JP3846088B2 - Optical fiber - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber using air as a clad, and more specifically, light source-separated illumination represented by transmission of sunlight, medical equipment illumination, microscope irradiation, in-vehicle illumination, high place illumination, etc. Further, the present invention relates to an optical fiber applied to a light guide, an image fiber, etc. in toys, ornaments and the like.
[0002]
[Prior art]
As shown in FIG. 13A, a conventional large-diameter optical fiber A is made of a flexible transparent core 1 such as soft acrylic (resin) using a material having a lower refractive index such as fluororesin. The tube 2 was covered and formed, and the tube 2 was used as a clad. The light that can be guided by the optical fiber is determined by the refractive indexes of the core and the clad, and the light incident at an angle larger than the light receiving angle θ expressed by the following equation (1) leaks through the clad.
[0003]
θ = Asin (n₀ ²-N₁ ²)^1/2  ... (1)
n₀Is the refractive index of the core, n₁Indicates the refractive index of the cladding.
[0004]
Accordingly, when the soft acrylic core 1 and the fluororesin tube 2 are used as the clads, the refractive indexes are 1.48 to 1.49 and 1.34 to 1.35, respectively, so θ is 38 °. (At this time, the critical angle α is about 65.6 °).
[0005]
In the case of an optical fiber that guides parallel light such as a laser, such as a communication optical fiber, there is no problem even if the light receiving angle θ is narrow. However, in the optical fiber A for illumination, light generated from a substantially point light source. Therefore, if the light receiving angle θ is narrow, the utilization efficiency of the light generated from the light source is lowered.
[0006]
That is, in the illumination optical fiber system as shown in FIG. 13B in which the light source 61 is disposed in front of the concave reflector 60 and the light generated by the light source 61 is guided by the optical fiber A, The optical fiber A is disposed in front of the light source 61, and the end of the optical fiber A is disposed at a position facing the light source 61, that is, on the optical axis of the reflection system such as the light source 61 and the reflection plate 60, and is reflected. The light a reflected at the end of the plate 60 is arranged at a position where it enters the end of the optical fiber A at a light receiving angle θ. Accordingly, the light b passing between the end of the reflecting plate 60 and the optical fiber A is not incident on the optical fiber A as lost light. However, in order to improve the light utilization efficiency, the reflecting plate 60 is enlarged. Even if this light b was reflected and made incident on the end of the optical fiber A (this light is indicated by c), it was not guided because it was incident at an angle larger than the light receiving angle θ.
[0007]
Accordingly, there is provided an optical fiber A that uses air or a material having a low refractive index comparable to air for the clad so that the light receiving angle θ is theoretically 90 ° and can take in more light. The present applicant has filed an application as Japanese Patent Application No. 10-332120. By using this optical fiber A, it is expected that a significant improvement in incident efficiency can be obtained and that the light utilization efficiency can be improved.
[0008]
In this optical fiber A, as shown in FIG. 14A, the transparent core 1 having a circular or elliptical cross section and having flexibility has an inner diameter larger than the outer diameter of the core 1 and has flexibility. The air layer 3 is interposed as a cladding between the outer peripheral surface of the core 1 and the inner peripheral surface of the tube 2, and both ends of the core 1 and the tube 2 are caulked and fixed by sleeves 50. It is what.
[0009]
[Problems to be solved by the invention]
However, the optical fiber A using air as a cladding has the following problems.
[0010]
(1) In the optical fiber system for illumination, as shown in FIG. 13B, light is incident on the optical fiber A from its end portion. In this optical system (illumination optical fiber system), the optical fiber A In order to efficiently collect light at the end, the reflector 60 or the like is used to concentrate the light within the smallest possible area. Therefore, if the center of the optical fiber A (the center of the core 1, the air layer 3, and the tube 2) is deviated from the center of light collection, the light that does not enter the core 1 increases rapidly, leading to a decrease in light collection efficiency. There was a problem.
[0011]
In the optical fiber A shown in FIG. 14A, since the fixing is performed by holding the outer peripheral surface of the tube 2 or the sleeve 50, the positional relationship between the optical axis and the outer peripheral surface of the tube 2 or the sleeve 50 can be fixed. It is. However, since the core 1 and the tube 2 are both flexible, the center of the core 1 and the center of the tube 2 as shown in FIG. The center of the tube 2 or the center of the sleeve 50 may not always coincide with the center of the core 1 due to a deviation from the center of the sleeve 50 or an inclination of the end face of the core 1. Therefore, even if the optical fiber A is installed with reference to the outer circumference of the tube 2 or the sleeve 50, the center of the core 1 may not coincide with the optical axis, and the amount of light incident on the core 1 is reduced and the light collection efficiency is reduced. There was a problem that decreased.
[0012]
(2) A major feature of the optical fiber A shown in FIG. 14 (a) is that the outer periphery of the core 1 is always in contact only with air having a refractive index of 1.0. Since the inner diameter of the tube 2 is larger than the outer diameter of the core 1 in the places other than the caulking portions at both ends, the core 1 does not come into contact with the tube 2, and the light guide property is not lowered due to the contact between the core 1 and the tube 2. Absent. However, when the caulking is incomplete, dust intrusion into the tube 2, dust adhesion to the core 1, moisture intrusion and dew condensation in the tube 2 occur. As a result, the core 1 has an outer peripheral surface. There is a problem that light having a refractive index higher than that of air adheres and light is scattered on the outer peripheral surface of the core 1 or leaks through the tube 2 to impair the light guide property.
[0013]
(3) In the optical fiber A shown in FIG. 14A, since the core 1 and the tube 2 are in close contact with each other in the caulking portion, even if the tube 2 has a relatively low refractive index such as a fluororesin, the caulking portion The critical angle is larger than that of air, and light tends to leak from the caulked portion. Further, since a large force is applied for caulking, the flexible core 1 is deformed into a concave shape, and thus light easily leaks from the caulking portion. As a result, there is a problem that the light guide efficiency is lowered.
[0014]
The present invention has been made in view of the above points, and provides an optical fiber capable of preventing a decrease in light guide efficiency without reducing light collection efficiency and without impairing light guide performance. It is intended to do.
