Fiber-optic pressure sensor and fiber-optic pressure measuring instrument

Abstract

Provided are a fiber-optic pressure sensor and a fiber-optic pressure measuring instrument which are capable of achieving cost reduction and / or high sensitivity. The present invention pertains to: a fiber-optic pressure sensor 1 for detecting pressure on one end side of an optical fiber 10; and a fiber-optic pressure measuring instrument including the same. The fiber-optic pressure sensor comprises: the optical fiber 10; a tubular part 20 into which said one end side of the optical fiber 10 is inserted from one opening and fixed; a pressure sensitive part 30 that comprises a reflection surface 33 disposed to face an end section 11 on said one end side of the optical fiber 10 and a pressure receiving surface 34 oriented opposite to the reflection surface 33 and facing the other opening of the tubular part 20, and that can move in the axial direction in the tubular part 20; and an elastic body 40 that is interposed between the tubular part 20 and the pressure sensitive part 30, and in which repulsive force acts on movement in the direction in which the pressure sensitive part 30 approaches the end section 11 on said one end side of the optical fiber 10.

Description

Optical fiber pressure sensor and optical fiber pressure measuring instrument

[0001] The present invention relates to an optical fiber pressure sensor and an optical fiber pressure measuring instrument.

[0002] Optical fiber pressure sensors have been proposed for measuring the pressure inside a fine tube, etc. For example, Patent Document 1 discloses a force sensor in which a diaphragm that bends when pressure is applied serves as a pressure-receiving surface, and the sensor measures pressure changes by optically detecting and analyzing the optical path difference of reflected light of light irradiated from an optical fiber as the movement of a total reflection mirror fixed to the pressure-receiving surface.

[0003] In the technology described in Patent Document 1, the range of movement of the total reflection mirror that moves due to pressure is extremely small due to the shape deformation of the diaphragm, and is on the order of the wavelength of the light incident on the optical fiber. Therefore, pressure changes are detected and measured by monitoring changes in the optical spectrum of the light reflected by the total reflection mirror with a spectroscope.

[0004] However, the system, which includes a spectrometer that monitors the wavelength change of the reflected light, is complex and precise, which increases the cost of the entire device.In addition, since pressure is measured by monitoring minute positional movements as wavelength changes, it is difficult to improve the measurement sensitivity.

[0005] Japanese Patent Application Laid-Open No. 2019-187646

[0006] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical fiber pressure sensor and an optical fiber pressure measuring instrument that can achieve either or both of low cost and high sensitivity.

[0007] The above object is achieved by the present invention as follows. That is, one aspect of the present invention is as follows: <1> An optical fiber pressure sensor that detects pressure at one end of an optical fiber, comprising: the optical fiber; a tubular portion into which the one end of the optical fiber is inserted through one opening and fixed; a pressure-sensitive portion that is axially movable within the tubular portion and includes a reflecting surface disposed opposite an end of the one end of the optical fiber and a pressure-receiving surface facing away from the reflecting surface and facing the other opening of the tubular portion; and an elastic body interposed between the tubular portion and the pressure-sensitive portion, which applies a repulsive force to movement of the pressure-sensitive portion in a direction toward the one end of the optical fiber. <2> The optical fiber pressure sensor according to <1>, further comprising a restricting means for restricting movement of the pressure-sensitive portion in a direction away from the one end of the optical fiber when no pressure is applied to the pressure-receiving surface. <3> The optical fiber pressure sensor according to <2>, wherein the restricting means is a protruding piece extending from an edge of the other opening of the tubular portion toward the center of the opening. <4> The optical fiber pressure sensor according to <2>, wherein the regulating means is a mesh provided at the other opening of the tubular portion. <5> The optical fiber pressure sensor according to <1>, wherein the pressure-sensing portion is rod-shaped, and wherein the reflective surface is provided at one end of the pressure-sensing portion and the pressure-receiving surface is provided at the other end. <6> The optical fiber pressure sensor according to <1>, wherein the elastic body is an elastic tube or a spring. <7> The optical fiber pressure sensor according to <1>, wherein the elastic body is a silicone rubber tube. <8> An optical fiber pressure measuring instrument comprising the optical fiber pressure sensor according to <1>, a light source that inputs light to an end portion on the other end side of the optical fiber, and a photodetector that irradiates the reflective surface with light that is input to the other end side of the optical fiber and emitted from the one end side of the optical fiber, and measures the intensity of the reflected light.

[0008] According to the present invention, it is possible to provide an optical fiber pressure sensor and an optical fiber pressure measuring instrument that can achieve either low cost or high sensitivity, or both.

