JP6350239B2 - Interference type optical fiber sensor system and interference type optical fiber sensor head - Google Patents

Description

  The present invention relates to an interference optical fiber sensor system and an interference optical fiber sensor head.

  Patent Document 1 describes an interference type optical fiber sensor including a sensing arm and a reference arm. The sensing arm and the reference arm are provided with a temperature compensating fiber for suppressing temperature drift. Patent Document 2 describes an interference type optical fiber sensor including a first optical fiber coil and a second optical fiber coil. In this interference type optical fiber sensor, the first optical fiber coil and the second optical fiber coil are wound around a common coil. This coil has a shape capable of sandwiching a permanent magnet.

JP 2005-241298 A Japanese Patent No. 3107986

  In the interference type optical fiber sensor described in Patent Document 1, since a special fiber is used as a temperature compensating fiber, there is a concern about an increase in manufacturing costs. In the interference type optical fiber sensor described in Patent Document 2, it is necessary to prepare a coil having a special shape and the first and second optical fiber coils wound thereon and a permanent magnet. Therefore, there is a problem that the number of parts is large and the configuration is complicated. Further, in the interference type optical fiber sensor as described above, it is desired to suppress the influence of the environment as much as possible in order to surely measure the modulation of the measurement light and the reference light.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an interference type optical fiber sensor system and an interference type optical fiber sensor head capable of reducing the influence of the environment with a simple configuration.

  In order to solve the above-described problem, an interference-type optical fiber sensor system according to one aspect of the present invention includes a light source, a first coupler optically connected to the light source, and an optical connection to the first coupler. A first optical path for inputting one of the measurement light and the reference light branched from the first coupler; a second optical path optically connected to the first coupler for inputting the other of the measurement light and the reference light; A second coupler that couples the first optical path and the second optical path, a measurement unit that measures the modulation of the measurement light and the reference light based on the light coupled by the second coupler, and the measurement light and the measurement light by the applied stress A modulation unit that modulates the reference light, wherein the optical length in the first optical path and the optical length in the second optical path are equal to each other, and the modulation unit includes the first optical path and the second optical path wound around a common core. A coil that includes an optical path and is applied to the coil. The modulation timing given to one of the measurement light and the reference light is different from the modulation timing given to the other, and the measurement unit is configured to transmit interference light from the measurement light and the reference light modulated by the modulation unit. Measure intensity fluctuations.

  An interference-type optical fiber sensor system according to another aspect of the present invention includes a light source, a coupler optically connected to the light source and having two branch ends, one end connected to one branch end of the coupler, and the other end Is connected to the other branch end of the coupler, the optical path for inputting the signal light output from the coupler, the measurement unit for measuring the modulation of the signal light based on the light coupled by the coupler, and the applied stress And a modulation unit that modulates the signal light by a coil including an optical path, and the optical path is different from the first winding unit wound around the core of the coil and the first winding unit. A second winding part wound around a core at a location, and a modulation timing given to the signal light passing through the first winding part and a modulation timing given to the signal light passing through the second winding part are: They are different from each other.

  An interference type optical fiber sensor head according to one aspect of the present invention includes a coupler having an input end, an output end, and two branch ends, one end connected to one of the two branch ends, and the other end having two branches. An optical path connected to the other end of the coil, and a coil around which the optical path is wound. The optical path has a first winding portion wound around the core of the coil and a core at a location different from the first winding portion. A second winding portion wound around the first winding portion and a loop portion provided between the first winding portion and the second winding portion, and is given to light passing through the first winding portion by stress applied to the coil. The modulation timing is different from the modulation timing applied to the light passing through the second winding portion due to the stress.

  Furthermore, an interference type optical fiber sensor head according to another aspect of the present invention includes a first coupler having an input end, an output end, and two branch ends, and a second coupler having an input end, an output end, and two branch ends. A third optical path having one end connected to one branch end of the first coupler and the other end connected to the input end of the second coupler; one end connected to the other branch end of the first coupler; A fourth optical path whose end is connected to the output end of the second coupler, a loop-shaped fifth optical path extending from one branch end of the second coupler to the other branch end, a third optical path, and a fourth optical path. A coil wound with an optical path, and a modulation timing applied to light passing through the third optical path by stress applied to the coil, and a modulation timing applied to light passing through the fourth optical path by stress Are different from each other.

  According to the present invention, the influence of the environment can be reduced with a simple configuration.

