JP2012093520A - Optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber having so-called low loss and high relative index difference and an optical fiber bundle capable of efficiently combining light of an illumination light source, light of a high power light source, light of a resin curing UV light source and the like, transmitting them with low loss to irradiate a wide field of view with the combined light.SOLUTION: An inventive optical fiber 10 consists of a hollow glass tube 4 and an optical fiber body 50 arranged in the hollow glass tube 4 and having a glass core 1 that has a circular cross-section through which light propagates and a glass thin layer 2 covering the outer periphery of the glass core 1. The hollow glass tube 4 has a through-hole 5 that has a square a cross section, and the optical fiber body 50 is arranged in the through-hole 5 of the hollow glass tube 4 such that four contact parts 61 to 64 of the optical fiber body 50 are brought into contact with the inner peripheral surface of the hollow glass tube 4. Because of this constitution, four gap parts extending in the longitudinal direction are formed between the optical fiber body 50 and the hollow glass tube 4, except the contact parts 61 to 64.

Description

  The present invention provides light for illumination light source, light for high power light source (exposure, light sterilization, fluorescence observation, photocatalyst, spectral light source, gas analysis, liquid crystal sealing, light for light source such as LED for plant growth), resin curing The present invention relates to an optical fiber that can efficiently combine light of a UV light source, light of an ink curing light source, light of a dental resin curing light source, etc., propagate with low loss, and irradiate a wide field of view.

  With the development and spread of optical fiber communication, many optical technologies such as optical components, optical devices, and optical transmission systems have come to be applied in various fields other than optical fiber communication. For example, optical fibers that transmit light from an illumination light source, high-power light, UV light for resin curing, signal transmission light, excimer laser light, and the like, and optical fiber bundles in which optical fibers are bundled have been put into practical use.

  The characteristics of the optical fiber required for these applications are that the light is efficiently coupled to the incident end of the optical fiber, and the light is propagated from the incident end to the outgoing end of the optical fiber without being attenuated as much as possible. To emit light brightly. In response to such demands, it has been proposed to use quartz glass materials, multicomponent glass materials, and plastic materials as optical fiber materials.

Among them, as an optical fiber that emits illumination light as brightly as possible from the emission end of the optical fiber, an optical fiber 20 made of a silica-based glass material as shown in FIG. 12 has been commercialized. The optical fiber 20 is used SiO ₂ glass core 21 in order to reduce the attenuation of light, it is constructed using the SiO ₂ glass doped with F (fluorine) in the cladding 22 of the outer periphery thereof. As shown in FIG. 13, an optical fiber bundle 201 in which a plurality of optical fibers 20 are bundled to form a bundle structure is commercialized. The said optical fiber is disclosed by patent documents 1-3.

Japanese Patent Laid-Open No. 2003-121662 JP 2003-161849 A Japanese Patent Laid-Open No. 2004-354660

However, the following problems exist in optical fibers made of a silica glass material for propagating light from an illumination light source, light from a high-power light source, light from a UV light source for resin curing, and the like.
(1) Since the relative refractive index difference Δ << Δ = [(nw-nc) / nw] × 100% >> between the refractive index nw of the core and the refractive index nc of the cladding is as small as about 0.2%, the opening angle Becomes as small as about 23 °, and the light from the light source cannot be efficiently coupled and propagated in the optical fiber.
(2) Since the relative refractive index difference is small, the spread of light emitted from the exit end is narrow, and it is difficult to irradiate the exit side over a wide range.
(3) When the optical fiber is bent, the light in the core leaks into the clad, and the optical power in the optical fiber fluctuates or the loss due to bending of the optical fiber increases.
(4) Since the core and the clad of the optical fiber are made of a brittle material made of glass, the mechanical bending strength is weak and it is difficult to bend freely with a small radius of curvature.

  The present invention has been made to solve the above-described conventional problems, and its purpose is to efficiently combine light from a light source for illumination, light from a high power light source, light from a UV light source for resin curing, and the like. It is an object of the present invention to provide a so-called low-loss optical fiber and optical fiber bundle that can be transmitted with low loss and irradiate a wide field of view.