[0009] FIG. 1 is a cross-sectional view showing an optical fiber pressure sensor according to an embodiment that is an exemplary aspect of the present invention. FIG. 2 is an enlarged cross-sectional view of a main part of a sensor main body in an optical fiber pressure sensor according to an embodiment that is an exemplary aspect of the present invention. FIG. 3 is a schematic configuration diagram showing a state in which a pressure test is being performed on an optical fiber pressure measuring instrument according to an embodiment. FIG. 4 is an enlarged cross-sectional view of a main part of a sensor main body in an optical fiber pressure sensor according to a first modified example that is an exemplary aspect of the present invention. FIG. 5 is an enlarged cross-sectional view of a main part of a sensor main body in an optical fiber pressure sensor according to a second modified example that is an exemplary aspect of the present invention. FIG. 6 is an enlarged cross-sectional view of a main part of a sensor main body in an optical fiber pressure sensor according to a third modified example that is an exemplary aspect of the present invention. FIG. 7 is an enlarged cross-sectional view of a main part of a sensor main body in an optical fiber pressure sensor according to a fourth modified example that is an exemplary aspect of the present invention. FIG. 8 is a graph showing the results of a test to confirm the effect of an optical path difference on reflected light intensity, which is one of the verification tests. FIG. 9 is a graph showing the results of a pressure measurement verification test, which is one of the verification tests.

[0010] Hereinafter, an optical fiber pressure sensor and an optical fiber pressure measuring instrument according to embodiments of the present invention will be specifically described with reference to the drawings.

[0011] 1 is a cross-sectional view showing an optical fiber pressure sensor according to an embodiment. As shown in Fig. 1, the optical fiber pressure sensor 1 according to the embodiment (hereinafter sometimes simply referred to as "pressure sensor 1") includes an optical fiber 10 and a sensor main body 100 attached to one end of the optical fiber 10.

[0012] Fig. 2 is an enlarged cross-sectional view of a main portion of the sensor main body 100 of the pressure sensor 1. As shown in Figs. 1 and 2, the sensor main body 100 has a tubular portion 20, a pressure-sensitive portion 30, and a spring 40, which is an elastic body. In Figs. 1 and 2, the tip end side of the pressure sensor 1 and the optical fiber 10 is indicated by an arrow t, and the base end side is indicated by an arrow b (the same applies to the subsequent figures). In Figs. 1 and 2, the central axis of the tubular portion 20 and the pressure-sensitive portion 30 is indicated by a dashed dotted line P (hereinafter referred to as the "central axis P" or "axis P"). The pressure sensor 1 is a device that detects pressure using the sensor main body 100 on one end side (tip end side t) of the optical fiber 10.

[0013] The optical fiber 10 is generally made of a resin (plastic) or quartz member. The optical fiber 10 in this embodiment is a single-core optical fiber consisting of a core located radially toward the center and a cladding located on the outer periphery of the core. The relative refractive index difference between the core and the cladding of the optical fiber 10 is, for example, 0.1% or more and 11% or less.

[0014] In this embodiment, the tubular portion 20 is composed of a cylindrical small diameter portion 21 and a large diameter portion 22, and the small diameter portion 21 is fitted into and fixed to the large diameter portion 22. One end side (tip side) of the optical fiber 10 is inserted into and fixed to the tubular portion 20 from one opening (opening on the small diameter portion 21 side) 23 of the tubular portion 20. Therefore, the inner diameter of the small diameter portion 21 is approximately the same as the outer diameter of the optical fiber 10.

[0015] If the optical fiber 10 is thinner and it is difficult to make the inner diameter of the small diameter portion 21 approximately the same as the outer diameter of the optical fiber 10, an auxiliary tubular portion may be interposed, having an inner diameter approximately the same as the outer diameter of the optical fiber 10 and an outer diameter approximately the same as the inner diameter of the small diameter portion 21. That is, by fitting the auxiliary tubular portion into the small diameter portion 21 and fitting the optical fiber 10 into the auxiliary tubular portion and fixing them appropriately, one end side (tip side t) of the optical fiber 10 is inserted into one opening (opening on the small diameter portion 21 side) 23 in the tubular portion 20 and fixed therein.

[0016] The cylindrical portion 20 may be made of any material, such as metals such as stainless steel or aluminum, various resins, glass, etc. The material may be changed depending on the portion, such as making the small diameter portion 21 out of stainless steel and the large diameter portion 22 out of resin.