FIG. 1 is a diagram showing an interference type optical fiber sensor system according to the first embodiment. FIG. 2 is a diagram showing an interference type optical fiber sensor system according to the second embodiment. FIG. 3 is a diagram showing an interference type optical fiber sensor system according to the third embodiment. FIG. 4 is a diagram showing an interference type optical fiber sensor system according to the fourth embodiment.

[Description of Embodiment of the Present Invention]
First, the contents of the embodiment of the present invention will be listed and described. (1) An interference type optical fiber sensor system according to one aspect of the present invention includes a light source, a first coupler optically connected to the light source, an optical connection to the first coupler, and a branch from the first coupler. A first optical path for inputting one of the measurement light and the reference light, a second optical path optically connected to the first coupler and inputting the other of the measurement light and the reference light, a first optical path, and a second optical path. A second coupler that couples the optical paths, a measurement unit that measures the modulation of the measurement light and the reference light based on the light coupled by the second coupler, and a modulation that modulates the measurement light and the reference light by the applied stress And the optical length in the first optical path and the optical length in the second optical path are equal to each other, and the modulation unit is a coil including the first optical path and the second optical path wound around a common core. Yes, measurement light and reference depending on the stress applied to the coil While the timing of the modulation applied to the the timing of the modulation applied to the other, they are different from each other, the measurement unit measures the intensity variation of the interference light by measurement light and reference light modulated by the modulation unit.

  In the interference type optical fiber sensor system according to one aspect of the present invention, when stress is applied to the coil, the measurement light and the reference light are modulated. The modulation timing given to one of the measurement light and the reference light is different from the modulation timing given to the other, and one of the modulated measurement light and reference light is delayed from the other. Therefore, the measurement unit can selectively extract the measurement light and the reference light. Therefore, the influence by the environment can be reduced with a simple configuration, and the measurement unit can reliably measure the modulation of the measurement light and the reference light.

  (2) In the interference optical fiber sensor system described above, the path through which the light output from the second coupler passes may be a loop extending from the second coupler and returning to the second coupler. As a result, the number of optical paths through which the light output from the second coupler passes can be reduced, which contributes to a reduction in the number of components.

  (3) In the interference optical fiber sensor system, a delay line may be provided in at least one of the first optical path and the second optical path. Thereby, the measurement part can measure modulation of measurement light and reference light more certainly.

  (4) An interference optical fiber sensor system according to another aspect of the present invention includes a light source, a coupler optically connected to the light source and having two branch ends, and one end connected to one branch end of the coupler. An optical path through which the other end is connected to the other branch end of the coupler and the signal light output from the coupler is input, a measurement unit that measures the modulation of the signal light based on the light coupled by the coupler, and A modulation unit that modulates the signal light by the applied stress, and the modulation unit is a coil including an optical path, and the optical path includes a first winding unit wound around the core of the coil, and a first winding unit. Has a second winding part wound around the core at another location, and a modulation timing given to the signal light passing through the first winding part and a modulation timing given to the signal light passing through the second winding part Are different from each other.

  In the interference type optical fiber sensor system according to another aspect of the present invention, the signal light is modulated when stress is applied to the coil. The modulation timing given to the signal light passing through the first winding unit and the modulation timing given to the signal light passing through the second winding unit are different from each other, and one of the first winding unit and the second winding unit is used. The signal light passing through is delayed more than the signal light passing through the other. Therefore, similarly to the above-described interference type optical fiber sensor system, the influence of the environment can be reduced with a simple configuration. Furthermore, in this interference type optical fiber sensor system, since the optical path can be configured by a single path, the number of parts can be reduced.

  (5) In the interference type optical fiber sensor system described above, the light branching ratio in the coupler may be a: 1 (where a is a positive real number that is not 1). Thus, the interference type optical fiber sensor system can be configured in such a manner that light is transmitted through the coupler, and the modulation units can be easily connected in cascade.

  (6) In the interference type optical fiber sensor system, the stress may propagate as an acoustic wave.

  (7) An interference type optical fiber sensor head according to one aspect of the present invention includes a coupler having an input end, an output end, and two branch ends, one end connected to one of the two branch ends, and two other ends. An optical path connected to the other of the branch ends, and a coil around which the optical path is wound. The optical path is different from the first winding part and the first winding part wound around the core of the coil. A second winding portion wound around the core, and a loop portion provided between the first winding portion and the second winding portion, and applied to the light passing through the first winding portion by stress applied to the coil. The modulation timing applied is different from the modulation timing applied to the light passing through the second winding portion due to the stress. In this interference type optical fiber sensor head, the optical path in the modulation section can be made one, and the number of parts can be reduced.

