JPH08219983A - Optical fiber and fiber-optic sensor - Google Patents

Abstract

PURPOSE: To prevent foreign substances from adhering to an optical fiber during the storage and easily manage the optical fiber while maintaining the mechanical strength, by forming a void in a core part of the optical fiber having a clad in the outer periphery of a core. CONSTITUTION: A void 12 is opened by a grinder at the center of a cylindrical base material for an optical fiber which has a core 13 consisting of a quartz clad 14 and glass having its refractive index increased by the addition of Ge in quartz. The base material is drawn thereby to form an optical fiber 11 with the glad 14 having a minute outer diameter of approximately 250μm. A coating material 16 is formed of resin set by ultraviolet rays in the periphery of the optical fiber 11, whereby an optical fiber 11b is completed. The diameter of the void 12 is approximately 100μm and the outer diameter of the core 13 is approximately 110μm. The optical fiber 11b is cut to fiber-optic sensors each having a length of about 5-20cm. Before storing the fiber-optic sensors, both ends of every fiber-optic sensor are sealed by a sealing foil to prevent the invasion of dust, moisture, etc., into the void 12 during the storage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber and an optical fiber sensor using the optical fiber as a sensing medium.

[0002]

2. Description of the Related Art A substance sensor that uses an optical fiber to analyze components such as gas and liquid and to detect the presence or absence or concentration of the substance generally detects changes in the intensity and phase of light propagating through the optical fiber. Therefore, in order to change the intensity and phase of the light propagating in the optical fiber depending on the presence or absence of the substance to be sensed and its state, at least a part of the electromagnetic field distribution of the propagating light needs to interact with the substance. is there. As a general method therefor, at least a part of the propagating light is once output to the outside of the optical fiber, interacts with the substance to be detected, and then returned to the inside of the optical fiber, and an evanescent light of the propagating light ( evanescent: It is known to use light. Here, the light leaching to the outside of the core of the optical fiber is called evanescent light, and its intensity is rapidly attenuated as the distance from the axis of the optical fiber increases.

In the former method, for example, as shown in FIG. 18, a light beam 3 is transmitted from an optical fiber 1a through a lens 2a.
Since it has a portion for emitting light and a portion for recombining the light beam 3 with the optical fiber 1b via the lens 2b, the structure becomes complicated as compared with the latter method. 4 is a cell and 5 is a substance to be detected. In the latter method, a part of the clad layer of the optical fiber is intentionally made thin, and leaching of light occurs at the outside of the optical fiber at this part, and the substance to be detected is brought close to this part. Perform sensing. For example, as shown in FIG. 19, there is a method in which a part of the cladding layer 6 of the optical fiber 1 is removed by a method such as polishing to locally form a light seeping portion 6a. Further, as shown in FIG. 20, there is also a method of obtaining continuous leaching in the longitudinal direction by using the optical fiber 1 having a structure in which the core 7 is decentered from the center instead of the center of the optical fiber 1.

[0004]

The above-mentioned method utilizing the seepage of light has the following problems due to the presence of the coating material that covers the outside of the optical fiber. That is, 1) The sensing ability of a substance is reduced depending on the properties of the coating material. Therefore, it becomes necessary to carefully select the refractive index and light transmittance of the coating material. 2) When an appropriate coating material cannot be obtained, the coating material may not be applied or only the sensing portion may be removed. However, if the coating material is removed, the reliability of the strength of the optical fiber is significantly deteriorated, which causes a serious problem in practical use in the laying method and life. 3) If scratches or other substances adhere to the surface where light seeps out, it will affect the sensing.
It is important to control the surface condition when transporting and storing the sensor.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides an optical fiber and an optical fiber sensor which solve the above-mentioned problems, and a core made of a material having a light transmitting property and a relatively high refractive index, An optical fiber having a clad made of a material having a relatively low refractive index provided on the outer periphery of a core, wherein an optical fiber is characterized in that a hole is provided inside the core cross section, which is a first invention. . The optical fiber 11 of the present invention has a structure as shown in FIG. 1, for example.
In the figure, 12 is a hole, 13 is a core, and 14 is a clad.