[0015]
[Means for Solving the Problems]
  In the optical fiber A according to claim 1 of the present invention, the transparent core 1 having a circular or elliptical cross section and having flexibility has an inner diameter larger than the outer diameter of the core 1 and has flexibility. In the optical fiber A that is disposed in the air layer 3 between the outer periphery of the core 1 and the inner periphery of the tube 2,The cap 4 is formed of a hard transparent material having a refractive index similar to that of the core 1,Caps 4 are provided at both ends of the tube 2 so that the center of the core 1 is fixed in the vicinity of the center of the tube 2 and the inside of the tube 2 is substantially sealed, and a cylindrical shape having substantially the same shape as the outer diameter of the core 1. The insertion portion 5 formed on the cap 4 is provided in the cap 4, the insertion portion 5 is inserted into the gap between the core 1 and the tube 2, and the outer periphery of the tube 2 outside the insertion portion 5 is tightened and fixed.In addition, at the interface between the outer surface of the insertion portion 5 and the inner surface of the tube 2, at least a lower refractive material than the tube 2 or a member whose inner surface is a mirror surface is provided.It is characterized by this.
[0017]
  Further, in the optical fiber A according to claim 2 of the present invention, in addition to the configuration of claim 1, the outer diameter of the insertion portion 5 is the inner diameter of the tube 2.Smaller thanIt is characterized by this.
[0018]
  Claims of the invention3The optical fiber A according to claim 1Or 2In addition to the configuration, the end portion of the cap 4 facing the insertion portion 5 is a transparent window member 6.
[0021]
  Claims of the invention4The invention according to claim 1 to claim 13In addition to any of the configurations described above, the surface of the cap 4 that contacts the outer peripheral surface of the core 1 is a mirror surface.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0026]
The core 1 can be made of a transparent transparent polymer such as methacrylic resin or acrylic resin. The molecular structure of the monomer used as a raw material for this polymer is not particularly limited, but the polymer forming the core 1 has a flexural modulus of 100 kg / mm.²The following viscoelastic body is preferable. The bending elastic modulus of the core 1 is 100 kg / mm²When the optical fiber A is formed with the core 1 having a diameter of about 1 mm or less, the core 1 having a diameter of several mm or more used in light transmission can be used. In the case of the optical fiber A using the optical fiber A, it cannot be bent easily, and there is a possibility that it will be broken if it is forced to bend. Although the lower limit of the bending elastic modulus is not particularly set, the bending elastic modulus of the core 1 is 0.5 kg / mm.²If it is less than that, deformation due to its own weight cannot be ignored, and the core 1 is held in the tube 2 in a non-contact state when the core 1 is inserted into the tube 2 to produce the optical fiber A as will be described later. This is a practical lower limit.
[0027]
Moreover, as another characteristic of the polymer which forms the core 1, it is preferable that a glass transition temperature is 80 degrees C or less. When the glass transition temperature of the core 1 is 80 ° C. or lower, the above-described bending elastic modulus of the core 1 can be maintained even by a temperature change under a normal environment in which the optical fiber A is used. If the temperature exceeds 80 ° C., the flexural modulus may be higher than the above along with the temperature change. The lower limit of the glass transition temperature of the core 1 is not particularly set, but −10 ° C. is a practical lower limit.
[0028]
The core 1 is not formed into a shape having a corner like a polygonal cross section, but is formed into a circular cross section (perfect circle) or a cross section ellipse so as to have a smooth curved outer peripheral surface. is there. If there is a corner in the cross-sectional shape of the core 1, light leakage occurs at the edge, and the light transmission efficiency (light guide efficiency) decreases. In order to further suppress light leakage due to the outer peripheral shape of the core 1, it is preferable that the average roughness Ra of the outer peripheral surface of the core 1 is 0.05 μm or less. When the surface average roughness Ra of the outer peripheral surface of the core 1 exceeds 0.05 μm, irregular reflection occurs at the interface of the outer peripheral surface of the core 1 and light leakage may occur, which may slightly affect the decrease in optical transmission efficiency. Of course, the surface average roughness Ra of the outer peripheral surface of the core 1 is preferably as small as possible. Ideally, the surface average roughness Ra is preferably zero.
[0029]
The manufacturing method of the core 1 is not limited at all. For example, a monomer is cast in a fluororesin tube having a desired inner surface shape and inner surface smoothness, and is polymerized by heating or ultraviolet irradiation. A method of obtaining the core 1 by demolding from a fluororesin tube after polymerization is generally performed.
[0030]
On the other hand, the tube 2 is made of a polymer (resin) having an elasticity enough to follow and bend the core 1 without causing extreme wrinkles or breakage in the bendable range of the core 1. It is preferable to use one having a refractive index of light smaller than that of the core 1. Specific examples of this polymer include polyethylene, polypropylene, silicone rubber, and fluorine-based polymers. Among them, the refractive index is lower, the deformation due to stress in handling is smaller, and the inner peripheral surface described later. Fluoropolymers are preferred from the standpoint of easy processing to achieve surface smoothness. The tube 2 is formed so that the inner diameter is larger than the outer diameter of the core 1, and the inner peripheral surface cross-sectional shape of the tube 2 is preferably formed in the same shape as the outer peripheral surface cross-sectional shape of the core 1.
[0031]
  And shown in FIG.Reference exampleIn the optical fiber A, the core 1 is disposed in the tube 2 by inserting the core 1 into the tube 2 having both ends open, and the cap 4 is attached to the opening at the end of the tube 2. Is formed. The cap 4 can be provided at both ends of the tube 2. By disposing the core 1 in the tube 2 in this way, the air layer 3 is formed between the outer peripheral surface of the core 1 and the inner peripheral surface of the tube 2. An optical fiber A having a cap 4 at the part can be produced.
[0032]
The cap 4 includes an annular holding portion 21, a window member 6 formed on the inner side of the holding portion 21, and a substantially cylindrical insertion portion formed integrally with the holding portion 21 so as to protrude rearward from the window member 6. And 5. The window material 6 is formed of a transparent and hard acrylic resin having a refractive index equivalent to that of the core 1 or a transparent glass or resin close to the refractive index of the core 1, and is formed so as not to be easily deformed even when an external force is applied. Yes. The plate-like window material 6 can be fitted inside the holding portion 21 and held to form the cap 4, and the opposite end of the cap 4 opposite to the insertion portion 5 is formed of the transparent window material 6. Will be. The holding portion 21 and the insertion portion 5 are formed of a metal or resin that does not easily deform even when an external force is applied, and the insertion portion 5 is formed to have a uniform thickness over the entire circumference. Further, the centers of the holding portion 21, the insertion portion 5, and the window material 6 are formed so as to substantially match.