  (8) An interference type optical fiber sensor head according to another aspect of the present invention includes a first coupler having an input end, an output end, and two branch ends, and a second coupler having an input end, an output end, and two branch ends. A coupler, one end connected to one branch end of the first coupler, the other end connected to the input end of the second coupler, and one end connected to the other branch end of the first coupler; A fourth optical path having the other end connected to the output end of the second coupler, a loop-shaped fifth optical path extending from one branch end of the second coupler to the other branch end, a third optical path, A coil wound with four optical paths, and a modulation timing given to light passing through the third optical path by a stress applied to the coil, and a modulation timing given to light passing through the fourth optical path by the stress Are different from each other. In this interference type optical fiber sensor head, the fifth optical path extending from the second coupler has a loop shape. Therefore, the number of optical paths through which the light output from the second coupler passes can be reduced, which contributes to a reduction in the number of components.

[Details of the embodiment of the present invention]
Specific examples of an interference optical fiber sensor system and an interference optical fiber sensor head according to an embodiment of the present invention will be described with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the range equivalent to a claim are included. In the following description, the same reference numerals are given to the same elements in the description of the drawings, and redundant descriptions are omitted.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of an interference optical fiber sensor system 1 according to the first embodiment. As shown in FIG. 1, the interference type optical fiber sensor system 1 includes a light source 11, a first coupler 12, a first optical path 13, a second optical path 14, a second coupler 18, and a photodetector. 19 and a coil (modulation unit) 20. The interference type optical fiber sensor system 1 constitutes a Mach-Zehnder type interferometer.

  The light source 11 outputs signal light L1 that is pulsed light. The light source 11 is optically connected to the first coupler 12. The first coupler 12 is, for example, a 3 dB coupler. The first coupler 12 has an input end 12a, an output end 12b, and two branch ends 12c and 12d. The signal light L1 output from the light source 11 is input to the input terminal 12a of the first coupler 12. The branching ratio in the first coupler 12 is, for example, 1: 1. The first coupler 12 branches the signal light L1 from the light source 11 into measurement light L2 that is pulsed light and reference light L3 that is pulsed light. The first coupler 12 outputs the measurement light L2 from the branch end 12c and outputs the reference light L3 from the branch end 12d.

  The first optical path 13 is optically connected to the branch end 12 c of the first coupler 12. The first optical path 13 inputs the measurement light L2 branched from the first coupler 12. One end of the first optical path 13 is connected to the first coupler 12, and the other end of the first optical path 13 is connected to the second coupler 18. The first optical path 13 inputs the measurement light L2 output from the first coupler 12 to one end of the first optical path 13 and guides it. A coil 20 is disposed in the middle of the first optical path 13.

  The second optical path 14 is optically connected to the branch end 12 d of the first coupler 12. The second optical path 14 inputs the reference light L3 branched from the first coupler 12. One end of the second optical path 14 is connected to the first coupler 12, and the other end of the second optical path 14 is connected to the second coupler 18. The second optical path 14 guides the reference light L3 output from the first coupler 12 by inputting it to one end of the second optical path 14. A coil 20 is disposed in the middle of the second optical path 14. The optical length in the second optical path 14 is equal to the optical length in the first optical path 13. The materials of the first optical path 13 and the second optical path 14 are the same as each other, for example.

  The coil 20 has a core 17 around which the first optical path 13 and the second optical path 14 are wound. The length and the number of turns of the first optical path 13 wound around the core 17 of the coil 20 are, for example, the same as the length and the number of turns of the second optical path 14 wound around the core 17. The first optical path 13 and the second optical path 14 are wound with a predetermined distance H from each other. Further, stress is applied to the coil 20 by receiving vibration or the like from the outside. The stress in the coil 20 propagates as an acoustic wave, for example.

If the distance the distance H between the first optical path 13 on the coil 20 and the second optical path 14, the velocity of the propagating stress was v _s, the stress is propagated from the second optical path 14 to the first optical path 13 time t is the H / _{v s.} Here, the modulation timing given to the measurement light L2 by the stress applied to the coil 20 is different from the modulation timing given to the reference light L3. That is, for example, when stress is applied to the coil 20 from the second optical path 14 side, the stress is propagated to the first optical path 13 with a delay of time t from the second optical path 14. Therefore, the time t, which is the difference between the time during which the stress is propagated in the first optical path 13 and the time during which the stress is propagated in the second optical path 14, can be used as the delay time.