Further, an optical fiber according to the first invention is characterized in that an inner layer made of a material having a relatively lower refractive index than that of the core is provided on the inner surface of the hole provided in the core. The optical fiber 11a of the present invention has a structure as shown in FIG. 2, for example. In the figure, 15 is an inner layer.

Further, an optical fiber according to the first and second inventions is characterized in that the outer periphery of the clad is covered with a coating material, which is a third invention. Optical fiber 11 of the present invention
b has a structure as shown in FIG. 3, for example. In the figure,
Reference numeral 16 is a coating material.

Further, in the optical fiber sensor utilizing the evanescent light of the light propagating through the optical fiber, the substance to be detected is introduced into the hole of the optical fiber of the first, second or third invention and propagates through the core. A fourth invention is an optical fiber sensor characterized in that a substance to be detected is detected by a change in light intensity, phase or their spectral characteristics.

Further, a fifth invention is an optical fiber sensor according to the fourth invention, characterized in that a means for reflecting light propagating through the core is provided on one end side of the optical fiber. The optical fiber 11 used in the present invention is provided with a light reflecting material 17 at one end as shown in FIG. 4, for example.

Further, in an optical fiber having a core made of a material having a light transmittance and a relatively high refractive index, and a clad made of a material having a relatively low refractive index provided on the outer periphery of the core, A sixth invention is an optical fiber, which is characterized in that holes are provided mainly inside the cladding cross section. The optical fiber 71 of the present invention is shown in FIG.
The structure is as shown in (a) and (b). 7 in the figure
2 is a hole, 73 is a core, 74 is a clad, and 75 is a covering material. A dressing 75 may be coated as shown. 9A shows the case where there are two holes 72, and FIG. 9B shows the case where there is one hole 72.

Further, an optical fiber according to the sixth aspect of the invention is characterized in that three or more holes are provided mainly inside the cladding cross section as a seventh aspect of the invention. The optical fiber 71 of the present invention has a structure as shown in FIGS. 10 (a) and 10 (b), for example. In addition, FIG.
2 shows the case where there are four holes, and FIG. 10B shows the case where there are three holes 72.

Further, in the seventh aspect of the invention, the plurality of holes mainly provided inside the cladding cross section have substantially the same shape and size, and are substantially equal to each other at substantially the same distance from the core. An eighth aspect of the present invention is an optical fiber characterized by being arranged at equal intervals. The optical fiber 71 of the present invention is, for example, as shown in FIG.
The holes 72 are arranged at a distance A from the core at equal intervals B.

Further, in the optical fiber sensor utilizing the evanescent light of the light propagating through the optical fiber, the substance to be detected is introduced into the hole of the optical fiber of the sixth, seventh or eighth invention and propagated through the core. A ninth invention is an optical fiber sensor characterized in that a substance to be detected is detected by a change in intensity or phase of the light to be emitted or their spectral characteristics.

Furthermore, a tenth invention is an optical fiber sensor of the ninth invention, characterized in that a means for reflecting the light propagating through the core is provided on one end side of the optical fiber. As a means for this, one end of the optical fiber used in the present invention is directly coated with a dielectric multilayer film or the like so as to overlap at least a part of the core portion, and a light reflecting material is applied. Alternatively,
A system is used in which the light emitted from the optical fiber is reflected by a reflecting mirror or the like and is then coupled to the optical fiber again. Alternatively,
Material that constitutes the optical fiber (glass or polymer)
The reflection due to the difference in refractive index between the air and the surrounding air is used. Here, a plurality of holes provided “mainly” inside the clad cross section means that a part of the hole portion may be in contact with the core portion or may be a structure included in the core portion. Such holes can also satisfy the following effects. The holes are generally filled with air, but other suitable gas may be mixed or filled.