[0017] In this embodiment, the pressure-sensing unit 30 is rod-shaped and has a cylindrical small-diameter portion 31 and a cylindrical large-diameter portion 32 coaxially arranged therewith. A step surface 35 is formed at the boundary between the small-diameter portion 31 and the large-diameter portion 32, protruding by the difference in diameter between the two portions and facing the base end. The pressure-sensing unit 30 is an integrally molded component made of metal such as stainless steel. In the pressure-sensing unit 30, the large-diameter portion 32 is located within the large-diameter portion 22 of the tubular portion 20, and a portion of the small-diameter portion 31 is inserted into the small-diameter portion 21 of the tubular portion 20.

[0018] The pressure-sensing portion 30 is movable in the axial direction (direction on the central axis P) within the cylindrical portion 20. The outer diameter of the large-diameter portion 32 in the pressure-sensing portion 30 is approximately the same as the inner diameter of the large-diameter portion 22 in the cylindrical portion 20, and the outer diameter of the small-diameter portion 31 in the pressure-sensing portion 30 is approximately the same as the inner diameter of the small-diameter portion 21 in the cylindrical portion 20. However, slight gaps are provided between the large-diameter portion 32 in the pressure-sensing portion 30 and the large-diameter portion 22 in the cylindrical portion 20, and between the small-diameter portion 31 in the pressure-sensing portion 30 and the small-diameter portion 21 in the cylindrical portion 20, to an extent that the pressure-sensing portion 30 can move freely in the axial direction (direction on the central axis P) within the cylindrical portion 20.

[0019] The pressure-sensing unit 30 has a reflecting surface 33 at one end (the end on the base end side b, the end on the side of the small diameter portion 31) and a pressure-receiving surface 34 at the other end (the end on the tip side t, the end on the side of the large diameter portion 32). The reflecting surface 33 of the pressure-sensing unit 30 is disposed opposite the end 11 on one end side (the tip side t) of the optical fiber 10. The pressure-receiving surface 34 of the pressure-sensing unit 30 is back-to-back with the reflecting surface 33 and faces the other opening 24 of the tubular portion 20 (the opening on the side of the large diameter portion 22). Pressure is applied to the pressure-receiving surface 34 of the pressure-sensing unit 30 by the influence of external air pressure or water pressure (or the liquid pressure of the liquid in the case of a liquid other than water) via a through-hole 52, which will be described later.

[0020] The spring (elastic body) 40 is interposed between the cylindrical portion 20 and the pressure-sensing portion 30. More specifically, when the small diameter portion 31 of the pressure-sensing portion 30 is inserted, the spring 40 is interposed between the end face 21t on the tip side t of the small diameter portion 21 located within the large diameter portion 22 and the stepped surface 35 of the pressure-sensing portion 30.

[0021] The spring 40 is configured so that a repulsive force of the spring 40 acts against movement of the pressure-sensing unit 30 in a direction (indicated by arrow b) approaching the end 11 on one end side (tip side t) of the optical fiber 10. In other words, the spring 40 is in a natural state where it is not stretched or contracted, or in a contracted state, when no pressure is applied to the pressure-receiving surface 34 (no load is applied in the direction of arrow b), and when the pressure-sensing unit 30 moves in a direction (indicated by arrow b) approaching the end 11 and the spring 40 contracts or contracts further, a repulsive force is applied.

[0022] A cap 50 is fixed to the tip end t of the tubular portion 20. The material of the cap 50 may be metal, resin, or the like, and is not particularly limited. The cap 50 is cylindrical with an inner diameter approximately the same as that of the large-diameter portion 22 of the tubular portion 20. The tip end t of the cap 50 is provided with a protruding piece 51 that extends annularly toward the center (toward the central axis P). Therefore, in the tubular portion 20, the annular protruding piece 51 extends from the edge 24e of the other opening 24 toward the central axis P. Therefore, the opening 24 in the tubular portion 20 is a through-hole 52 whose opening diameter is narrowed by the amount of the annular protruding piece 51. In other words, the tip end t of the sensor main body 100 has a so-called aperture shape.

[0023] This protruding piece 51 functions as a restricting means for restricting movement of the pressure-sensing unit 30 in a direction (direction of arrow t) away from the end 11 on one end side (tip side t) of the optical fiber 10 when no pressure is applied to the pressure-receiving surface 34. Therefore, when no pressure is applied to the pressure-receiving surface 34, the protruding piece 51 in contact with the pressure-receiving surface 34 restricts movement of the pressure-sensing unit 30 in the direction of arrow t, so that the pressure-sensing unit 30 will not fall off from the sensor main body 100.