  The second coupler 18 couples the first optical path 13 and the second optical path 14. The second coupler 18 couples the measurement light L2 that has passed through the first optical path 13 and the reference light L3 that has passed through the second optical path 14. The second coupler 18 is optically connected to the photodetector 19. The light coupled by the second coupler 18 is output to the photodetector 19.

  The photodetector 19 detects the modulation of the measurement light L2 and the reference light L3 based on the light coupled by the second coupler 18. The photodetector 19 receives the interference light between the measurement light L2 and the reference light L3. The photodetector 19 performs homodyne detection for detecting the interference light. In a state where no stress is generated in the coil 20, the measurement light L2 and the reference light L3 are simultaneously input to the second coupler 18. Therefore, the photodetector 19 measures the interference light of the measurement light L2 that is not given a delay and the reference light L3 that is not given a delay.

  On the other hand, when a stress is generated in the coil 20, phase modulation occurs in the measurement light L2 and the reference light L3 in the coil 20 due to this stress. Specifically, for example, when stress is applied to the coil 20 from the second optical path 14 side, the stress is propagated to the first optical path 13 after a time t from the second optical path 14. Therefore, a phase difference occurs between the measurement light L2 passing through the first optical path 13 and the reference light L3 passing through the second optical path 14, and the branching ratio of the second coupler 18 changes based on this phase difference. . The photodetector 19 detects a change in the branching ratio in the second coupler 18. The photodetector 19 measures the intensity fluctuation of the interference light caused by the measurement light L2 and the reference light L3. Then, the interference type optical fiber sensor system 1 detects that a stress is applied to the coil 20.

  The effect obtained by the interference type optical fiber sensor system 1 having the above configuration will be described.

  In the interference type optical fiber sensor system 1, when stress is applied to the coil 20, the measurement light L2 and the reference light L3 are modulated. The timing of modulation given to the measurement light L2 and the timing of modulation given to the reference light L3 are different from each other. For example, the modulated measurement light L2 is delayed from the modulated reference light L3. Therefore, the photodetector 19 can selectively extract the measurement light L2 and the reference light L3. Therefore, the influence by the environment can be reduced with a simple configuration, and the photodetector 19 can reliably measure the modulation of the measurement light L2 and the reference light L3.

(Second Embodiment)
FIG. 2 is a diagram illustrating a configuration of an interference optical fiber sensor system 1A according to the second embodiment. In the second embodiment, descriptions overlapping with those in the first embodiment are omitted. In the third and fourth embodiments, which will be described later, a duplicate description is omitted. As shown in FIG. 2, the interference type optical fiber sensor system 1 </ b> A includes an apparatus main body 2 and two interference type optical fiber sensor heads 3. The number of interference type optical fiber sensor heads 3 is not limited to two, and may be one or three or more. The apparatus main body 2 includes a light source 11 and a photodetector 19. The interference type optical fiber sensor head 3 includes a coupler 22, an optical path 23, and a coil 20.

  The coupler 22 includes an input end 22a that receives the signal light L4, an output end 22b that outputs the signal light L4, and two branch ends 22c and 22d that output the branched signal light L4. One branch end 22c is connected to one end of the optical path 23, and the other branch end 22d is connected to the other end of the optical path 23. The optical path 23 includes a first winding portion 23a wound around the core 17 of the coil 20, a second winding portion 23b wound around the core 17 at a location different from the first winding portion 23a, and a first winding portion 23a. And a loop portion 23c provided between the second winding portion 23b.

  Here, when the branching ratio in the coupler 22 is a: 1 (a is a positive real number), the value of a is other than 1, and preferably 100 or more. That is, the branching ratio of the signal light L4 in the coupler 22 is a branching ratio other than 1: 1, and the amount of the signal light L4 from the branching end 22c is different from the amount of the signal light L4 from the branching end 22d. For example, when the ratio of the signal light L4 from the branch end 22c and the signal light L4 from the branch end 22d is 100: 1, the signal light L4 output from the branch end 22d is output from the branch end 22c. The amount of signal light L4 to be increased 100 times. At this time, the signal light L4 from the branch end 22c passes through the first winding portion 23a, the loop portion 23c, and the second winding portion 23b in this order and is input to the branch end 22d. The signal light L4 is output from the output end 22b to the input end 22a of another coupler 22. In this way, the interference type optical fiber sensor system 1A can be configured as a so-called transmission type because the coupler 22 transmits the signal light L4.