[0015]

In the optical fiber sensor of the present invention, the optical fiber of the first invention is used to sense the substance to be detected introduced therein by utilizing the seeping of light into the holes inside the core. . In this case, there is no possibility that other substances will adhere to the surface of the holes of the core where light seeps out, and the sensor can be easily managed.

If an inner layer made of a material having a relatively lower refractive index than that of the core is provided on the inner surface of the core as in the second aspect of the invention, the interface between the core and the inner layer becomes stable and the scattered light is scattered. Since it is suppressed, the loss of propagating light is reduced and the propagating light propagates longer, so that the sensing length can be adjusted. In this case, since the leaching distribution state of light changes depending on the refractive index of the inner layer, the sensing sensitivity can be adjusted.

When the outer circumference of the optical fiber is coated as in the third invention, the mechanical strength of the optical fiber can be maintained. In this case, the coating on the outer circumference of the optical fiber does not affect the sensing function, so there is no need to consider the refractive index and light transmittance of the coating material according to the sensing purpose and the surrounding environment. , The coating can be applied freely.

Further, as in the fifth invention, when a means for reflecting the light propagating through the core is provided at one end of the optical fiber,
Utilizing the reflection, light can be incident from one end of the optical fiber and detection can be performed there. In this way, light can be incident and detected at the same end of the optical fiber, and a simpler system can be assembled. In addition,
It is also possible to utilize reflection due to the difference in refractive index between the material forming the optical fiber and the surrounding air.

Further, in the optical fiber sensor of the present invention,
By using the optical fiber of the sixth invention, the light leaching into the holes provided in the clad portion of the light propagating through the core portion is used to sense the substance to be detected introduced therein. In this case, there is no possibility that other substances will adhere to the surface of the holes provided in the clad portion during storage, and the sensor can be easily managed. Further, since the holes are mainly in the clad portion and not in the core portion, it is possible to easily introduce light into the optical fiber sensor. Further, by coating the outer peripheral portion of the optical fiber with a coating material, it is possible to improve the mechanical reliability without affecting the sensing characteristics.

Here, as in the seventh invention, when three or more holes are provided mainly inside the cladding cross section, the dependence of the sensing characteristics on the polarization plane of light propagating in the core is reduced, and Sensing sensitivity can be adjusted by the number of holes. By the way, when the polarization degree of the light source is high, the distribution of the electromagnetic field has directionality according to the polarization state. At this time, if the distribution of the detection substance also has anisotropy, the detection characteristics differ depending on the polarization state. Therefore, when the number of holes is one or two, there is a strong anisotropy in the linear direction in the cross section connecting the holes and the core. Therefore, as described above, by providing three or more holes, this anisotropy is improved.

Further, as in the eighth aspect of the invention, the plurality of holes mainly provided inside the cladding cross section have substantially the same shape and size, respectively, and are substantially equal in distance from the core. When they are arranged at substantially equal intervals, the above-mentioned anisotropy can be further reduced, and the polarization dependence of the sensing characteristics can be significantly reduced, and a sensor with extremely high accuracy can be obtained.

Further, as in the tenth invention, the sixth to sixth
When a means for reflecting the light propagating through the core is provided on one end side of the optical fiber having the structure of 8 invention, the reflection is used to allow the light to enter from one end of the optical fiber and to be reflected at the incident end of the optical fiber. It is also possible to detect the emitted light. In this way, light can be incident and detected at the same end of the optical fiber, and a simpler system can be assembled.