[0033]
The inner peripheral shape of the insertion portion 5 is formed substantially the same as the outer peripheral shape of the core 1, and the inner diameter of the insertion portion 5 is formed substantially the same as the outer diameter of the core 1. That is, the insertion portion 5 can be inserted without applying much stress to the core 1, and when inserted, the outer peripheral surface (side surface) of the core 1 and the inner peripheral surface (side surface) of the insertion portion 5 are in close contact with each other. It is preferable to form the inner peripheral shape and the inner diameter. The outer peripheral shape of the insertion portion 5 is formed substantially the same as the inner peripheral shape of the tube 2, and the outer diameter of the insertion portion 5 is formed substantially the same as the inner diameter of the tube 2. That is, it is preferable that the insertion portion 5 is formed in an outer peripheral shape and an outer diameter such that no gap is generated between the inner peripheral surface (side surface) of the tube 2 and the outer peripheral surface of the insertion portion 5 when inserted. As long as the tube 2 has some elasticity, the outer diameter of the insertion portion 5 may be larger than the inner diameter of the tube 2 as long as the cap 4 can be inserted.
[0034]
The inner peripheral surface of the insertion portion 5 may be a mirror surface capable of reflecting light, such as an aluminum vapor deposition film or a silver vapor deposition film, and this allows the outer peripheral surface of the core 1 and the inner peripheral surface of the insertion portion 5 to be reflected. Light leakage at the contact portion can be prevented, and the light guide efficiency of the optical fiber A can be improved. Further, the entire cap 4 may be formed of the material of the window material 6, and the window material 6, the holding portion 21, and the insertion portion 5 may be integrated.
[0035]
When attaching the cap 4 to the end portion of the tube 2, the insertion portion 5 of the cap 4 is inserted into the gap (air layer 3) between the end portion of the core 1 and the end portion of the tube 2. A ring spring 25 is fitted on the surface of the tube 2, and the end portion of the core 1, the end portion of the tube 2, and the insertion portion 5 are uniformly tightened and fixed over the entire circumference by the elastic force of the ring spring 25. At this time, the end portion of the tube 2 and the back surface of the holding portion 21 are brought into close contact with each other, the outer peripheral surface of the core 1 and the inner peripheral surface of the insertion portion 5 are brought into close contact, and the outer peripheral surface of the insertion portion 5 and the inner peripheral surface of the tube 2 are connected. Further, the surface of the window material 6 on the core 1 side is adhered to the end surface of the core 1. The surface of the window material 6 on the core 1 side and the end surface of the core 1 may be bonded with an acrylic or glass-based transparent adhesive, which can improve the adhesion. Further, instead of the cap ring spring 25, another jig that can be tightened by a surface with an appropriate force may be used.
[0036]
And by attaching the cap 4 to the end portion of the tube 2 in this way, the insertion portion 5 having a uniform thickness is interposed between the end portion of the core 1 and the end portion of the tube 2, The center of the core 1 is fixed near the center of the tube 2. That is, the centers of the core 1, the tube 2, and the air layer 3 are substantially coincident and the core 1 and the tube 2 are disposed concentrically. This state is caused by static friction with the insertion portion 5 of the cap 4. It will be retained. In addition, the centers of the core 1, the tube 2, the air layer 3, the holding portion 21, the window material 6, and the insertion portion 5 are arranged so as to substantially match. Further, the inside of the tube 2 is substantially sealed by the cap 4.
[0037]
In the optical fiber A, the cap 4 is fixed so that the center of the core 1 is fixed near the center of the tube 2 at both ends, that is, the cap 4 is fixed so that the center of the core 1 is fixed near the center of the optical fiber A. When the optical system as shown in FIG. 13B is formed, the cap 4 is positioned and fixed with respect to the optical axis of the reflection system such as the light source and the reflection plate. Axis alignment can be performed easily and stably, that is, the end surface of the core 1, the centers of the tube 2 and the air layer 3, and the optical axis can be easily and stably aligned with each other. The incident light quantity can always be kept at a maximum and stable state so as not to be lowered, the reduction of the light collection efficiency can be prevented, and the optical quality can be improved.
[0038]
Further, in the above optical fiber A, the cap 4 is provided at both ends so that the inside of the tube 2 is substantially sealed, so that dust enters the tube 2 and dust adheres to the core 1 and inside the tube 2. It is possible to prevent moisture from entering and condensing on the surface of the core 1 and preventing light from being scattered on the surface of the core 1 due to dust, moisture, etc. (light guiding loss occurs). Not). In addition, since the outer peripheral surface of the core 1 and the inner peripheral surface of the insertion portion 5 and the inner peripheral surface of the tube 2 and the outer peripheral surface of the insertion portion 5 are brought into contact with each other and tightened into a planar shape (or a plurality of lines) by the ring spring 25, the tube 2 It is possible to increase the internal sealing performance of the. Further, even when the cap 4 is tightened with a ring spring, the end of the core 1 can be protected by the insertion portion 5 so as not to be deformed, and light leakage due to deformation of the core 1 is eliminated, so that the light guide efficiency is not lowered. It can be made.
[0039]
  The other in FIG.Reference exampleIndicates. thisReference exampleThe core 1 and the tube 2 are the same as described above. As shown in FIG. 2A, the cap 4 of this reference example is the same as the cap 4 of FIG. 1 except that the cylindrical cover portion 30 is integrally provided on the holding portion 21 outside the insertion portion 5 to cover the insertion portion 5. The part 30 is formed in a double structure. The cover 30 is made of metal or the like so that it can be deformed by caulking. The insertion portion 5 and the cover portion 30 are formed to have the same length, and an insertion recess 34 that opens in an annular shape is formed between the outer peripheral surface of the insertion portion 5 and the inner peripheral surface of the cover portion 30. Further, the outer diameter of the insertion portion 5 is formed smaller than the inner diameter of the tube 2. Furthermore, the inner diameter of the cover portion 30 is substantially the same as the outer diameter of the tube 2, and the inner peripheral shape of the cover portion 30 is substantially the same as the outer peripheral shape of the tube 2. The center of the cover part 30 is substantially coincident with the centers of the insertion part 5 and the window member 6 and is arranged concentrically. Other configurations are the same as those of the cap 4 of FIG.
