two inputs into an electric signal. The output of the photodiode 90 is supplied to the signal processing unit 35 described above via the amplifier 34. The configuration of the signal processing unit 35 is the same as that of the first embodiment.

  In this embodiment, a Mach-Zehnder interferometer is used instead of a Michelson interferometer, and since an optical circulator is used, attenuation of the optical signal can be reduced as compared with the optical coupler described above. In this embodiment, two interference waves whose phases are inverted can be extracted from the optical coupler 89, and the difference between them is detected by the balanced photodiode 90, so that the signal level can be doubled. . Therefore, even if the output level of the wavelength tunable laser 11 is low, it can be used for a multi-point type detection system having a large number of sensor units, and an excellent effect that vibrations of each sensor unit can be detected with high sensitivity is obtained. It is done.

  In this embodiment, each sensor unit applies the output from the collimating lens to the reflecting plates 23, 26, and 29 whose positions on the optical axis vibrate due to external vibration, but as in the second embodiment. The reflected light may be received by directly irradiating the vibration source with the light branched off. In this embodiment, the reference light generated by the reference mirror unit and the reflected light superimposed from the optical circulator unit are interfered by using an optical coupler, but a beam splitter or the like is used instead of the optical coupler. You can also

It is a block diagram which shows the structure of the optical fiber sensor system by Embodiment 1 of this invention. It is a figure which shows the structure of the signal processing part of this Embodiment. It is a figure which shows the wavelength of etalon and signal strength in sensor part S1. It is a figure which shows the wavelength of etalon and signal strength in sensor part S2. It is a figure which shows the wavelength and signal intensity | strength of an etalon in sensor part Sn. It is a figure which shows the signal of the reflected light superimposed on an optical fiber. It is a figure which shows the vibration of sensor part S1 which is isolate | separated by a frequency separation part and is obtained by carrying out Fourier inverse transform. It is a figure which shows the vibration of sensor part S2 which is isolate | separated by a frequency separation part and is obtained by carrying out Fourier inverse transform. It is a figure which shows the vibration of the sensor part Sn isolate | separated by a frequency separation part and obtained by carrying out Fourier inverse transform. It is the figure which converted the signal of the time-axis direction of sensor part S1 into the frequency axis. It is the figure which converted the signal of the time-axis direction of sensor part S2 into the frequency axis. It is the figure which converted the signal of the time-axis direction of the sensor part Sn into the frequency axis. It is a block diagram which shows the structure of the sensor part by Embodiment 2 of this invention. It is a block diagram which shows the structure of the sensor part by Embodiment 3 of this invention. It is a block diagram which shows the structure of the sensor part by Embodiment 4 of this invention. It is a block diagram which shows the structure of the optical fiber sensor system by Embodiment 5 of this invention. It is a block diagram which shows the structure of the optical fiber sensor system by Embodiment 6 of this invention.

Explanation of symbols

11 wavelength tunable laser 12, 14, 16, 17, 19, 20, 62, 72, 73, 75, 76, 78, 79, 80, 82, 83 optical fiber 13, 15, 18, 71, 89 optical coupler 21, 24, 27, 63, 87 Collimating lens 22, 25, 28 Half mirror 23, 26, 29 Reflector S1, S2,... Sn sensor unit 33 Photo diode 34 Amplifier 35 Signal processing unit 41 A / D conversion unit 42 Fourier transform Unit 43 frequency separation unit 44 inverse Fourier transform unit 45 Fourier transform unit 51 vibration source 52 beam splitter 53 mirror 64 reference mirror 74, 77, 81, 84 optical circulator 90 balanced photodiode

Claims (7)