As described above, in order to perform substance sensing using the optical fiber, one or both ends of the optical fiber are held in the substance to be detected, and the substance to be detected is introduced into the pores by a capillary phenomenon or the like. The optical fiber into which the substance to be detected is introduced is optically connected to a tester that has a mechanism for emitting and detecting light, and light is incident on the optical fiber to change the intensity of incident light due to the substance to be detected. To obtain substance information. Alternatively, while the light is incident from one end of the optical fiber, the optical fiber is held in the substance to be detected, and the light reflected at the other end of the optical fiber is detected to obtain the substance information. The optical fiber of the present invention is useful as a disposable type short length sensor.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. (Example 1) In this example, an optical fiber sensor made of a glass optical fiber was used for spectral analysis of gas. The optical fiber used was manufactured as follows. That is, as shown in FIG. 5A, a cylindrical optical fiber preform 21 having a clad 24 made of quartz glass and a core 23 made of glass whose refractive index is increased by adding Ge into quartz. To create. Then, at the center of the optical fiber preform 21, as shown in FIG.
The holes 22 are opened by a grinder. This optical fiber base material 2
1 is drawn by a normal optical fiber drawing method, and as shown in FIG.
The optical fiber 11 having a small diameter was manufactured. This optical fiber 1
A coating material 16 is applied to the periphery of 1 with an ultraviolet curable resin,
The optical fiber 11b as shown in FIG. 3 was formed. Hole 1
The diameter of 2 was 100 μm, and the outer diameter of the core 13 was 110 μm. The produced optical fiber 11b is cut into pieces each having a length of about 5 to 20 cm while the coating material 16 is still applied to form an optical fiber sensor, and both ends thereof are prevented in order to prevent dust, moisture, etc. from entering the holes 12 during storage. Was sealed with foil for sealing and stored.

In order to measure the presence or absence of the gas to be detected, the sealing foil of the optical fiber sensor was removed and the gas was held in the air stream to be measured for an appropriate time, and then this gas was analyzed by a tester. As shown in FIG. 6, the tester 41 has a white light source 42 and a spectroscope 43 for splitting the light source 42 on one side, and a photodetector 44 on the other side. The test method is as follows: the optical fiber sensor 11 between the spectroscope 43 and the photodetector 44.
c is connected via the airtight connector 45 so that gas does not leak from both ends of the optical fiber sensor 11c. Then, the light obtained by dispersing the white light is emitted from the spectroscope 43, is incident on one end of the optical fiber sensor 11c, and the emitted light from the other end is detected by the photodetector 44. By the method described above, it was possible to detect the presence or absence of methane gas. The gas to be analyzed is exchanged by holding the optical fiber sensor 11c in the gas for an appropriate time. In this case, the holding time can be shortened by reducing the pressure of the holes 12 of the optical fiber sensor 11c.

(Embodiment 2) In this embodiment, an optical fiber made of a polymer material having optical transparency is used as an optical fiber sensor to perform a spectroscopic analysis of a liquid. As the polymer material, a fluororesin type, a silicone resin type, an acrylic type, a styrene type or the like can be used. As shown in FIG. 7, the optical fiber 51 is made of a light-transparent silicone-rubber resin, and is composed of a core 53 and a clad 54 having an outer diameter of 2 mm. A hole 52 is provided. A light reflecting material 55 is applied to one end of the optical fiber 51. The clad 54 of the optical fiber 51 is not coated with a coating material.

In order to analyze the presence or absence of the liquid to be detected, one end of this optical fiber 51 was dipped in the liquid for analysis. At this time,
The central portion of the optical fiber 51 in the longitudinal direction is pinched to apply lateral pressure to constrict it, and the lateral pressure is released after being immersed in a liquid. Then, the analysis liquid is introduced into the holes 52 of the optical fiber 51 due to the change in the internal pressure of the optical fiber 51 and the capillary phenomenon. As shown in FIG. 8, the analysis liquid was analyzed by connecting the end of the optical fiber 51 where the light reflecting material 55 was not applied to the optical branching device 63 via the connector 64 and the optical guide 65. . Light was incident on the light branching device 63 from the light source 61 through the light guide 65, and the reflected light reflected by the light reflecting material 55 of the optical fiber 51 was detected by the photodetector 62 and analyzed. An effective method is also to provide a wavelength selection element such as an optical filter or a grating immediately after the light source 61 or immediately before the photodetector 62 to detect a specific wavelength or a wavelength range distribution.