  As described above, in the interference type optical fiber sensor system 1A, the signal light L4 is modulated when a stress is applied to the coil 20, as in the first embodiment. The timing of modulation applied to the signal light L4 passing through the first winding unit 23a is different from the timing of modulation applied to the signal light L4 passing through the second winding unit 23b. That is, the signal light L4 passing through one of the first winding part 23a and the second winding part 23b is delayed from the signal light L4 passing through the other. Therefore, similarly to the interference type optical fiber sensor system 1 of the first embodiment, the influence of the environment can be reduced with a simple configuration. Furthermore, in the interference type optical fiber sensor system 1A, since the optical path 23 is a single path, the number of parts can be reduced as compared with the interference type optical fiber sensor system 1.

  In the interference type optical fiber sensor system 1A, the light branching ratio in the coupler 22 is a: 1 (where a is a positive real number other than 1). Therefore, the interference type optical fiber sensor system 1A can be configured in such a manner that light is transmitted through the coupler 22, and the cascade connection of the interference type optical fiber sensor head 3 (coil 20) can be easily performed.

(Third embodiment)

  FIG. 3 is a diagram illustrating a configuration of an interference optical fiber sensor system 1B according to the third embodiment. As shown in FIG. 3, the interference optical fiber sensor system 1B includes an apparatus main body 2 and an interference optical fiber sensor head 3A. In FIG. 3, only one interference type optical fiber sensor head 3 </ b> A is illustrated. However, for example, by connecting the output end 32 b of the first coupler 32 to the input end 32 a of another first coupler 32, It is also possible to connect a plurality of interference type optical fiber sensor heads 3A in cascade.

  The interference type optical fiber sensor head 3A includes a first coupler 32, a third optical path 33, a fourth optical path 34, a fifth optical path 35, and a second coupler 38. One end of the third optical path 33 is connected to the first coupler 32, and the other end of the third optical path 33 is connected to the second coupler 38. The third optical path 33 includes a first winding portion 36 that is wound around the core 17 of the coil 20 in the middle of the third optical path 33. The fourth optical path 34 has a second winding part 37 wound around the core 17 in the middle of the fourth optical path 34. Further, the fifth optical path 35 extends from the second coupler 38 in a loop shape.

  The first coupler 32 has an input end 32a that receives the signal light L5, an output end 32b that outputs the signal light L5, and two branch ends 32c and 32d that output the branched signal light L5. The branching ratio of the first coupler 32 is, for example, 1: 1. Similar to the first coupler 32, the second coupler 38 has an input end 38a, an output end 38b, and two branch ends 38c and 38d. One branch end 38c is connected to one end of the fifth optical path 35, and the other branch end 38d is connected to the other end of the fifth optical path 35.

  As described above, in the interference-type optical fiber sensor system 1B, the modulation timing given to the signal light L5 passing through the first winding unit 36 and the modulation timing given to the signal light L5 passing through the second winding unit 37 are different from each other. . Therefore, in the interference type optical fiber sensor system 1B, the same effect as the interference type optical fiber sensor systems 1 and 1A can be obtained.

  Further, in the interference optical fiber sensor system 1B, the fifth optical path 35 has a loop shape extending from the second coupler 38 and returning to the second coupler 38. Therefore, the number of optical paths through which the signal light L5 output from the second coupler 38 passes can be reduced, which contributes to a reduction in the number of components.

(Fourth embodiment)
FIG. 4 is a diagram illustrating a configuration of an interference optical fiber sensor system 1C according to the fourth embodiment. The interference type optical fiber sensor system 1C constitutes a Michelson type interferometer. The interference optical fiber sensor system 1 </ b> C includes a mirror 26 provided at the output end of the first optical path 13 and a mirror 27 provided at the output end of the second optical path 14. The difference between the optical length in the first optical path 13 and the optical length in the second optical path 14 is, for example, (4n ± 1) λ / 4 (where n is an integer and λ is the wavelength of the signal light L1). In this interference type optical fiber sensor system 1C, the same effects as those of the interference type optical fiber sensor systems 1, 1A, 1B can be obtained.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. For example, in the interference optical fiber sensor system 1 or the interference optical fiber sensor system 1C, a delay line may be provided in at least one of the first optical path 13 and the second optical path 14. By providing the delay line in this way, the photodetector 19 can more reliably measure the modulation of the measurement light L2 and the reference light L3. The same effect can be obtained when a delay line is provided in the optical path 23 of the interference type optical fiber sensor system 1A or the third optical path 33 or the fourth optical path 34 of the interference type optical fiber sensor system 1B. .