The present invention
A hollow glass tube,
An optical fiber body having a circular glass core with a circular cross section disposed inside the hollow glass tube;
An optical fiber comprising:
The optical fiber body is in contact with the inner peripheral surface of the hollow glass tube with at least two contact portions, and a gap extending in the longitudinal direction is formed between the optical fiber body other than the contact portion and the hollow glass tube. It is characterized by that.
In this case, one optical fiber body may be disposed inside the hollow glass tube, or a plurality of optical fiber bodies may be disposed.

  In the optical fiber, the hollow glass tube has a through-hole having a rectangular or triangular cross section inside or a through-hole having an elliptical cross section inside, and the optical fiber main body is in the through hole. It is preferable that they are arranged.

  Moreover, it is the structure which the external shape of the cross section of the said hollow glass tube may be circular shape or square shape.

Further, the hollow glass tube may have a plurality of through holes therein, and the optical fiber body may be disposed in each through hole. In this case, one optical fiber main body may be disposed in the through hole, or a plurality of optical fiber main bodies may be disposed.
In the optical fiber, the glass core can be made of SiO ₂ glass.

In the optical fiber, the optical fiber main body has a thin layer made of glass having a refractive index lower than that of the glass core formed on the outer periphery of the glass core, and the thin layer is formed of the hollow glass tube. It is preferable to configure so as to be in contact with the inner peripheral surface.
The thin layer is preferably composed of SiO ₂ glass to which F or B ₂ O ₃ is added.

Said hollow glass tube, SiO ₂ or glass, may consist of SiO ₂ glass doped with F or B ₂ O _3.
The hollow glass tube is preferably covered with a reinforcing member.

  The optical fiber bundle of the present invention is characterized in that a plurality of the optical fibers described above are bundled to form a bundle.

The present invention has the following effects.
First, in the optical fiber according to the present invention, an optical fiber main body having a glass core having a circular cross section is arranged inside the hollow glass tube so as to be in contact with the inner peripheral surface of the hollow glass tube with at least two contact portions. The gap between the hollow glass tube and the optical fiber main body other than the contact portion is a gap extending in the longitudinal direction. Therefore, most of the outer periphery of the glass core through which light propagates becomes a void (cladding layer). For example, when the glass core is formed from SiO ₂ glass and the void is an air layer, the glass core and the void The relative refractive index difference with the part is about 30%. This value is about an order of magnitude larger than that of a conventional optical fiber.

  Further, in an optical fiber according to another aspect of the present invention, an optical fiber body is composed of a glass core having a circular cross section and a thin layer made of glass having a refractive index lower than that of the glass core formed on the outer periphery thereof. The optical fiber main body was disposed inside the hollow glass tube so as to be in contact with the inner peripheral surface of the hollow glass tube with at least two contact portions. Between the hollow glass tube other than the contact portion and the optical fiber main body, a gap portion extending in the longitudinal direction was formed. For this reason, the glass core through which light propagates is surrounded by a thin layer (first cladding layer) having a low refractive index, and most of the outer periphery of the thin layer becomes a void (second cladding layer).

In the optical fiber according to another embodiment, since the glass core is in direct contact is thin layer, for example, a glass core formed of SiO ₂ glass, was formed of SiO ₂ glass a thin layer F is added In this case, the relative refractive index difference between the glass core and the thin layer is the same as that of the conventional optical fiber. However, as described above, the clad layer is composed of a thin layer and a gap, and the gap occupies most of the clad layer (that is, the gap is the dominant structure of the clad layer). The relative refractive index difference between the glass core and the clad layer can be obtained approximately from the refractive index of SiO ₂ glass and the refractive index of the void (air layer). For this reason, even in another optical fiber, the relative refractive index difference between the glass core and the clad layer is about 30%, which is about one digit larger than that of the conventional optical fiber.

  As described above, since the optical fiber of the present invention has a large relative refractive index difference between the glass core and the cladding layer, the opening angle of the optical fiber becomes a value close to 180 °. It is possible to propagate the light in the optical fiber by combining the light of the UV light, the light of the UV light source for resin curing, etc. very efficiently. Moreover, since light can be emitted with a wide spread from the emission end, the emission end side of the optical fiber can be illuminated widely.