Example 3 The optical fiber used in the optical fiber sensor was manufactured as follows. That is, a cylindrical optical fiber preform having a clad made of quartz glass and a core made of glass whose refractive index is increased by adding Ge into quartz is prepared. Next, a hole is made in the clad portion of the optical fiber preform by a grinder, and the optical fiber is drawn by a normal optical fiber drawing method.
As shown in (a) and (b), the outer shape 12 of the cladding 74
An optical fiber 71 of 5 μm was manufactured. Note that FIG.
(A) and (b) show two and one holes 72, respectively.
It is a cross-sectional perspective view of the optical fiber 71 provided with. A coating material 75 is applied to the periphery of the optical fiber 71 with an ultraviolet curable resin. The holes 72 had a diameter of 30 μm, and the core 73 had an outer diameter of 10 μm. The produced optical fiber 71 is a covering material 7
5 is cut to a length of about 5 to 20 cm to make an optical fiber sensor, and both ends are sealed with a sealing foil to prevent dust and water from entering the holes 72 during storage. I kept it.

Next, in order to measure the presence or absence of the dye in the liquid to be measured, the seal foil of the optical fiber sensor is removed, and a container containing methyl alcohol mixed with the dye to be measured is placed. One end of an optical fiber sensor having substantially the same length was held in a container containing the same methyl alcohol that did not mix the dye for a proper time, and a liquid was introduced into the pores by the capillary effect. After that, the test liquid was analyzed with a tester. As shown in FIG. 12, this tester 81 has a white light source 82 and a spectroscope 83 for splitting the light source on one side, and a photodetector 84 on the other side. It is the same as the tester (shown in FIG. 6). The test method is as follows.
The optical fiber 85 for light introduction is liquid-tightly connected to the spectroscope 83 and the photodetector 84. And then
The light obtained by dispersing the white light is emitted from the spectroscope 83, is incident on one end of the optical fiber sensor 71a, and the emitted light from the other end is detected by the photodetector 84. By the method described above, the presence or absence of the dye could be detected from the difference in the spectral characteristics. In addition, the optical fiber sensor 71a and the optical fiber 8 for introducing light
The optical coupling rate with No. 5 was improved to 75% or more as compared with the case of the optical fiber sensor in which holes were provided in the core. The above method can be applied to substances other than liquid.

By the way, as described above, there is no problem in using the optical fiber sensor 71a when performing a test using a white light source having a low degree of polarization. However, in the case of using laser light or performing highly accurate quantitative detection such as concentration detection, there is a problem that the sensitivity of sensing depends on the polarization state of light. Therefore, FIG.
As shown in (a) and (b), when the optical fiber 71 having three or more holes 72 in the clad portion 74 was used as an optical fiber sensor, the measurement accuracy was improved. This kind of optical fiber 71 can be manufactured by changing the number of holes at the time of grinding in the same process as the above-mentioned optical fiber 71. 10 (a) and 10 (b) are cross-sectional perspective views of the optical fiber 71 provided with four and three holes 72, respectively. Further, as shown in FIG. 11, the three holes 72 provided in the clad 74 have the same shape and size (in this case, a circle having the same inner diameter), and the holes 72 are substantially the same distance from the center of the core 73. A (in this case, on a concentric circle with the core 73 as the center) and the mutual intervals B are substantially equal. When such an optical fiber is used as an optical fiber sensor, the polarization dependence of the sensing sensitivity is significantly reduced, and a certain detection sensitivity is exhibited regardless of the polarization state of the light introduced. Note that the number of the holes 72 is not limited to three, and as shown in FIGS.
The number may be six, eight, or the like.