[0040]
  Then, as shown in FIG. 2 (b), the end of the tube 2 is fitted into the insertion recess 34 inside the cover 30 of the cap 4, and the end of the core 1 is inserted into the insertion portion 5, and thereafter A part of the cover 30 is caulked and deformed inward over the entire circumference to form a protrusion 28 that protrudes inward, and a part of the end of the tube 2 is formed over the entire periphery by the protrusion 28. By deforming inwardly to form the protrusion 29 and pressing the protrusion 29 to the entire circumference of the outer peripheral surface of the insertion portion 5, the end of the core 1 and the tube 2 can be formed without using a jig such as a ring spring. The end portion and the insertion portion 5 of the cap 4 can be fixed. Other configurations are shown in FIG.Reference exampleIt is formed in the same way.
[0041]
  thisReference exampleThen, the end of the core 1 and the end of the tube 2 are fixed by caulking.Reference exampleCompared with, a jig such as a ring spring is not required, and the number of components can be reduced and the device can be formed at low cost.
[0042]
  The other in FIG.Reference exampleIndicates. thisReference exampleThe core 1 and the tube 2 are the same as described above. As shown in FIG.Reference exampleThe cap 4 is formed by making the length of the insertion portion 5 longer in the longitudinal direction of the core 1 and the tube 2 than the length of the covering portion 30 in the cap 4 of FIG. And in FIG.Reference exampleIn the same manner, the cover 30 of the cap 4 is crimped to fix the end of the core 1 and the end of the tube 2, and then the outer peripheral surface of the cover 30 and the outer peripheral surface of the tube 2 in the vicinity of the cover 30. The adhesive tape 40 is affixed over and the tube 2 is fastened with the adhesive tape 40 so that the inner peripheral surface of the tube 2 is brought into close contact with the outer peripheral surface of the insertion portion 5. Other configurations are shown in FIGS.Reference exampleIt is formed in the same way.
[0043]
  thisReference exampleThen, since the length of the insertion portion 5 is formed longer, the portion where the core 1 and the insertion portion 5 are in close contact with each other is longer, and the sealing performance can be made higher than that of FIG. By adhering the adhesive tape 40 across the surface and the outer peripheral surface of the tube 2, the gap formed by caulking deformation on the cover portion 30 and the outer peripheral surface of the tube 2 is covered with the adhesive tape 40, and is sealed more than that of FIG. 2. Further, the inner peripheral surface of the tube 2 and the outer peripheral surface of the insertion portion 5 are brought into close contact with each other by tightening the adhesive tape 40, so that the sealing performance can be made higher than that in FIG. 2 can reliably prevent dust intrusion and dust from adhering to the core 1, moisture intrusion into the tube 2, and dew condensation, and reliably reduce light guiding properties (light guiding loss). What can be prevented A.
[0044]
  The other in FIG.Reference exampleIndicates. thisReference exampleThe core 1 and the tube 2 are the same as described above. As shown in FIG.Reference exampleThe cap 4 is formed without using the window material 6 in the cap 4 of FIG. Further, the outer diameter of the insertion portion 5 is formed substantially the same as the inner diameter of the tube 2. 2, the end portion of the tube 2 is fitted into the insertion recess 34 inside the cover portion 30 of the cap 4 and the end portion of the core 1 is inserted into the insertion portion 5. As shown in b), the end portion of the core 1, the end portion of the tube 2, and the insertion portion 5 of the cap 4 can be fixed by caulking. 4C, the outer peripheral surface of the insertion portion 5 and the inner peripheral surface of the tube 2 are bonded with an adhesive 8, whereby the end of the core 1, the end of the tube 2, and the insertion of the cap 4 are performed. The part 5 can be fixed. Further, as shown in FIG. 4 (d), by sticking the adhesive tape 40 across the outer peripheral surface of the cover 30 and the outer peripheral surface of the tube 2, the end of the core 1, the end of the tube 2, and the cap 4 The insertion part 5 can be fixed. At this time, the core 1 is fixed to the cap 4 by a static frictional force between the outer peripheral surface of the core 1 and the inner peripheral surface of the insertion portion 5. The end surface of the core 1 is disposed so as to be substantially flush with the end surface of the cap 4. Other structures are formed in the same manner as in FIGS.
[0045]
  thisReference exampleThen, since the window member 6 formed of a separate member is not provided on the cap 4, it can be formed at low cost, and light is directly incident on the core 1 without the window member 6. 6, the light is not attenuated, and the incidence efficiency can be improved.
[0046]
  In FIG.The present inventionAn embodiment of the present invention will be described. In this embodiment, the core 1 and the tube 2 are the same as described above. The cap 4 includes a window material 6 and an insertion portion 5. The window material 6 is formed of a transparent acrylic resin having a refractive index equivalent to that of the core 1 or a transparent glass or resin close to the refractive index of the core, and is formed so as not to be easily deformed even when an external force is applied. Moreover, the outer peripheral surface (side surface) of the window material 6 is formed smoothly. The outer peripheral shape of the window member 6 is formed substantially the same as the inner peripheral shape of the tube 2, and the outer diameter of the window member 6 is substantially the same as the inner diameter of the tube 2 or slightly smaller than the inner diameter of the tube 2. . That is, the window material 6 can be inserted without applying stress to the tube 2, and when inserted, no gap is generated between the inner peripheral surface (side surface) of the tube 2 and the outer peripheral surface of the window material 6. It is preferable that the outer peripheral shape and the outer diameter be formed. Further, the cross-sectional area of the window material 6 is formed larger than the cross-sectional area of the core 1.
[0047]
  The insertion portion 5 is formed in a cylindrical shape with a hard metal such as aluminum, and is bonded to one end face of the window member 6 with an adhesive. As the insertion portion 5, an acrylic resin pipe having the same refractive index as that of the core 1 can be used. The inner peripheral shape of the insertion portion 5 is formed substantially the same as the outer peripheral shape of the core 1, and the inner diameter of the insertion portion 5 is formed substantially the same as the outer diameter of the core 1. That is, the insertion portion 5 can be inserted without applying much stress to the core 1, and when inserted, the outer peripheral surface (side surface) of the core 1 and the inner peripheral surface (side surface) of the insertion portion 5 are in close contact with each other. It is preferable to form the inner peripheral shape and the inner diameter. The outer peripheral shape of the insertion portion 5 is substantially the same as the inner peripheral shape of the tube 2, and the outer diameter of the insertion portion 5 is the same as that of the window portion 6.DiameterIt is slightly smaller. That is, it is preferable that the insertion portion 5 is formed in an outer peripheral shape and an outer diameter such that no gap is generated between the inner peripheral surface (side surface) of the tube 2 and the outer peripheral surface of the insertion portion 5 when inserted. The inner peripheral surface of the insertion portion 5 may be a mirror surface of an aluminum vapor deposition film or a silver vapor deposition film capable of reflecting light, whereby the contact between the outer peripheral surface of the core 1 and the inner peripheral surface of the insertion portion 5 is achieved. Light leakage at the portion can be prevented, and the light guide efficiency of the optical fiber A can be improved.