[0024] Furthermore, without a regulating means, when measuring pressure as a pressure sensor, the pressure value tends to fluctuate over time even though the actual pressure is constant, which is known as drift. However, by providing the protruding piece 51 as a regulating means, the occurrence of this drift can be suppressed.

[0025] When no pressure is applied to the pressure-receiving surface 34, a constant distance (gap) is maintained between the reflecting surface 33 of the pressure-sensing unit 30 and the end 11 on one end side (tip side t) of the optical fiber 10. When the sensor main body 100 is placed in a pressurized environment, pressure is applied to the pressure-receiving surface 34 exposed to the outside through the through-hole 52, causing the pressure-sensing unit 30 to move in the direction of arrow b, and the reflecting surface 33 of the pressure-sensing unit 30 to approach the end 11 on one end side (tip side t) of the optical fiber. The repulsive force of the spring 40 causes the distance (gap) between the reflecting surface 33 and the end 11 to decrease in inverse proportion to the magnitude of the pressure applied to the pressure-receiving surface 34.

[0026] The pressure sensor 1 according to the present embodiment as described above can be used as an optical fiber pressure measuring instrument by being used together with a light source and a photodetector. Fig. 3 is a schematic diagram showing the configuration of an optical fiber pressure measuring instrument 60 according to the present embodiment, in which a pressure test is being performed.

[0027] The optical fiber pressure measuring instrument 60 measures by inserting one end of an optical fiber 10, which has a sensor body 100 attached to its end, into a fine tube (such as a blood vessel) to be measured. FIG. 3 shows the state in which one end of the optical fiber 10 is inserted into a pressure chamber 71, the internal pressure of which is controlled by pressurizing it with a pressurizer 72.

[0028] As shown in FIG. 3 , an optical fiber pressure measuring instrument 60 according to an embodiment (hereinafter, sometimes simply referred to as the “pressure measuring instrument 60”) includes the optical fiber pressure sensor 1 according to this embodiment, a light source 62 that inputs light to the end 12 on the other end side (base end side b) of the optical fiber 10, an optical distributor 61 that distributes the light midway through the optical fiber 10, and a photodetector 63 that receives the light distributed by the optical distributor 61 via an optical fiber 64 and measures the intensity.

[0029] The light source 62 generates visible light or laser light. When generating laser light, the light source 62 has a semiconductor laser, and generates laser light by passing electricity through the semiconductor laser to cause laser oscillation. The light source generates red to near-infrared laser light having a wavelength of 670 nm or more and 1600 nm or less, for example.

[0030] The optical distributor 61 is a device that has a function of distributing the reflected light from the optical fiber 10 to the optical fiber 64 when the light emitted from the end 11 on one end side (tip side t) of the optical fiber 10 is reflected by the reflecting surface 33 and the reflected light enters the optical fiber 10 again. An optical fiber coupler, an optical circulator, or the like can be used as the optical distributor 61.

[0031] In the pressure measuring instrument 60, when light is emitted from the light source 62, it enters the end 12 at the other end (base end side b) of the optical fiber 10, passes through the optical fiber 10, and exits from the end 11 at one end side (tip side t) of the optical fiber. The reflective surface 33 of the pressure sensitive unit 30 faces the end 11, and the light exiting from the end 11 is reflected by the reflective surface 33 and returns to the end 11. The reflected light that has returned to the end 11 enters the optical fiber 10 again and travels toward the base end side b. The reflected light then passes through the optical fiber 64 by the optical distributor 61 to the photodetector 63, where the intensity of the reflected light is measured.

[0032] When pressure is applied to the pressure-receiving surface 34 and the gap between the reflecting surface 33 and the end 11 becomes smaller, the light emitted from the light source 62 is reflected by the reflecting surface 33 as reflected light, and the total length of the light that finally reaches the photodetector 63 becomes shorter. By measuring the change in the light signal information due to this shortening of the total length (i.e., the optical path difference) with the photodetector 63, the magnitude of the pressure received by the pressure-receiving surface 34 can be determined.

[0033] In the technology described in Patent Document 1, the reflecting surface (total reflection mirror 512) fixed to the diaphragm moves due to the action of pressure only within the scope of minute movements of the diaphragm, and the optical path difference is only a very small difference on the order of wavelength less than 1 μm. Therefore, in order to read this optical path difference, it was necessary to detect and measure pressure changes by monitoring changes in the optical spectrum of the light reflected from the reflecting surface with a spectroscope.