(Embodiment 4) FIG. 16 is a perspective view of an end portion of an optical fiber used as the optical fiber sensor of this embodiment. The optical fiber 71 is provided with a reflecting means such as a dielectric multilayer film 76 so as to cover a part or the whole of the core 73. By using this optical fiber sensor, it is possible to detect light without providing a reflection optical system. When the intensity of light is high, or when the material forming the optical fiber sensor has a high refractive index, the material forming the optical fiber sensor and the air are not provided without providing a reflecting means such as the dielectric multilayer film 76. The reflection due to the difference in the refractive index of can be used as the reflection means. In addition, as a reflection method, light emitted from the optical fiber sensor may be reflected by a reflecting mirror and then coupled to the optical fiber sensor again.
The present embodiment uses reflected light instead of detecting the light transmitted through the optical fiber sensor as in the above-described embodiment. By doing so, the applications of the optical fiber sensor can be expanded. For example, FIG.
As shown in FIG. 7, an endoscope 91 used for a gastric camera or the like.
The optical fiber sensor 71a of this embodiment is housed in
A hole 7 in the sensor optical fiber 71a for body fluid such as gastric juice.
It is possible to perform the component analysis in real time by using the light source 92, the optical fiber 93 for introducing light, the branching device 94, the spectroscope 95, the photodetector 96, the connector 97, etc., which are installed in the external unit 2 in FIG. .

[0032]

As described above, according to the present invention, there is provided an optical fiber sensor utilizing the evanescent light of the light propagating through the optical fiber, wherein the optical fiber has a light transmitting property and a relative refractive index. Of a high core material having a hole in the center and a clad made of a material having a relatively low refractive index provided on the outer periphery of the core, and introducing a substance to be detected into the hole, Since the substance to be detected is detected by the change in the intensity, phase, or their spectral characteristics of the light propagating through the core, the optical fiber can be coated freely, so that the mechanical strength can be maintained. It is effective, and because there is no possibility that other substances will adhere to the surface of the holes in the core where light leaks out, it is easy to manage the optical fiber sensor. effective.

Further, in the above invention, when the inner layer made of a material having a relatively lower refractive index than the core is provided on the inner surface of the core, the sensing sensitivity can be adjusted, and the scattering by the inner interface is prevented. Since it is suppressed and the loss can be reduced, there is an effect that the measurement length can be made longer and the sensitivity can be enhanced.

Further, in the above invention, when a means for reflecting light propagating in the core is provided at one end of the optical fiber,
Since light can be incident and detected at the same end of the optical fiber, there is an effect that sensing can be performed by assembling a simpler system depending on the application.

Further, according to the present invention, there is provided an optical fiber sensor utilizing the evanescent light of the light propagating through the optical fiber, wherein the optical fiber is made of a material having a light transmitting property and a relatively high refractive index. A core and a clad having a hole made of a material having a relatively low refractive index provided on the outer periphery of the core, and introducing a substance to be detected into the hole, the intensity of light propagating through the core, Since the substance to be detected is detected by the change of the phase or the spectral characteristic, there is an effect that the light can be easily introduced into the optical fiber sensor.

Further, in the above invention, if the number of holes provided in the clad is three or more, it is possible to reduce the influence of the polarization plane of the light propagating in the core on the sensing characteristics. In particular, when the holes have the same shape and size and are arranged at equal distances from the core, the influence of the polarization plane of light on the sensing characteristics can be further reduced.

Further, in the above invention, when a means for reflecting light propagating in the core is provided at one end of the optical fiber,
Since light can be incident and detected at the same end of the optical fiber, there is an effect that sensing can be performed by assembling a simpler system depending on the application.

[Brief description of drawings]

FIG. 1 is a sectional perspective view of an embodiment of an optical fiber according to the present invention.

FIG. 2 is a sectional perspective view of another embodiment of the optical fiber according to the present invention.

FIG. 3 is a sectional perspective view of still another embodiment of the optical fiber according to the present invention.

FIG. 4 is a cross-sectional perspective view of an optical fiber in an embodiment of the optical fiber sensor according to the present invention.

5 (a) and 5 (b) are explanatory views of a manufacturing process of an optical fiber preform used for manufacturing an embodiment of an optical fiber according to the present invention.

FIG. 6 is an explanatory diagram of a gas analysis method using the optical fiber.