  Note that the contact portion between the inner peripheral surface of the hollow glass tube and the optical fiber body is close to a line contact, and thus is negligibly small as compared with the gap portion.

  The optical fiber of the present invention is resistant to mechanical bending since at least two voids are provided in the optical fiber. Also, since it has a large relative refractive index difference, leakage of light propagating in the optical fiber to the cladding layer and fluctuation of the light intensity in the glass core when bent are overwhelming compared to conventional optical fibers. Very few. Further, in the conventional optical fiber, stress is generated due to temperature fluctuation due to the difference in thermal expansion coefficient between the glass core and the clad layer, and the optical power fluctuation in the optical fiber occurs depending on this stress. In the optical fiber, the stress can be relieved in the gap between the optical fiber body and the hollow glass tube. For this reason, it becomes possible to reduce the optical power fluctuation | variation in an optical fiber.

  When the cross-section of the through hole inside the hollow glass tube is a quadrangular shape or a triangular shape, the optical fiber main body is in line contact with the inner peripheral surface of the hollow glass tube at a plurality of points (2 to 4 points), and most of the gaps are The hollow glass tube is disposed in a state surrounded by a second cladding layer. For this reason, the relative refractive index difference between the glass core and the cladding layer becomes extremely large, and the opening angle of the optical fiber can be set to a value close to 180 °. Therefore, the light from the illumination light source, the light from the high power light source, the light from the resin curing UV light source, and the like can be further efficiently combined and propagated in the optical fiber. In addition, since the gap is increased, the mechanical strength against bending can be further increased, and leakage of light loss and fluctuation of light intensity due to bending can be further reduced.

  If the outer shape of the cross section of the hollow glass tube is circular or quadrangular, the optical fiber has a symmetrical shape, so that it can be easily manufactured and handled. Further, the mechanical strength against bending is increased. Further, even if the optical fiber is bent in an arbitrary direction, leakage of light propagating in the glass core to the cladding layer and fluctuation of light intensity in the glass core can be reduced.

  A hollow glass tube is provided with a plurality of through-holes, and an optical fiber body is arranged inside each through-hole, so that the light of the illumination light source, the light of the high power light source, the UV light source for resin curing A large amount of light or the like can be confined in a plurality of glass cores and propagated in the optical fiber. That is, high intensity optical power can be propagated.

  Further, by bundling a plurality of the above-mentioned optical fibers into a bundle shape to form an optical fiber bundle, it is possible to couple the optical power with higher intensity into the optical fiber bundle and propagate the light.

In the present invention, when the glass core is made of SiO ₂ glass, the light of the light source in the near-infrared wavelength band can be propagated with low loss from the light of the light source in the ultraviolet wavelength band having a shorter wavelength. Thereby, the optical fiber or optical fiber bundle of the present invention can be used in various applications such as ultraviolet transmission, illumination, resin curing UV transmission, fluorescence analysis, medical laser knife, excimer laser guide, spectroscopic analysis guide, Can be applied to signal transmission, soft laser guide, high power light guide, plant growth LED light transmission, semiconductor exposure device, photo sterilization, photocatalyst, liquid crystal sealing, gas analysis, etc. It becomes possible.

  In addition, if the cross section of the through-hole inside the hollow glass tube is elliptical, the gap provided between the optical fiber body other than the contact portion and the hollow glass tube can be widened, so that more mechanical bending can be achieved. A strong optical fiber can be realized.

The glass core is formed of SiO ₂ glass, by forming the SiO ₂ glass a thin layer was added F or B ₂ O _3, making the refractive index of the thin layer about 0.2% lower than the refractive index of the glass core Can do. Thereby, light can be confined in the glass core, and the confinement of light to the glass core can be further strengthened in the gap provided between the glass core other than the contact part and the hollow glass tube.

Furthermore, to form the glass core of SiO ₂ glass, formed of SiO ₂ glass a thin layer was added F or B ₂ O _3, and the hollow glass tube was added SiO ₂ glass, or F or B ₂ O ₃ When formed from SiO ₂ glass, all materials of the optical fiber can be made of SiO ₂ glass. Therefore, in manufacturing the optical fiber, it is possible to reduce the deformation of the structure due to mismatching of the softening temperature and the thermal expansion coefficient, the generation of stress, and the like.