[0034] In this embodiment, the pressure-sensing unit 30 equipped with the reflective surface 33 can move relatively far in the direction of the central axis P while being restricted by the repulsive force of the spring 40 and the protruding piece 51. The stroke over which the pressure-sensing unit 30 can move ranges from several tens to several hundreds of micrometers, depending on the design, and therefore the optical path difference appears as a difference in the intensity of light. Therefore, in this embodiment, the optical path difference can be read by measuring the intensity of the reflected light using the photodetector 63.

[0035] According to this embodiment, because the stroke of movement of the pressure-sensitive unit 30 in response to a pressure change is large, pressure can be measured by measuring the intensity of reflected light with the photodetector 63. This allows for a simpler device compared to a complex and precise system including a spectrometer that monitors wavelength changes in reflected light, thereby achieving lower costs. Furthermore, because the stroke of movement of the pressure-sensitive unit 30 in response to a pressure change is large, the pressure-sensitive unit 30 moves linearly in response to pressure changes, which can be expected to result in precise measurements and high sensitivity. Of course, it is also possible to achieve even lower costs by sacrificing high sensitivity in favor of a simpler configuration, or to achieve even higher sensitivity by sacrificing low cost in favor of a more sophisticated structure.

[0036] [Modifications] Four modifications of the embodiment described above, each having a different structure of the sensor main body 100, will be described with reference to the drawings. Note that in each of the following modifications, only some of the configurations are different from those of the above embodiment, and the rest are the same as those of the above embodiment. Therefore, in each modification, the description will focus on the characteristic configuration of each modification, and components having the same configuration and function as those of the above embodiment will be assigned the same reference numerals as those in Figures 1 and 2, which show the above embodiment, and detailed description thereof will be omitted.

[0037] (First Modification) Fig. 4 is an enlarged cross-sectional view of a main part of a sensor main body in an optical fiber pressure sensor according to a first modification. The sensor main body 200 according to this modification differs in that an elastic tube is used as the elastic body instead of a spring 40. That is, as shown in Fig. 4, a tube (elastic body) 41 is interposed between the cylindrical portion 20 and the pressure-sensing portion 30.

[0038] The tube 41 is configured so that a repulsive force of the tube 41 acts against movement of the pressure-sensing unit 30 in a direction (in the direction of arrow b) approaching the end 11 on one end side (tip side t) of the optical fiber 10. In other words, the tube 41 is in a natural state where it is not stretched or contracted, or in a contracted state, when no pressure is applied to the pressure-receiving surface 34 (no load is acting in the direction of arrow b), and when the pressure-sensing unit 30 moves in the direction (in the direction of arrow b) approaching the end 11 and the tube 41 contracts or contracts further, a repulsive force is applied.

[0039] The material of the tube 41 is not particularly limited as long as it has rubber elasticity, but it is particularly preferable that the tube be made of silicone rubber, which has excellent stability and durability in various usage environments.

[0040] In both this modified example and the above embodiment, the elastic body (tube 41, spring 40) is provided with a restoring force that acts as a repulsive force to restore the contracted state of the elastic body, but the elastic body may be incorporated so that a restoring force that acts as a repulsive force to restore the expanded state of the elastic body. The state in which the elastic body is incorporated in this way is also included in the state in which the elastic body is interposed between the cylindrical portion 20 and the pressure-sensing portion 30.

[0041] (Second Modification) Figure 5 is an enlarged cross-sectional view of a main portion of a sensor main body in an optical fiber pressure sensor according to a second modification. In a sensor main body 300 according to this modification, the shape of a cap 50a is different from that of the cap 50 of the embodiment. That is, as shown in Figure 5, a protruding piece 51a provided at the end of the tip side t of the cap 50a is not annular like the protruding piece 51, but has a claw-like shape with a portion of the circumferential direction extending toward the center (toward the central axis P). Therefore, only the claw-like protruding piece 51a covers the opening 24 in the tubular portion 20, and most of the area of ​​the opening 24 is a through hole 52a.

[0042] This protruding piece 51a functions as a restricting means for restricting movement of the pressure-sensing unit 30 in a direction (direction of arrow t) away from the end 11 on one end side (tip side t) of the optical fiber 10 when no pressure is applied to the pressure-receiving surface 34. Therefore, when no pressure is applied to the pressure-receiving surface 34, the protruding piece 51a in contact with the pressure-receiving surface 34 restricts movement of the pressure-sensing unit 30 in the direction of arrow t, so that the pressure-sensing unit 30 does not fall off from the sensor main body 300. Furthermore, by providing the protruding piece 51a as a restricting means, it is possible to suppress the occurrence of so-called drift, as in the embodiment and the first modified example.