FIG. 7 is a cross-sectional perspective view of an optical fiber that is another embodiment of the optical fiber sensor according to the present invention.

FIG. 8 is an explanatory diagram of a liquid analysis method using the optical fiber sensor of the above embodiment.

9A and 9B are cross-sectional perspective views of yet another embodiment of the optical fiber according to the present invention.

10A and 10B are cross-sectional perspective views of yet another embodiment of the optical fiber according to the present invention.

FIG. 11 is a cross-sectional view of still another embodiment of the optical fiber according to the present invention.

FIG. 12 is an explanatory diagram of a liquid analysis method using the optical fiber sensor of Example 3.

FIG. 13 is a cross-sectional view of yet another embodiment of the optical fiber according to the present invention.

FIG. 14 is a cross-sectional view of yet another embodiment of the optical fiber according to the present invention.

FIG. 15 is a cross-sectional view of still another embodiment of the optical fiber according to the present invention.

FIG. 16 is a sectional perspective view of still another embodiment of the optical fiber according to the present invention.

FIG. 17 is an explanatory diagram of a component analysis method using the sensor optical fiber of Example 4 in an endoscope.

FIG. 18 is an explanatory diagram of a conventional analysis method using an optical fiber.

FIG. 19 is an explanatory diagram of another analysis method using a conventional optical fiber.

FIG. 20 is an explanatory view of still another analysis method using a conventional optical fiber.

[Explanation of symbols]

11, 11a, 11b, 51, 71 Optical fiber 12, 22, 52, 72 Hole 13, 23, 53, 73 Core 14, 24, 54, 74 Cladding 15 Inner layer 16, 75 Coating material 17, 55 Light reflecting material 21 Optical fiber base material 41, 81 Tester 42, 61, 82, 92 Light source 43, 83, 95 Spectrometer 44, 62, 84, 96 Photodetector 45, 64, 97 Connector 63 Optical splitter 65 Optical guide 11c, 71a Optical fiber sensor 85, 93 Optical fiber for light introduction 86 Butt portion 91 Endoscope 94 Optical branching device

Claims (10)

[Claims] 1. An optical fiber having a core made of a material having a light transmission property and a relatively high refractive index, and a clad made of a material having a relatively low refractive index provided on the outer periphery of the core, An optical fiber characterized in that a hole is provided in the core portion. 2. The optical fiber according to claim 1, wherein an inner layer made of a material having a relatively lower refractive index than that of the core is provided on the inner surface of the hole provided in the core. 3. The optical fiber according to claim 1, wherein the outer periphery of the clad is covered with a coating material. 4. An optical fiber sensor utilizing evanescent light of light propagating through an optical fiber, wherein a substance to be detected is introduced into the holes of the optical fiber according to claim 1, and propagates through a core. An optical fiber sensor, which detects a substance to be detected by changing the intensity or phase of light or their spectral characteristics. 5. A means for reflecting the light propagating through the core is provided on one end side of the optical fiber.
The optical fiber sensor described. 6. An optical fiber having a core made of a material having a light transmitting property and a relatively high refractive index, and a clad provided on the outer periphery of the core and made of a material having a relatively low refractive index, An optical fiber mainly having holes in the cladding. 7. The optical fiber according to claim 6, wherein three or more holes are provided mainly in the cladding portion. 8. The plurality of holes mainly provided in the clad portion have substantially the same shape and size, and are arranged at substantially equal distances from the core and at substantially equal intervals from each other. The optical fiber according to claim 7, wherein 9. An optical fiber sensor utilizing evanescent light of light propagating through an optical fiber, wherein the substance to be detected is introduced into the holes of the optical fiber according to claim 6, and propagates through the core. An optical fiber sensor, which detects a substance to be detected by a change in light intensity, phase, or their spectral characteristics. 10. The optical fiber sensor according to claim 9, wherein a means for reflecting light propagating through the core is provided on one end side of the optical fiber.