  When the outer periphery of the hollow glass tube is covered with a reinforcing member, the strength against mechanical bending of the optical fiber can be further improved.

The optical fiber which concerns on 1st Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The optical fiber which concerns on 2nd Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The optical fiber which concerns on 3rd Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The optical fiber which concerns on 4th Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The optical fiber which concerns on 5th Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The optical fiber which concerns on 6th Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The cross-sectional view of the optical fiber which concerns on 7th Example of this invention. The cross-sectional view of the optical fiber which concerns on 8th Example of this invention. The cross-sectional view of the optical fiber bundle which concerns on 9th Example of this invention. The cross-sectional view of the optical fiber bundle which concerns on 10th Example of this invention. The optical fiber which concerns on 11th Example of this invention is shown, (a) is a cross-sectional view, (b) is an external view. The conventional optical fiber is shown, (a) is a cross-sectional view, (b) is an external view. The optical fiber bundle comprised by bundling the conventional optical fiber is shown, (a) is a cross-sectional view, (b) is an external view.

  Hereinafter, specific examples of the present invention will be described.

  FIG. 1 shows a first embodiment of an optical fiber according to the present invention. FIG. 4A is a cross-sectional view, and FIG. The optical fiber 10 includes a hollow glass tube 4 having a through-hole 5 having a square cross section and an optical fiber body 50 disposed in the through-hole 5. The optical fiber body 50 has a structure in which the outer periphery of a glass core 1 having a circular cross section is protected by a glass thin layer 2 (first cladding layer) having a lower refractive index than the glass core 1. The outer periphery of the thin layer 2 is in contact with the inner peripheral surface of the hollow glass tube 4 at four contact portions (61, 62, 63, 64). The contact portions 61 to 64 extend linearly from one end portion to the other end portion of the hollow glass tube 4. With such a configuration, the outer periphery of the optical fiber body 50 is in line contact with the inner peripheral surface of the hollow glass tube 4. Except for the contact parts 61-64 which do, it has the structure covered with the space | gap part 3 (2nd clad layer).

The hollow glass tube 4 has a circular outer shape in cross section. Further, using the SiO ₂ glass to the glass core 1 in this embodiment, SiO ₂ is used glass doped with F in the glass thin layer 2. The hollow glass tube 4 was made of SiO ₂ glass.

It is the low refractive index glass thin layer 2 formed on the outer periphery of the glass core 1 and the gap 3 that act as a cladding layer surrounding the glass core 1. Since most of the clad layer of the optical fiber 10 according to the present embodiment is occupied by the gap 3 (that is, the air layer) that is the second clad layer, the gap between the glass core 1 made of SiO ₂ glass and the clad layer is occupied. The relative refractive index difference Δ is about 30%, which is about one digit larger than the relative refractive index difference Δ of the conventional optical fiber. Therefore, the opening angle of the optical fiber becomes a value close to 180 °, and the light incident from one incident end of the optical fiber can be coupled very efficiently and strongly confined and propagated in the glass core 1.

  Further, the optical fiber 10 of this embodiment is resistant to mechanical bending. Further, even if the optical fiber 10 of the present embodiment is bent, leakage of light propagating in the optical fiber 10 to the cladding layer and fluctuation of the light intensity in the glass core 1 are overwhelming as compared with the conventional optical fiber. Few.

  In the conventional optical fiber, due to the difference in thermal expansion coefficient between the glass core 1 and the clad layer, stress is generated due to temperature fluctuation, and optical power fluctuation in the optical fiber depends on this stress. In the optical fiber 10, since the stress can be relieved by the gap 3 between the glass core 1 and the hollow glass tube 4, fluctuations in optical power in the optical fiber 10 can be reduced.