[0043] (Third Modification) Figure 6 is an enlarged cross-sectional view of a main portion of a sensor main body in an optical fiber pressure sensor according to a third modification. In a sensor main body 400 according to this modification, the shape of a cap 50b is different from that of the cap 50 of the embodiment and the cap 50a of the second modification. That is, as shown in Figure 6, the end of the tip side t of the cap 50b is provided with a mesh 51b that covers the entire opening 24 in the tubular portion 20, rather than a protruding piece like the protruding piece 51 or the protruding piece 51a. Therefore, the mesh 51b that exists throughout the entire opening 24 in the tubular portion 20 forms through-holes 52b.

[0044] This mesh 51b functions as a restricting means for restricting movement of the pressure-sensing unit 30 in a direction (direction of arrow t) away from the end 11 on one end side (tip side t) of the optical fiber 10 when no pressure is applied to the pressure-receiving surface 34. Therefore, when no pressure is applied to the pressure-receiving surface 34, the mesh 51b abutting against the pressure-receiving surface 34 restricts movement of the pressure-sensing unit 30 in the direction of arrow t, so that the pressure-sensing unit 30 does not fall off from the sensor main body 400. Furthermore, by providing the mesh 51b as a restricting means, it is possible to suppress the occurrence of so-called drift, as in the embodiment and other modified examples.

[0045] 7 is an enlarged cross-sectional view of a main part of a sensor body in an optical fiber pressure sensor according to a fourth modification. In the sensor body 500 according to this modification, the shape of the cap 50c is different from the cap 50 of the embodiment and the caps 50a and 50b of the second and third modifications.

[0046] In this embodiment, a protruding piece 51c having a shape similar to that of the protruding piece 51a of the second modified example is provided on the cap 50c. However, in this embodiment, the protruding piece 51c is provided on the inner circumferential surface of the peripheral wall 54 of the cap 50c, rather than on the end of the tip side t of the cap 50c. The peripheral wall 54 of the cap 50c extends further in the direction of arrow t from the position where the protruding piece 51c is provided, and the end of the tip side t of the cap 50c is closed by the top plate 53. Therefore, in this modified example, there is no through hole on the side of the other opening 24 in the tubular portion 20 in the direction of arrow t.

[0047] In this embodiment, the pressure-receiving surface 34 and the top plate 53 are spaced apart, and the area surrounded by the pressure-receiving surface 34, the top plate 53, and the peripheral wall 54 forms a semi-closed space 55. A portion of the peripheral wall 54 in the semi-closed space 55 is open to form a through-hole 52c. The semi-closed space 55 is configured to have the same pressure as the outside via the through-hole 52c. Therefore, in this modified example, as in the embodiment and other modified examples, the pressure applied to the pressure-receiving surface 34 is the same as the pressure in the environment in which the sensor main body 400 is located.

[0048] The protruding piece 51c functions as a restricting means for restricting movement of the pressure-sensing unit 30 in a direction (direction of arrow t) away from the end 11 on one end side (tip side t) of the optical fiber 10 when no pressure is applied to the pressure-receiving surface 34. Therefore, when no pressure is applied to the pressure-receiving surface 34, the protruding piece 51c in contact with the pressure-receiving surface 34 restricts movement of the pressure-sensing unit 30 in the direction of arrow t, so that the pressure-sensing unit 30 does not fall off from the sensor main body 500. Furthermore, by providing the protruding piece 51c as a restricting means, it is possible to suppress the occurrence of so-called drift, as in the embodiment and other modified examples.

[0049] As described above, the pressure-receiving surface 34 of the pressure-sensing unit 30 does not need to have a through-hole at the opposing position, as long as it is configured to receive pressure from the external environment.

[0050] [Verification Test] The optical fiber pressure sensor 1 according to the embodiment shown in FIGS. 1 and 2 was manufactured for verification purposes according to the following specifications, and a verification test was carried out by assembling the optical fiber pressure measuring instrument 60 shown in FIG.