  In the above-described embodiment, the first optical path 13 has been described as receiving the measurement light L2 branched from the first coupler 12. However, the present invention is not limited to this. Reference light may be input to the first optical path 13 and measurement light may be input to the second optical path 14.

DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C ... Interference type optical fiber sensor system, 2 ... Apparatus main body, 3, 3A ... Interference type optical fiber sensor head, 11 ... Light source, 12, 32 ... 1st coupler, 13 ... 1st optical path, DESCRIPTION OF SYMBOLS 14 ... 2nd optical path, 17 ... Core, 18, 38 ... 2nd coupler, 19 ... Photo detector (measurement part), 20 ... Coil (modulation part), 22 ... Coupler, 23 ... Optical path, 23a ... 1st Winding part, 23b ... second winding part, 23c ... loop part, 33 ... third optical path, 34 ... fourth optical path, 35 ... fifth optical path, 36 ... first winding part, 37 ... second winding part, H ... interval, L1, L4, L5 ... signal light, L2 ... measurement light, L3 ... reference light.

Claims (8)

A light source;
A first coupler optically connected to the light source;
A first optical path optically connected to the first coupler and receiving one of the measurement light and the reference light branched from the first coupler;
A second optical path optically connected to the first coupler for inputting the other of the measurement light and the reference light;
A second coupler for coupling the first optical path and the second optical path;
A measurement unit that measures the modulation of the measurement light and the reference light based on the light coupled by the second coupler;
A modulation unit that modulates the measurement light and the reference light by applied stress, and
The optical length in the first optical path and the optical length in the second optical path are equal to each other,
The modulation unit is a coil including the first optical path and the second optical path wound around a common core,
The modulation timing given to one of the measurement light and the reference light by the stress applied to the coil is different from the modulation timing given to the other,
The measurement unit measures intensity fluctuations of interference light caused by the measurement light and the reference light modulated by the modulation unit;
Interferometric optical fiber sensor system. The path through which the light output from the second coupler passes has a loop shape extending from the second coupler and returning to the second coupler.
The interference type optical fiber sensor system according to claim 1. A delay line is provided in at least one of the first optical path and the second optical path;
The interference type optical fiber sensor system according to claim 1. A light source;
A coupler optically connected to the light source and having two branch ends;
One end is connected to one branch end of the coupler, the other end is connected to the other branch end of the coupler, and an optical path for inputting the signal light output from the coupler;
A measurement unit for measuring the modulation of the signal light based on the light coupled by the coupler;
A modulation unit that modulates the signal light by the applied stress,
The modulation unit is a coil including the optical path,
The optical path has a first winding part wound around the core of the coil, and a second winding part wound around the core at a location different from the first winding part,
The modulation timing given to the signal light passing through the first winding unit and the modulation timing given to the signal light passing through the second winding unit are different from each other,
Interferometric optical fiber sensor system. The light branching ratio in the coupler is a: 1.
The interference-type optical fiber sensor system according to claim 4.
However, a is a positive real number that is not 1. The stress propagates as an acoustic wave,
The interference type optical fiber sensor system according to any one of claims 1 to 5. A coupler having an input end, an output end and two branch ends;
An optical path having one end connected to one of the two branch ends and the other end connected to the other of the two branch ends;
A coil around which the optical path is wound,
The optical path includes a first winding portion wound around the core of the coil, a second winding portion wound around the core at a location different from the first winding portion, the first winding portion, and the first winding portion. A loop portion provided between the two winding portions,
The modulation timing given to the light passing through the first winding portion by the stress applied to the coil and the modulation timing given to the light passing through the second winding portion by the stress are different from each other.
Interferometric optical fiber sensor head. A first coupler having an input end, an output end and two branch ends;
A second coupler having an input end, an output end and two branch ends;
A third optical path having one end connected to one of the branch ends of the first coupler and the other end connected to the input end of the second coupler;
A fourth optical path having one end connected to the other branch end of the first coupler and the other end connected to the output end of the second coupler;
A loop-shaped fifth optical path extending from one branch end of the second coupler to the other branch end;
A coil around which the third optical path and the fourth optical path are wound,
The modulation timing given to the light passing through the third optical path by the stress applied to the coil is different from the modulation timing given to the light passing through the fourth optical path by the stress,
Interferometric optical fiber sensor head.

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