[0048]
The optical fiber A shown in FIG. 5 has the core 1 inserted into the tube 2 from one of the openings into the tube 2 having both ends open, and the core 1 is disposed in the end of the tube 2. A cap 4 is attached. The cap 4 can be provided at both ends of the tube 2. By disposing the core 1 in the tube 2 in this way, the air layer 3 is formed between the outer peripheral surface of the core 1 and the inner peripheral surface of the tube 2. An optical fiber A having a cap 4 at the part can be produced.
[0049]
In attaching the cap 4 to the end of the tube 2, first, silica airgel 41 having a refractive index equivalent to that of air is applied to the outer peripheral surface in the vicinity of the bonding portion between the insertion portion 5 and the window material 6, and the cap 4 is attached. After that, the outer peripheral surface of the window material 6 is equivalent to being covered with the air layer 3. A similar effect can be obtained by covering a sheet whose inner surface is a mirror surface with an aluminum vapor deposition film or a silver vapor deposition film instead of the silica airgel 41 so as to adhere to the outer circumferential surface of the window material 6. Next, the end portion of the tube 2 is made to protrude slightly from the end portion of the core 1, the insertion portion 5 of the cap 4 is inserted into the gap between the end portion of the core 1 and the end portion of the tube 2, and the tube 2 The window material 6 is inserted into the protruding portion, and approximately half of the window material 6 is protruded from the end of the tube 5. Next, a ring spring 25 is fitted on the surface of the tube 2 outside the cap 4, and the end of the core 1, the end of the tube 2, and the cap 4 are uniformly tightened over the entire circumference by the elastic force of the ring spring 25. And fix. At this time, the outer peripheral surface of the core 1 and the inner peripheral surface of the insertion portion 5 are brought into close contact with each other, and the outer surface of the insertion portion 5 and the inner peripheral surface of the tube 2 are brought into close contact with each other through the silica airgel 41. The surface on the 1 side is brought into close contact with the end surface of the core 1. The surface of the window material 6 on the core 1 side and the end surface of the core 1 may be bonded with an acrylic or glass-based transparent adhesive, which can improve the adhesion. Further, instead of the cap ring spring 25, another jig that can be tightened by a surface with an appropriate force may be used.
[0050]
And by attaching the cap 4 to the end portion of the tube 2 in this way, the insertion portion 5 having a uniform thickness is interposed between the end portion of the core 1 and the end portion of the tube 2, The center of the core 1 is fixed near the center of the optical fiber A, and the center of the core 1 is fixed near the center of the tube 2. That is, the centers of the core 1, the tube 2, and the air layer 3 are substantially coincident and the core 1 and the tube 2 are disposed concentrically. This state is caused by static friction with the insertion portion 5 of the cap 4. It will be retained. In addition, the centers of the core 1, the tube 2, the air layer 3, the window material 6, and the insertion portion 5 are arranged so as to substantially match. Further, the inside of the tube 2 is substantially sealed by the cap 4. Therefore, it has the same effect as the optical fiber A shown in FIG.
[0051]
In this embodiment, the outer diameter of the window member 6 is made larger than the outer diameter of the core 1, the sectional area of the window member 6 is made larger than the sectional area of the core 1, and the outer peripheral surface of the window member 6 is formed. As shown in FIG. 5 (b), the end surface of the window member 6 outside the end surface of the core 1 is covered with a mirror surface of the silica airgel 41 having a refractive index substantially equal to that of air or an aluminum deposited film or a silver deposited film. When light enters from the area increasing portion B, the light (incident light beam) incident on the window material 6 becomes larger (more) than the light incident on the end surface of the core 1 and the area of the end surface of the window material 6 increases. Since most of the light d incident from the portion B is reflected by the outer peripheral surface of the window member 6, the light d enters the end surface of the core 1 without leaking light. Therefore, a larger amount of incident light can be obtained than that directly incident from the end face of the core 1 as shown in FIG.
[0052]
FIG. 6 shows another embodiment. In this embodiment, the core 1 and the tube 2 are the same as described above. Further, as the cap 4 in FIG. 5, an insertion portion 5 made of the same material as the window material 6 and integrally formed with the window material 6 is used. Further, when the cap 4 is attached to the end portion of the tube 2, the airgel 41 or a mirror sheet disposed between the cap 4 and the tube 2 is disposed so as to cover the outer peripheral surface of the insertion portion 5.
[0053]
This embodiment has the same effect as the embodiment of FIG. In addition, as shown in FIG. 6B, the light e which has entered the end surface area B of the window member 6 and has not entered the end surface of the core 1 is also reflected outside the peripheral surface of the insertion portion 5. Since the light enters the core 1 from the outer peripheral surface of the core 1, the incident efficiency can be further improved.
[0054]
  In FIG.Reference exampleIndicates. thisReference exampleThe core 1 and the tube 2 are the same as described above. The cap 4 is made of a transparent and hard acrylic resin having a refractive index equivalent to that of the core 1 and is formed in a substantially cylindrical shape so that it does not easily deform even when an external force is applied. Moreover, the outer peripheral surface (side surface) and end surface of the cap 4 are formed smoothly. Further, the outer peripheral shape of the cap 4 is formed in a tapered shape in which the outer diameter becomes smaller at one end, the end of the maximum diameter of the cap 4 is formed substantially the same as the inner peripheral shape of the tube 2 and the maximum of the cap 4 is formed. The outer diameter is approximately the same as or slightly smaller than the inner diameter of the tube 2. The inner peripheral shape of the cap 4 is substantially the same as the outer peripheral shape of the core 1 and is formed smoothly, and the inner diameter of the cap 4 is substantially the same as the outer diameter of the core 1.
[0055]
In the optical fiber A shown in FIG. 7, the core 1 is inserted into the tube 2 from one of the openings into the tube 2 having both ends open, and the core 1 is disposed in the tube 2. A cap 4 is attached. The cap 4 can be provided at both ends of the tube 2. By disposing the core 1 in the tube 2 in this way, the air layer 3 is formed between the outer peripheral surface of the core 1 and the inner peripheral surface of the tube 2. An optical fiber A having a cap 4 at the part can be produced.