[0051] (Specifications) Type of optical fiber 10: single-mode quartz fiber Core diameter of optical fiber 10: 50 μm or 120 μm Outer diameter and numerical aperture of optical fiber 10: 100 to 1000 μm (typical condition: 140 μm), NA=0.22 Material, outer diameter, and length of small diameter portion 21 of tubular portion 20: stainless steel, 0.5 to 1.5 mm (typical condition: 0.9 mm), 1 to 16 mm (typical condition: 8 mm) Material, outer diameter, and length of large diameter portion 22 of tubular portion 20: polyimide, 0.7 to 1.7 mm (typical condition: 0.9 mm), 1 to 16 mm (typical condition: 5 mm) - An auxiliary tubular portion (outer diameter 0.3 to 1.3 mm (typical condition 0.6 mm)) is present between the small diameter portion 21 and the optical fiber 10 - Diameter of the reflecting surface 33 (thin diameter portion 31) in the pressure sensing portion 30: 0.3 to 1.3 mm (typical condition 0.4 mm) - Diameter of the pressure receiving surface 34 in the pressure sensing portion 30: 0.6 mm - Length of the thin diameter portion 31 in the pressure sensing portion 30 in the axial direction P: 2.0 to 6.0 mm (typical condition 2 mm) - Length of the thick diameter portion 32 in the pressure sensing portion 30 in the axial direction P: 1.0 to 3.0 mm (typical condition 1 mm) - Material of the pressure sensing portion 30: Stainless steel (reflecting surface 33 is polished) - Gap between the reflecting surface 33 and the end portion 11 when no pressure is applied to the pressure receiving surface 34: 0.2 mm Material and molding of the cap 50: A heat-shrinkable tube made of elastomer (polyether block amide copolymer) is used, and the tip is heated and shrunk to form a simple aperture structure (protruding piece 51) (diameter of the through hole 52: 0.3 to 1.3 mm (representative condition: 0.6 mm)).

[0052] (Test to confirm the effect of optical path difference on reflected light intensity) The spring 40 was removed from the optical fiber pressure sensor 1 under representative conditions, and the gap G between the reflective surface 33 of the pressure-sensing unit 30 and the end 11 of one end (tip side t) of the optical fiber 10 was varied from 0 μm to 100 μm. The reflectance (intensity of reflected light / intensity of emitted light) of the light emitted from the light source 62 and reflected by the reflective surface 33 was measured using the photodetector 63. The test was conducted using two optical fibers 10 with core diameters r of 50 μm and 120 μm. The results are shown in the graph in FIG. 8. The graph in FIG. 8 is plotted with the gap G (μm) on the horizontal axis and the reflectance (%) on the vertical axis.

[0053] For optical fibers 10 with any core diameter r, the reflectivity is 70% in the optical path consisting of only the optical fiber 10 and the optical distributor 61 (when the reflective surface 33 and the end 11 are in contact and the gap G is 0 μm), and it can be seen that the reflectivity decreases as the gap G (μm) increases. The reflectivity decreases significantly even when the gap G is several tens of μm, which indicates that when pressure is applied to the pressure-receiving surface 34, the pressure-sensing unit 30 moves and the gap G becomes smaller, resulting in a significant decrease in reflectivity. For an optical fiber 10 with a core diameter r = 50 μm, the reflectivity increases by more than three times when the pressure-sensing unit 30 is moved from a gap G = 100 μm to a gap G = 0 μm.

[0054] From the above results, it can be seen that if the movable stroke of the pressure-sensing unit 30 can be secured to be several tens of microns to a hundred microns or more, it is possible to sufficiently measure pressure simply by measuring the intensity of reflected light. Taking into account the above results and other characteristics of the verification optical fiber pressure sensor 1, a change in pressure of 1 mmHg (≒ 133 Pa) will cause the intensity of reflected light to fluctuate by 1.01 times, or 1%. This is sufficiently higher than other electrical and optical noise, so it can be seen that a pressure difference of 1 mmHg can be detected without any problems.

[0055] (Pressure Measurement Verification Test) Using the optical fiber pressure sensor 1 under representative conditions, the pressure in the pressurizing chamber 71 was increased or decreased arbitrarily for 90 minutes by manually operating the pressurizer 72, and the intensity of reflected light was measured with the photodetector 63, and the change over time was recorded. A separate precision pressure sensor was installed in the pressurizing chamber 71 as a reference sensor, and the change over time was also recorded. The results are shown in the graph in FIG. 9.

[0056] The graph in Fig. 9 is plotted with time (seconds) on the horizontal axis and pressure values ​​(left scale, mmHg) from the reference sensor and intensity of light reflected by the photodetector 63 of the pressure sensor 1 of the embodiment (right scale, standard value) on the vertical axis. However, the graph in Fig. 9 only shows the results between 1550 seconds (25 minutes 50 seconds) and 1800 seconds (30 minutes) out of the total test time of 90 minutes.