A tunable laser that generates single-mode light whose wavelength periodically changes in a certain wavelength range;
An optical branching unit for branching light from the wavelength tunable laser into first and second branched light;
An optical circulator unit that divides the first branched light branched by the optical branching unit by a plurality of optical circulators cascaded via an optical fiber, and synthesizes the reflected light;
An optical circulator that further branches the second branched light of the optical branching section, a reference mirror that reflects light obtained from the optical circulator, and a reference mirror section that generates reference light;
A plurality of sensors to which the branched light beams separated by the optical circulator unit are respectively given, set different reflection reference positions, generate reflected light whose respective reflection positions change due to vibration applied from the outside, and return them to the optical circulator unit And
An optical interference unit that causes interference between the reflected light signal superimposed from the optical circulator unit and the reference light generated by the reference mirror unit;
A light receiving unit that photoelectrically converts a difference between two interference waves whose phases are inverted from each other obtained from the optical interference unit;
A Fourier transform unit that converts a received light signal obtained by the light receiving unit into a frequency domain signal by Fourier transform;
A frequency separation unit for separating the Fourier-transformed signal in a frequency domain and extracting the Fourier transform signal corresponding to the signal from each sensor unit;
An optical fiber sensor system comprising: a Fourier inverse transform unit that inversely transforms a signal from each sensor unit separated by the frequency separation unit into a time domain signal.   The optical fiber sensor system according to claim 1, wherein each of the sensor units irradiates a branching light to a vibration source to be measured and receives the reflected light. A tunable laser that generates single-mode light whose wavelength periodically changes in a certain wavelength range;
An optical branching / synthesizing unit that includes an optical fiber to which light from the wavelength tunable laser is applied and an optical coupler for branching and coupling the light, and divides the laser light from the wavelength tunable laser into a plurality of parts and combines reflected light When,
The light branched from the light branching / synthesizing unit is given, branches the light, sets different reflection reference positions, and interferes with the reflected light whose reflection position changes due to vibration applied from the outside, thereby interfering light. A plurality of sensor units for guiding the light to the optical branching and combining unit;
A light receiving unit that receives the interference light combined from the light branching and combining unit and converts it into an electrical signal;
A Fourier transform unit that converts a received light signal obtained by the light receiving unit into a frequency domain signal by Fourier transform;
A frequency separation unit for separating the Fourier-transformed signal in a frequency domain and extracting the Fourier transform signal corresponding to the signal from each sensor unit;
An optical fiber sensor system comprising: a Fourier inverse transform unit that inversely transforms a signal from each sensor unit separated by the frequency separation unit into a signal in a time domain.   The optical fiber sensor system according to claim 3, wherein each of the sensor units irradiates a vibration source to be measured with a branched light and receives the reflected light.   The sensor unit includes a beam splitter disposed at an angle of 45 ° with respect to the optical axis, and a mirror that reflects the light branched from the beam splitter and returns the light to the beam splitter. The optical fiber sensor system of Claim 3 or 4 to produce | generate. A tunable laser that generates single-mode light whose wavelength periodically changes in a certain wavelength range;
An optical fiber to which light from the wavelength tunable laser is applied and an optical coupler for branching and coupling the light; and a light branching and combining unit for branching the laser light from the wavelength tunable laser and combining reflected light;
Each of the branched light beams from the light branching and combining unit is given, and a plurality of reflection reference positions are set, and a plurality of reflected lights whose reflection positions are changed by vibration applied from the outside are guided to the light branching and combining unit. A sensor unit;
A reference reflection unit connected to the optical branching and combining unit, for changing the branched light from the wavelength tunable laser at a reference reflection position and guiding the reference light to the optical fiber of the branching and combining unit;
A light interference unit that causes interference between reflected light obtained from the light branching and combining unit and reference light obtained from the reference reflecting unit;
A light receiving unit that receives interference light obtained from the light interference unit and converts it into an electrical signal;
A Fourier transform unit that transforms a received light signal obtained in the light receiving unit into a frequency domain signal by Fourier transform;
A frequency separation unit for separating the Fourier-transformed signal in a frequency domain and extracting the Fourier transform signal corresponding to the signal from each sensor unit;
An optical fiber sensor system comprising: a Fourier inverse transform unit that inversely transforms a signal from each sensor unit separated by the frequency separation unit into a time domain signal.   The optical fiber sensor system according to claim 6, wherein each of the sensor units irradiates the vibration source to be measured with the branched light and receives the reflected light.

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