Using SiO ₂ glass to the glass core 1 in this embodiment, a SiO ₂ glass doped with F in the glass thin layer 2. Since the hollow glass tube 4 is made of SiO ₂ glass, it becomes a multimode optical fiber having a very large relative refractive index difference Δ. The diameter of the glass core 1 is preferably in the range of 10 μm to 150 μm, but up to about 200 μm is an acceptable range. Since the glass thin layer 2 has a thickness of 2 μm to 20 μm, it is sufficient to optically protect the glass core 1. The diameter of the hollow glass tube 4 is preferably in the range of 100 μm to 300 μm because it can withstand practical bending. However, even if it is larger than that, it can be used because it is easy to bend because its outer periphery is covered with a polymer material in actual use. For the glass thin layer 2, SiO ₂ glass added with B ₂ O ₃ may be used. The cross section of the through hole 5 in the hollow glass tube 4 may be rectangular instead of square. In this case, the glass core 1 is disposed so as to be in contact with the rectangular space at two points.

As a method of processing the cross section of the through hole 5 in the hollow glass tube 4 into a square shape, a method of grinding the center portion of the SiO ₂ glass rod can be used. In addition, as a method other than that, by using a sol-gel method, a glass raw material liquid is poured into a metal mold having a square inner cross section and a circular outer shape, and is taken out of the mold after drying and heat-treated. Can be used.

The reason why SiO ₂ glass is used for the glass core 1 is to realize an optical fiber that can be propagated with low loss from the ultraviolet region to the near infrared region. In addition to the above SiO ₂ glass, additives for refractive index control SiO ₂ or glass containing (GeO _2, etc. _{P 2 O 5, TiO 2,} N), or the like may be used glass multicomponent.

The hollow glass tube 4 is preferably close to the material of the glass core 1 in order to reduce the mismatch between the thermal expansion coefficient and the softening temperature. For example, SiO ₂ glass to which F or B is added in addition to SiO ₂ glass can be used. The may be formed of SiO ₂ glass layer obtained by adding F and B on the inner surface of the SiO ₂ glass. Further, SiO ₂ glass containing an additive for controlling the refractive index (B ₂ O ₃ , GeO ₂ , P ₂ O ₅ , TiO _2, etc.) or multicomponent glass may be used.

A specific method for manufacturing the optical fiber 10 will be described. First, grinding was performed so that a through-hole having a square cross section was formed at the center of the SiO ₂ glass rod, and further grinding was performed so that the outer cross section of the SiO ₂ glass rod was circular. Next, a new SiO ₂ glass rod was prepared and ground so that the outer cross section was circular, and a SiO ₂ glass layer to which F was added was formed on the outer periphery using a gas phase chemical reaction. Then, the SiO ₂ glass rod covered with the SiO ₂ glass layer to which F was added was inserted into the through hole in the SiO ₂ glass rod in which the through hole was formed to produce an optical fiber preform. While inserting this optical fiber preform into a high-temperature (about 2000 ° C.) drawing electric furnace of an optical fiber drawing apparatus at a constant speed, the optical fiber 10 is stretched and wound around a winding drum at a desired speed. Was made.

Next, a prototype example of the optical fiber 10 of this embodiment will be described. An optical fiber having a glass core 1 made of SiO ₂ glass having a diameter of 50 μm, a thin SiO ₂ glass layer 2 (refractive index of 1.442) added with F of 10 μm, and a hollow glass tube 4 made of SiO ₂ glass having a diameter of 150 μm. Prototype. An optical loss was measured by coupling an excimer laser beam having a wavelength of 248 nm into the optical fiber 10 with a high coupling efficiency close to 80% (a coupling efficiency of about 50% with a conventional optical fiber). As a result, the optical loss was 72 dB / km, which was a low loss characteristic. Moreover, the result of measuring the loss using a semiconductor laser beam having a wavelength of 1.3 μm was 0.8 dB / km.

  It was found that the allowable bending radius of the optical fiber 10 of the prototype was about 10 mm. This value was about half that of a conventional optical fiber.

In the above embodiment, an SiO ₂ glass layer to which F is added may be formed on the inner surface of the through hole 5 in the hollow glass tube 4.

  FIG. 2 shows a second embodiment of the optical fiber of the present invention. FIG. 4A is a cross-sectional view, and FIG. The optical fiber 10 has substantially the same configuration as that of the embodiment of FIG. 1 except that a through-hole 5 having a rectangular cross section is provided inside a hollow glass tube 4 having a circular outer cross section. The optical fiber body 50 is arranged so as to be in contact with the two contact portions 61 and 63 in the through hole 5.