[0056]
In attaching the cap 4 to the end of the tube 2, first, silica airgel 41 having a refractive index equivalent to that of air is applied to the outer peripheral surface of the cap 4, and the outer peripheral surface of the cap 4 is the air layer 3 even after the cap 4 is attached. Equivalent to being covered. The same effect can be obtained by covering a sheet whose inner surface is a mirror surface with an aluminum vapor deposition film or a silver vapor deposition film instead of the silica airgel 41 so as to be in close contact with the outer circumferential surface of the cap 4. Next, the cap 4 is inserted into the gap between the end of the core 1 and the end of the tube 2, and the end of the tube 2, the end of the core 1, and the end surface of the cap 4 are substantially flush. At this time, the core 1, the tube 2, and the cap 4 are tightened so that the outer peripheral surface of the core 1 and the inner peripheral surface of the cap 4 are in close contact with each other, and the outer surface of the cap 4 and the inner peripheral surface of the tube 2 are interposed via the silica airgel 41. Adhere. Further, the inner peripheral surface of the cap 4 and the outer peripheral surface of the core 1 are bonded and fixed with a transparent adhesive 8 (for example, an acrylic transparent adhesive) having the same refractive index as that of the core 1 so that the core 1 and the cap 4 have an integral structure. To form. In addition, a ring spring is fitted on the surface of the tube 2 outside the cap 4, and the end of the core 1, the end of the tube 2, and the cap 4 are uniformly tightened and fixed over the entire circumference by the elastic force of the ring spring. Also good.
[0057]
By attaching the cap 4 to the end portion of the tube 2 in this way, the cap 4 is interposed between the end portion of the core 1 and the end portion of the tube 2 so that the center of the core 1 is The center of the core 1 is fixed near the center of the tube 2 by being fixed near the center of the optical fiber A. That is, the centers of the core 1, the tube 2, and the air layer 3 substantially coincide with each other so that the core 1 and the tube 2 are disposed concentrically, and this state is maintained by the static friction of the insertion portion 5 of the cap 4. It is what is done. In addition, the centers of the core 1, the tube 2, the air layer 3, and the cap 4 are arranged so as to substantially match. Further, the inside of the tube 2 is substantially sealed by the cap 4. Therefore, it has the same effect as the optical fiber A shown in FIG.
[0058]
  Also thisReference exampleThen, in order for light to enter from the end surface of the cap 4 and to cover the outer peripheral surface of the cap 4 with the mirror surface of the silica airgel 41 having a refractive index substantially equal to air or an aluminum vapor deposition film or a silver vapor deposition film, Most of the light incident on the end surface of the cap 4 is reflected by the outer peripheral surface of the cap 4 and is not leaked to the inside from the outer peripheral surface of the core 1. It will be incident. Therefore, a larger amount of incident light can be obtained than that directly incident from the end face of the core 1 as shown in FIG. In addition, since the configuration is simpler than that shown in FIGS.
[0059]
  The other in FIG.Reference exampleIndicates. A window material 6 is provided instead of the cap 4 of the optical fiber A shown in FIG.Reference exampleThe core 1 and the tube 2 are the same as described above. The window material 6 is formed of a transparent acrylic resin having a refractive index equivalent to that of the core 1 or a transparent glass or resin close to the refractive index of the core, and is formed so as not to be easily deformed even when an external force is applied. Moreover, the outer peripheral surface (side surface) of the window material 6 is formed smoothly. The outer peripheral shape of the window material 6 is formed substantially the same as the inner peripheral shape of the tube 2. Further, the outer diameter of the window member 6 is formed to be substantially the same as or slightly smaller than the inner diameter of the tube 2 and larger than the outer diameter of the core 1. That is, the window material 6 can be inserted without applying stress to the tube 2, and no gap is generated between the inner peripheral surface (side surface) of the tube 2 and the outer peripheral surface of the window material 6 when inserted. It is preferable to form the outer peripheral shape and the outer diameter. Further, the cross-sectional area of the window material 6 is formed larger than the cross-sectional area of the core 1.
[0060]
The optical fiber A shown in FIG. 8 has the core 1 inserted into the tube 2 from one of the openings in the tube 2 having both ends open, and the core 1 is disposed in the end of the tube 2. The window material 6 is attached and formed. The window material 6 can be provided at both ends of the tube 2. By disposing the core 1 in the tube 2 in this way, the air layer 3 is formed between the outer peripheral surface of the core 1 and the inner peripheral surface of the tube 2. An optical fiber A having a window material 6 in the part can be produced.
[0061]
In attaching the window material 6 to the end of the tube 2, first, silica airgel 41 having a refractive index equivalent to that of air is applied to the outer peripheral surface of the window material 6, and the outer peripheral surface of the window material 6 is attached after the window material 6 is installed. The state is equivalent to being covered with the air layer 3. A similar effect can be obtained by covering a sheet whose inner surface is a mirror surface with an aluminum vapor deposition film or a silver vapor deposition film instead of the silica airgel 41 so as to adhere to the outer circumferential surface of the window material 6. Next, the end portion of the tube 2 is slightly protruded from the end portion of the core 1, and the window material 6 is inserted into the protruding portion of the tube 2. Next, a ring spring 25 is fitted on the surface of the tube 2 outside the window material 6, and the end of the core 1, the end of the tube 2, and the window material 6 are made uniform over the entire circumference by the elastic force of the ring spring 25. Tighten to and fix. At this time, silica airgel 41 is interposed so that the outer peripheral surface of window member 6 and the inner peripheral surface of tube 2 are brought into close contact with each other, the core 1 side surface of window member 6 is brought into close contact with the end surface of core 1 and the core of window member 6. The surface on the one side and the end surface of the core 1 are bonded with an acrylic or glass-based transparent adhesive 8. Further, instead of the cap ring spring 25, another jig that can be tightened by a surface with an appropriate force may be used. Further, even if the length of the tube 2 is adjusted so that approximately half of the window member 6 protrudes from the end of the tube 2 and the vicinity of the end of the tube 2 and the protruding portion of the window member 6 are adhered and fixed with an adhesive tape. good.