[0057] It was confirmed that during the 90-minute test period, the intensity of the reflected light by the photodetector 63 increased and decreased linearly in response to the increase and decrease in pressure inside the pressure chamber 71. Looking at the graph in Figure 9, it can be seen that the fluctuations in pressure detected by the reference sensor and the fluctuations in the intensity of the reflected light by the photodetector 63 are synchronized.

[0058] The above-described embodiment and four modified examples merely show examples of typical forms of the present invention, and the present invention is not limited to the above-described embodiment and modified examples. For example, in the above-described embodiment and modified examples, the cylindrical portion and the cap are configured as separate members, but the present invention is not limited to this, and the protruding piece, mesh, etc. may be molded integrally with the cylindrical portion.

[0059] Furthermore, in the above-described embodiments and modified examples, an example is given in which the cylindrical portion is formed of two members, a small diameter portion and a large diameter portion, but the present invention is not limited to this, and the cylindrical portion may be formed by integral molding so that the small diameter portion and the large diameter portion are formed, or the cylindrical portion may have a shape with a constant outer diameter.

[0060] In addition, those skilled in the art can implement various modifications in accordance with conventionally known knowledge without departing from the gist of the present invention. As long as such modifications still comprise the configuration of the optical fiber pressure sensor and optical fiber pressure measuring instrument of the present invention, they are of course included in the scope of the present invention.

[0061] Optical fiber pressure sensors and optical fiber pressure measuring instruments can be used in various fields to measure pressure inside fine tubes, etc. For example, in medical settings, they can be used inside blood vessels to measure blood pressure. They can also be used in a wide range of other fields, such as infrastructure facilities (for example, measuring pressure inside sewer pipes) and geological engineering.

[0062] 1: Pressure sensor (optical fiber pressure sensor), 10, 64: Optical fiber, 11: End (end on one end side), 12: End (end on the other end side), 20: Cylindrical portion, 21: Small diameter portion, 22: Large diameter portion, 23: One opening, 24: Other opening, 30: Pressure-sensing portion, 31: Thin diameter portion, 32: Large diameter portion, 33: Reflecting surface, 34: Pressure-receiving surface, 35: Step surface, 40: Spring (elastic body), 41: Tube (elastic body), 50, 50a, 50b, 50c: Cap, 51, 51a, 51c: Projecting piece, 51b: Mesh, 52, 52a, 52b, 52c: Through-hole, 53: Top plate, 54: Peripheral wall, 55: Semi-closed space, 60: Optical fiber pressure measuring device, 61: Light distributor, 62: Light source, 63: Photodetector, 71: Pressurizing chamber, 72: Pressurizer, 100, 200, 300, 400, 500: Sensor main body

Claims

1. An optical fiber pressure sensor that detects pressure at one end of an optical fiber, comprising: the optical fiber; a tubular portion into which one end of the optical fiber is inserted from one opening and fixed; a pressure-sensitive portion that has a reflective surface that is arranged opposite to the end of one end of the optical fiber and a pressure-receiving surface that faces away from the reflective surface and faces the other opening of the tubular portion, and is movable axially within the tubular portion; and an elastic body that is interposed between the tubular portion and the pressure-sensitive portion and that applies a repulsive force to the pressure-sensitive portion when it moves in a direction approaching the end of one end of the optical fiber.

2. An optical fiber pressure sensor as described in claim 1, further comprising a restricting means for restricting movement of the pressure-sensitive portion away from the end of one end of the optical fiber when no pressure is applied to the pressure-receiving surface.

3. The optical fiber pressure sensor according to claim 2, wherein the restricting means is a protruding piece extending from the edge of the other opening in the cylindrical portion toward the center of the opening.

4. The optical fiber pressure sensor according to claim 2, wherein the restricting means is a mesh provided at the other opening of the cylindrical portion.

5. The optical fiber pressure sensor according to claim 1, wherein the pressure-sensitive portion is rod-shaped, and the pressure-sensitive portion has the reflecting surface at one end and the pressure-receiving surface at the other end.

6. The optical fiber pressure sensor according to claim 1, wherein the elastic body is an elastic tube or a spring.

7. The optical fiber pressure sensor according to claim 1, wherein the elastic body is a tube made of silicone rubber.

8. An optical fiber pressure measuring device comprising: an optical fiber pressure sensor according to claim 1; a light source that inputs light to the other end of said optical fiber; and a photodetector that measures the intensity of the reflected light when the light that is input to the other end of said optical fiber and emitted from one end of said optical fiber is irradiated onto said reflecting surface.

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