As in the embodiment of FIG. 1, it is the low refractive index glass thin layer 2 formed on the outer periphery of the glass core 1 that acts as the first cladding layer on the glass core 1, and the gap 3 is This is the second cladding layer. This second clad layer becomes the dominant structure of the clad layer, and light incident from one incident end of the optical fiber 10 is strongly confined in the glass core 1 and propagated. In this embodiment, compared with the embodiment of FIG. 1, the gap 3 has a larger cross-sectional area, and the outer periphery of the low refractive index glass thin layer 2 is not 2 points in the through-hole 5 having the rectangular cross section. Since the contact is made at the points (contact portions 61, 63), the light incident from one incident end of the optical fiber 10 can be more confined and propagated in the glass core 1.
Also in this embodiment, a SiO ₂ glass layer to which F is added may be formed on the inner surface of the through hole 5 in the hollow glass tube 4.

FIG. 3 shows a third embodiment of the optical fiber of the present invention. FIG. 4A is a cross-sectional view, and FIG. This optical fiber 10 has substantially the same configuration as that of the embodiment of FIG. 1 except that the outer shape of the cross section of the hollow glass tube 4 is a square shape. This hollow glass tube 4 was made by grinding a SiO ₂ glass rod so that the outer shape of the cross section became a square shape, and the through hole 5 having a square cross section was ground therein.

In the present embodiment, the outer shape of the cross section of the hollow glass tube 4 may be a structure in which four corners of a square are rounded. This is a hollow glass whose outer cross section is square when an optical fiber preform is inserted into an electric furnace for drawing at a high speed (approximately 2000 ° C) at a constant speed and its tip is drawn into an optical fiber. This is because the four corners of the tube 4 are melt-drawn and rounded.
Further, the outer shape of the cross section of the hollow glass tube 4 is not limited to a square but may be a rectangular shape. Also in this case, a structure in which the four corners of the outer shape of the hollow glass tube 4 are rounded may be used.
An SiO ₂ glass layer to which F is added may be formed on the inner surface of the through hole 5 in the hollow glass tube 4.

  FIG. 4 shows a fourth embodiment of the optical fiber of the present invention. FIG. 4A is a cross-sectional view, and FIG. The optical fiber 10 of this embodiment has substantially the same configuration as that of the third embodiment, but the cross section of the through hole 5 in the hollow glass tube 4 is formed in a rectangular shape, and a low refractive index is formed in the through hole 5. The difference is that the optical fiber body 50 formed by protecting the glass core 1 having a high refractive index in a circular shape with the thin glass layer 2 having the refractive index is disposed so as to be in contact with the two contact portions 61 and 63.

Also in this embodiment, the outer shape of the cross section of the hollow glass tube 4 may be a rectangle other than a square, and may be a structure in which four corners are rounded. An SiO ₂ glass layer to which F is added may be formed on the inner surface of the through hole 5 in the hollow glass tube 4.

FIG. 5 shows a fifth embodiment of the optical fiber of the present invention. FIG. 4A is a cross-sectional view, and FIG. In the optical fiber 10 of this embodiment, the cross section of the through hole 5 in the hollow glass tube 4 having a circular cross section is formed in an elliptical shape, and a low refractive index glass thin film is formed in the elliptical through hole 5. The glass core 1 made of a circular high refractive index protected by the layer 2 is arranged so as to be in contact with the two contact portions 61 and 63. This configuration is also characterized in that the cross-sectional area of the gap 3 can be increased. In order to process the cross section of the through hole 5 in the hollow glass tube 4 into an elliptical shape, it is preferable to perform grinding. An SiO ₂ glass layer to which F is added may be formed on the inner surface of the through hole 5 of the hollow glass tube 4.

FIG. 6 shows a sixth embodiment of the optical fiber of the present invention. FIG. 4A is a cross-sectional view, and FIG. In the optical fiber 10 of this embodiment, the through hole 5 in the hollow glass tube 4 has a triangular cross section (or a substantially triangular shape with three rounded corners), and the optical fiber is formed in the through hole 5. The point which the main body 50 is arrange | positioned so that it may contact | connect in three contact parts (61, 62, 63) differs from 1st Example. Also in this embodiment, a SiO ₂ glass layer to which F is added may be formed on the inner surface of the through hole 5 in the hollow glass tube 4.