[0062]
Then, by attaching the window material 6 to the end portion of the tube 2 in this way, the end portion of the core 1 and the end portion of the tube 2 are fixed to the window material 6, and the center of the core 1 is light. The center of the core 1 is fixed near the center of the tube 2 while being fixed near the center of the fiber A. That is, the centers of the core 1, the tube 2, and the air layer 3 are substantially matched so that the core 1 and the tube 2 are disposed concentrically, and this state is maintained by the window material 6. In addition, the centers of the core 1, the tube 2, and the window material 6 are arranged so as to substantially coincide with each other. Further, the inside of the tube 2 is in a state of being substantially sealed by the window material 6. Therefore, the window material 6 is provided instead of the cap 4 of the optical fiber A shown in FIG. 1, and the same effect as that of the optical fiber A shown in FIG.
[0063]
  Also thisReference exampleThen, the outer diameter of the window member 6 is made larger than the outer diameter of the core 1, the sectional area of the window member 6 is made larger than the sectional area of the core 1, and the outer peripheral surface of the window member 6 is substantially equal to air. In order to cover with the silica airgel 41 having a refractive index, light is incident from the area increasing portion of the end face of the window member 6 outside the end face of the core 1, so that the light incident on the window member 6 (incident light flux) is the core. The light that is larger (more) than the light incident on the end face of 1 and that is incident from the increased area of the end face of the window member 6 is reflected by the outer peripheral surface of the window member 6 and therefore does not leak light. The light enters the end surface of the core 1. Therefore, a larger amount of incident light can be obtained than that directly incident from the end face of the core 1 as shown in FIG. In addition, since the configuration is simpler than that shown in FIGS. Further, since the window member 6 is fastened by the ring spring 26, the end portion of the core 1 can be prevented from being deformed, and light leakage due to the deformation of the core 1 can be eliminated so that the light guide efficiency is not lowered. Is. Furthermore, when the window material 6 is formed of glass, infrared rays can be absorbed by the window material 6, and the temperature rise of the end face of the core 1 can be suppressed.
[0064]
  Figure 9 shows anotherReference exampleIndicates. thisReference exampleIn FIG. 8, instead of the silica airgel 41, a sheet 55 having a multilayer mirror surface (a surface having a high regular reflectance) is formed, and the mirror surface is brought into close contact with the outer peripheral surface of the window member 6. 55 is covered over the entire circumference. Further, instead of the airgel 41, a member whose inner surface is formed into a mirror surface by aluminum vapor deposition or silver vapor deposition may be disposed in close contact. Further, an aluminum vapor deposition film or a silver vapor deposition film may be formed on the outer peripheral surface of the window member 6.
[0065]
  thisReference exampleIn order to make the outer diameter of the window material 6 larger than the outer diameter of the core 1 so that the cross-sectional area of the window material 6 is larger than the cross-sectional area of the core 1 and to cover the outer peripheral surface of the window material 6 with the mirror sheet 55. In addition, when light enters from an area increasing portion of the end face of the window member 6 outside the end face of the core 1, the light incident on the window member 6 (incident light beam) is larger than the light incident on the end face of the core 1. Most of the light incident from the increased area of the end surface of the window member 6 is reflected on the outer peripheral surface of the window member 6 and is incident on the end surface of the core 1 without leaking light. Become. Therefore, a larger amount of incident light can be obtained than that directly incident from the end face of the core 1 as shown in FIG.
[0066]
  The other in FIG.Reference exampleIndicates. A cover 10 is provided instead of the cap 4 of the optical fiber A shown in FIG.Reference exampleThe core 1 and the tube 2 are the same as described above. The cover 10 has an annular holding portion 21, a window member 6 formed on the inner side of the holding portion 21, and a substantially cylindrical shape that protrudes to the back side of the window member 6 and is integrally formed on the outer periphery of the holding portion 21. It is comprised with the fitting part 9. FIG. The window material 6 is formed of a transparent and hard acrylic resin having a refractive index equivalent to that of the core 1 or a transparent glass or resin close to the refractive index of the core, and is formed so as not to be easily deformed even when an external force is applied. . The plate-like window material 6 can be fitted and held inside the holding portion 21 to form the cover 10. The diameter of the window material 6 is larger than the outer diameter of the core 1 and smaller than the inner diameter of the tube 2. The fitting portion 9 is made of metal so that it can be caulked and deformed. The inner peripheral shape of the fitting portion 9 is formed substantially equal to the outer peripheral shape of the tube 2, and the inner diameter of the fitting portion 9 is formed substantially the same as the outer diameter of the tube 2. Furthermore, the holding part 21, the fitting part 9, and the center of the window material 6 are formed so as to substantially coincide with each other.
[0067]
When attaching the cover 10 to the end portion of the tube 2, the end portion of the tube 2 is inserted inside the fitting portion 9 so that the outer periphery of the end portion of the tube 2 is in contact with the inner peripheral surface of the fitting portion 9. Thereafter, a part of the fitting part 9 is caulked and deformed inward over the entire circumference to form a protruding part 28 that protrudes inward, and a part of the end of the tube 2 is formed by the protruding part 28. The protrusion 29 is deformed inward over the entire circumference, and the protrusion 29 is pressed against the entire circumference of the outer peripheral surface of the core 1. Further, the center of the window material 6 and the center of the end surface of the core 1 are substantially matched, and in this state, the surface of the window material 6 on the core 1 side is brought into close contact with the end surface of the core 1 and the surface of the window material 6 on the core 1 side and the core. The end face of 1 is bonded with an acrylic or glass-based transparent adhesive 8.
[0068]
By attaching the cover 10 to the end portion of the tube 2 in this way, the end portion of the core 1 and the end portion of the tube 2 are in a state in which the center of the window material 6 and the center of the end surface of the core 1 are substantially matched. The center of the core 1 is fixed near the center of the optical fiber A, and the center of the core 1 is fixed near the center of the tube 2. That is, the centers of the core 1, the tube 2, and the air layer 3 are substantially matched so that the core 1 and the tube 2 are disposed concentrically, and this state is maintained by the cover 10. In addition, the centers of the core 1, the tube 2, the air layer 3, the window material 6, the holding part 21, and the fitting part 9 are arranged so as to substantially coincide with each other. In addition, the inside of the tube 2 is substantially sealed (a state where the seal is fixed) by the caulking and fixing cover 10. Accordingly, the cover 10 is provided instead of the cap 4 of the optical fiber A shown in FIG. 1, and the same effect as the optical fiber A shown in FIG. 1 is obtained. Further, the structure is simpler and less expensive than the embodiment of FIG.
[0069]
  The other in FIG.Reference exampleIndicates. In the embodiment shown in FIG. 10, the tube 2 and the cover 10 are fixed by an adhesive 8 instead of fixing by caulking. That is, the outer peripheral surface of the end portion of the tube 2 and the inner peripheral surface of the fitting portion 9 are bonded and fixed with the adhesive 8, and the inside of the tube 2 is sealed with the cover 10. Other configurations are shown in FIG.Reference exampleIt is the same.
[0070]
  thisReference exampleThen, compared with the thing of FIG. 10, since the contact area of the outer peripheral surface of the edge part of the tube 2 and the inner peripheral surface of the fitting part 9 becomes large, airtightness improves. Further, since the fixing is not performed by caulking, the core 1 is not deformed, and the light guide efficiency can be prevented from being lowered. Furthermore, since there is no contact between the tube 2 and the core 1, the light guide efficiency is improved.
[0071]
  The other in FIG.Reference exampleIndicates. thisReference exampleIn FIG. 10, the tube 2 and the cover 10 are fixed by the adhesive tape 40 instead of fixing by caulking. That is, the adhesive tape 40 is attached so as to cover the outer peripheral surface of the end portion of the tube 2 and the outer peripheral surface of the fitting portion 9, and the inside of the tube 2 is sealed with the cover 10. Other configurations are shown in FIG.Reference exampleIt is the same. thisReference exampleHas the same effect as the embodiment of FIG.
[0072]
【The invention's effect】
  As described above, according to the first aspect of the present invention, a transparent core having a circular or elliptical cross section and having a flexible inner diameter is larger than an outer diameter of the core and is in a flexible tube. In an optical fiber disposed and an air layer interposed between the outer periphery of the core and the inner periphery of the tube,The cap is formed of a hard transparent material having the same refractive index as the core,An insertion part formed in a cylindrical shape having the same shape as the outer diameter of the core provided with caps at both ends of the tube so that the center of the core is fixed near the center of the tube and the inside of the tube is substantially sealed. Since the insertion part is inserted into the gap between the core and the tube and the outer periphery of the tube outside the insertion part is fastened and fixed, the core can be firmly fixed to the tube and the cap and The optical axis can be easily and stably positioned by positioning and fixing the cap and tube with respect to the optical axis of the reflection system such as the light source and the reflecting plate. It is possible to prevent a decrease in light collection efficiency. In addition, dust intrusion into the tube, dust adhering to the core, moisture intrusion into the tube, and condensation can be prevented, and scattering due to dust or moisture on the surface of the core can occur. Thus, the light guide property can be prevented from being impaired. Furthermore, it is possible to prevent deformation by fixing the end of the core with a cap, so that light leakage due to deformation of the core is eliminated and the light guide efficiency is not lowered.In addition, at least at the interface between the outer surface of the insertion portion and the inner surface of the tube, there is a member having at least a lower refractive material than the tube or a mirror surface on the inner surface, thus preventing light leakage at the interface between the outer surface of the insertion portion and the inner surface of the tube. It is possible to improve the light guide efficiency.
[0074]
  The invention of claim 2 of the present invention is such that the outer diameter of the insertion portion is the inner diameter of the tube.Smaller thanTherefore, the adhesion between the insertion portion and the tube can be increased, and the degree of sealing in the tube can be further increased.
[0075]
  Claims of the invention3In this invention, since the end of the cap facing the insertion portion is a transparent window material, light can be reliably incident on the end of the core through the window material.
[0078]
  Claims of the invention4In this invention, since the surface of the cap that contacts the outer peripheral surface of the core is a mirror surface, light leakage at the contact portion between the outer periphery of the core and the surface of the cap can be prevented, and light guide efficiency can be improved. Is.
[Brief description of the drawings]
FIG. 1 of the present inventionReference exampleFIG.
[Figure 2] Other aboveReference example(A) and (b) are some sectional drawings.
[Figure 3] Same as aboveReference example(A) and (b) are some sectional drawings.
[Figure 4] Same as aboveReference example(A) (b) (c) (d) is a partial cross-sectional view.
[Figure 5]Of the present inventionAn example of an embodiment is shown and (a) and (b) are some sectional views.
FIGS. 6A and 6B show an example of another embodiment, and FIGS. 6A and 6B are partial cross-sectional views. FIGS.
FIG. 7 is a partial cross-sectional view showing a reference example of the same.
FIG. 8 is a partial cross-sectional view showing another reference example.
FIG. 9 is a partial cross-sectional view showing another reference example.
FIGS. 10A and 10B show another reference example, and FIGS. 10A and 10B are partial cross-sectional views. FIGS.
FIGS. 11A and 11B show another reference example, and FIGS. 11A and 11B are partial cross-sectional views. FIGS.
FIGS. 12A and 12B show another reference example, and FIGS. 12A and 12B are partial cross-sectional views. FIGS.
13A is a cross-sectional view showing a conventional example, and FIG. 13B is a schematic view of an optical fiber system for illumination.
14A is a cross-sectional view showing a conventional example, and FIG. 14B is a cross-sectional view showing problems of the conventional example.
[Explanation of symbols]
  1 core
  2 tubes
  3 Air layer
  4 Cap
  5 Insertion part
  6 Window material
  8 Adhesive
  9 Fitting part
  10 Cover
  A Optical fiber

Claims (4)

A transparent core having a circular or elliptical cross section and having flexibility is disposed in a flexible tube having an inner diameter larger than the outer diameter of the core and having flexibility, and the outer periphery of the core and the inner periphery of the tube. In an optical fiber with an air layer in between , a cap is formed of a hard transparent material having a refractive index comparable to that of the core, the center of the core is fixed near the center of the tube, and the inside of the tube is substantially sealed Caps are provided at both ends of the tube, an insertion portion formed in a cylindrical shape substantially the same shape as the outer diameter of the core is provided in the cap, the insertion portion is inserted into the gap between the core and the tube, and the insertion portion the outer fixed by tightening the outer circumference of the tube, the interface between the outer surface and the inner surface of the tube of the insertion portion, an optical fiber having a low refractive material, or the inner surface of at least the tube is characterized by comprising a member which is a mirror The optical fiber according to claim 1, wherein an outer diameter of the insertion portion is smaller than an inner diameter of the tube.   The optical fiber according to claim 1 or 2, wherein an end portion of the cap facing the insertion portion is a transparent window material. The optical fiber according to any one of claims 1 to 3, wherein the surface of the cap that contacts the outer periphery of the core is a mirror surface .

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