FIG. 7 shows a seventh embodiment of the optical fiber of the present invention. This figure shows the schematic of the cross section of the optical fiber 10 which concerns on 7th Example. In the optical fiber 10 according to the seventh embodiment, five through holes 51 to 55 having a square cross section are formed in the glass tube 7, and one optical fiber is formed in each of the through holes 51 to 55. It has the structure which has arrange | positioned the main bodies 501-505. The optical fiber bodies 501 to 505 are composed of a high refractive index glass core 1 having a circular cross section protected by a thin glass layer 2 having a low refractive index.
Thus, since the optical fiber 10 of the present embodiment has five glass cores 1 through which light propagates, it has a function equivalent to that of an optical fiber bundle formed by bundling a plurality of optical fibers.

With SiO ₂ glass of 250μm in diameter glass tube 7 in this embodiment, the glass core 1 for propagating light using a SiO ₂ glass of 50μm in diameter, the glass thin layer 2 (thickness of their periphery 5μm ) Was used SiO ₂ glass (refractive index of 1.443 at a wavelength of 0.633 μm) to which F was added. The through-holes 51 to 55 were formed so that each cross section was a square of 60 μm square.

A method for manufacturing the optical fiber 10 will be described. First, a glass rod made of SiO ₂ glass was prepared, and five through holes 51 to 55 having a square cross section were formed by grinding in the glass rod to produce a hollow glass tube 4. On the other hand, five new glass rods made of SiO ₂ glass were prepared, and after grinding so that the outer diameter of the cross section was circular, F was added to the outer periphery using a gas phase chemical reaction. An SiO ₂ glass layer was formed. A glass rod made of SiO ₂ glass covered with the SiO ₂ glass layer added with these F was inserted into each of the through holes 51 to 55 of the hollow glass tube 4 to prepare an optical fiber preform. Then, the optical fiber preform was stretched while being inserted into a high-temperature (about 2000 ° C.) drawing electric furnace at a constant speed to produce an optical fiber 10. The glass tube 7 may be made of SiO ₂ glass to which F or B is added in addition to SiO ₂ glass.

FIG. 8 shows an eighth embodiment of the optical fiber of the present invention. This figure shows the schematic of the cross section of the optical fiber which concerns on 8th Example. The optical fiber 10 of this embodiment has substantially the same configuration as that of the seventh embodiment, except that nine through holes 51 to 59 are formed in the glass tube 7 as shown in FIG. It is a point. One optical fiber body 501 to 509 is disposed in each of the through holes 51 to 59. Thus, if the number of through holes is large, optical transmission with higher output power can be realized.
The number of the through holes is not limited to 5 or 9, but may be 6 or 7, and may be smaller or larger.

  FIG. 9 shows an optical fiber bundle according to the ninth embodiment of the present invention. This figure shows the schematic of the cross section of the optical fiber bundle 100 which concerns on 9th Example. This optical fiber bundle 100 is a so-called high-density bundle in which seven optical fibers shown in FIG. 1 (indicated by reference numerals 101 to 107 in FIG. 9) are bundled and covered with a covering member 8 made of a polymer material. It has an optical fiber bundle structure. The covering member 8 can be composed of, for example, a silicon resin, a UV curable resin, or the like as a primary covering material, and nylon as a secondary covering material that covers it. Note that the number of optical fibers may be less or more than seven.

  FIG. 10 shows an optical fiber bundle according to the tenth embodiment of the present invention. This figure shows the schematic of the cross section of an optical fiber bundle. The optical fiber bundle 100 according to the tenth embodiment is obtained by coating the outer periphery of the high-density optical fiber bundle according to the ninth embodiment with a reinforcing member 9. The reinforcing member 9 can be made of a polymer material, a metal material, or the like.

  FIG. 11 shows an optical fiber according to an eleventh embodiment of the present invention. FIG. 4A is a cross-sectional view, and FIG. This optical fiber 10 has a structure in which a through-hole 5 having a rectangular cross section is provided in a hollow glass tube 4, and two optical fiber main bodies 50 are arranged in the through-hole 5 with a gap 3 therebetween. is doing. The optical fiber 10 is suitable for irradiating light on a wide lateral area.

In addition, this invention is not limited to the said Example.
It is not necessary to provide a thin layer on the outer periphery of the glass core. In this configuration, the optical fiber main body is composed only of a glass core, and the outer periphery of the glass core is in contact with the inner peripheral surface of the hollow glass tube at two or more contact portions.

The outer periphery of the optical fibers of the first to ninth embodiments and the eleventh embodiment may be coated with a reinforcing member made of a polymer material or a metal material for protecting the optical fiber.
The voids 3 of the optical fibers of the first to eighth embodiments and the eleventh embodiment and the optical fiber bundles of the ninth and tenth embodiments are made to contain an inert gas, and both ends of the optical fiber are sealed. You may make it do.

The refractive index distribution in the glass core 1 may have a flat distribution, a gradient distribution that decreases in the radial direction from the center (for example, a graded refractive index distribution), or a stepped distribution.
In the optical fibers of the seventh and eighth embodiments, the optical fiber body 50 disposed in the through hole of the glass tube 7 may have the structure shown in FIGS. 2 to 6 in addition to the structure shown in FIG.
The second embodiment and the fourth embodiment are examples in which only one optical fiber body 50 composed of the glass core 1 covered with the thin layer 2 is disposed in the through hole 5 in the hollow glass tube 4. A plurality may be arranged side by side through the gap 3 as in the eleventh embodiment. When a plurality of optical fiber main bodies 50 are provided in this way, light can be irradiated to a wide lateral area. The four corners of the cross-section of the through-hole 5 of the first to fourth and seventh to eleventh embodiments need not be right angles, but may be rounded.
Three corners of the triangular through hole 5 in the hollow glass tube 4 of the sixth embodiment may also be rounded.

DESCRIPTION OF SYMBOLS 1 ... Glass core 2 ... Glass thin layer 3 ... Space | gap part 4 ... Hollow glass tube 5, 51-59 ... Through-hole 61-64 ... Contact part 7 ... Glass tube 8 ... Reinforcement member 10, 20 ... Optical fiber 21 ... Core 22 ... Clad 50, 501-509 ... Optical fiber body 100, 101-107, 201 ... Optical fiber bundle

Claims (11)

A hollow glass tube,
An optical fiber body having a circular glass core with a circular cross section disposed inside the hollow glass tube;
An optical fiber comprising:
The optical fiber body is in contact with the inner peripheral surface of the hollow glass tube with at least two contact portions, and a gap extending in the longitudinal direction is formed between the optical fiber body other than the contact portion and the hollow glass tube. An optical fiber characterized by that. The optical fiber according to claim 1, wherein
The hollow glass tube has a through hole having a square or triangular cross section inside, and the optical fiber body is disposed in the through hole. The optical fiber according to claim 1, wherein
The hollow glass tube has a through hole having an elliptical cross section inside, and the optical fiber body is disposed in the through hole. The optical fiber according to any one of claims 1 to 3,
An optical fiber characterized in that an outer shape of a cross section of the hollow glass tube is circular or square. The optical fiber according to any one of claims 1 to 4,
The hollow glass tube has a plurality of through holes therein, and the optical fiber main body is disposed in each of the through holes. In the optical fiber according to any one of claims 1 to claim 5, wherein the glass core optical fiber, characterized in that it consists of SiO ₂ glass. The optical fiber according to any one of claims 1 to 6,
The optical fiber body has a thin layer made of glass having a refractive index lower than that of the glass core formed on the outer periphery of the glass core, and the thin layer is in contact with the inner peripheral surface of the hollow glass tube. And optical fiber. In the optical fiber according to claim 7, wherein the thin layer is an optical fiber which is characterized in that it consists of SiO ₂ glass doped with F or B ₂ O _3. In the optical fiber according to any one of claims 1 to claim 8, wherein the hollow glass tube is SiO ₂ or glass, optical fiber, characterized in that it consists of SiO ₂ glass doped with F or B ₂ O _3.   The optical fiber according to any one of claims 1 to 9, wherein the hollow glass tube is covered with a reinforcing member.   An optical fiber bundle comprising a bundle of a plurality of optical fibers according to any one of claims 1 to 10.

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