Optical fiber bundle and optical fiber bundle device

Abstract

To provide an optical fiber bundle and an optical fiber bundle device which can increase the amount of an outgoing beam.SOLUTION: In an optical fiber bundle 2 formed by bundling a plurality of optical fibers, an end part 21 at least on one side of the optical fiber bundle 2 in an axial direction is a taper part 23 formed into a tapered shape. In the end part 21 at least on the one side of the optical fiber bundle 2 in the axial direction, a portion at least on the side of an end surface 23t of the taper part 23 is a heat seal part 26 formed by heat-sealing the plurality of optical fibers. The plurality of optical fibers respectively have a numerical aperture NA of 0.4 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber bundle and an optical fiber bundle device. [Background technology]

[0002] As a conventional optical fiber bundle, there is an optical fiber bundle in which optical fibers are converged into a tapered shape by thermal fusion at the end (for example, Patent Document 1). According to Patent Document 1, the thermal fusion improves heat resistance compared to when the optical fibers are fixed with an adhesive, and the tapered shape increases the irradiation density. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-047426 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional optical fiber bundle, there is still room for improvement in the amount of light emitted from the emission end face (hereinafter, referred to as "emitted light amount").

[0005] An object of the present invention is to provide an optical fiber bundle and an optical fiber bundle device capable of improving the amount of emitted light. [Means for solving the problem]

[0006] The optical fiber bundle of the present invention comprises: An optical fiber bundle comprising a plurality of optical fibers, At least one end of the optical fiber bundle in the axial direction is a tapered portion having a tapered shape, At least an end surface side portion of the tapered portion at least on one side of the end portion in the axial direction of the optical fiber bundle is a heat fused portion in which the optical fibers are heat fused to each other, Each of the optical fibers has a numerical aperture NA of 0.4 or more.

[0007] In the optical fiber bundle of the present invention, It is preferable that the end portion on one side in the axial direction of the optical fiber bundle is an input end portion.

[0008] In the optical fiber bundle of the present invention, It is preferable that each of the plurality of optical fibers has a numerical aperture NA of 0.5 or more.

[0009] In the optical fiber bundle of the present invention, It is preferable that each of the plurality of optical fibers has a numerical aperture NA of 0.7 or more.

[0010] In the optical fiber bundle of the present invention, It is preferable that a part of the light incident on the end face of the tapered portion is confined in the core after entering the cladding inside the thermal fusion portion.

[0011] In the optical fiber bundle of the present invention, It is preferable that, in a cross section taken along the central axis of the optical fiber bundle, the outer peripheral surface of the tapered portion extends linearly toward the central axis as it approaches the end face of the tapered portion.

[0012] In the optical fiber bundle of the present invention, It is preferable that, inside the heat-sealed portion, the diameter of each core gradually decreases toward the end face of the tapered portion.

[0013] The optical fiber bundle device of the present invention comprises: The optical fiber bundle described above; A light source; Equipped with The optical fiber bundle is configured so that light from the light source is incident on an end face of the end on one side in the axial direction. Effect of the Invention

[0014] According to the present invention, it is possible to provide an optical fiber bundle and an optical fiber bundle device capable of improving the amount of emitted light. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing an optical fiber bundle device according to one embodiment of the present invention; [Diagram 2] 2 is a diagram for explaining the configuration of the optical fiber bundle of FIG. 1. [Diagram 3] 2 is a diagram for explaining the operation of the optical fiber bundle of FIG. 1. [Figure 4] 2 is a diagram for explaining an example of a method for forming a tapered portion of the optical fiber bundle of FIG. 1. [Diagram 5] 2 is a schematic diagram showing an example of a configuration in which the optical fiber bundle device of FIG. 1 is configured as an endoscope. FIG. [Figure 6] 1 is a graph showing experimental results of an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The optical fiber bundle and optical fiber bundle device of the present invention can be used in any device equipped with an optical fiber bundle and a light source, but is particularly suitable for use in, for example, lighting fixtures or industrial or medical endoscopes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an optical fiber bundle and an optical fiber bundle device according to the present invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals.

[0017] FIG. 1 is a schematic diagram of an optical fiber bundle device 1 according to an embodiment of the present invention. The optical fiber bundle device 1 includes an optical fiber bundle 2 and one or more (one in the example of FIG. 1) light sources 3. The optical fiber bundle device 1 can be configured as any device including an optical fiber bundle and a light source, but can be particularly preferably configured as, for example, a lighting device or an industrial or medical endoscope (FIG. 5). When the optical fiber bundle device 1 is configured as a lighting device or an industrial or medical endoscope, it is preferable that the optical fiber bundle 2 is configured as a light guide.

[0018] Fig. 2 is a diagram for explaining the configuration of the optical fiber bundle 2 in Fig. 1. The optical fiber bundle 2 is formed by bundling a plurality of optical fibers 25 (Fig. 2). As shown in Figs. 1 and 2, at least an end portion 21 on one axial side of the optical fiber bundle 2 is a tapered portion 23 having a tapered shape. In the example of Fig. 1, only the end portion 21 on one axial side of the optical fiber bundle 2 is the tapered portion 23. However, the end portions 21, 22 on both axial sides of the optical fiber bundle 2 may be tapered portions 23. In this specification, the term “axial direction” refers to a direction parallel to the central axis (optical axis) O of the optical fiber bundle 2 . An end 21 on one axial side of the optical fiber bundle 2 is an input end. An end 22 on the other axial side of the optical fiber bundle 2 is an output end. In other words, at least the input end 21 of the optical fiber bundle 2 is a tapered portion 23, and the output end 22 of the optical fiber bundle 2 may or may not be a tapered portion 23. The optical fiber bundle device 1 is configured so that light from the light source 3 enters the end face 21t of the end 21 on one axial side of the optical fiber bundle 2 (and thus the end face 23t of the tapered portion 23) and exits from the end face 22t of the end 22 on the other axial side of the optical fiber bundle 2.

[0019] 1 and 2, the optical fiber bundle 2 has only one end portion 21 on one axial side and one end portion 22 on the other axial side. The optical fiber bundle device 1 has only one light source 3. Although not shown in the drawings, the optical fiber bundle 2 may have a plurality of end portions 21 on one side in the axial direction by being branched on one side in the axial direction. In this case, the optical fiber bundle device 1 has a light source 3 for each end portion 21 on one side in the axial direction of the optical fiber bundle 2. At least one (preferably all) of the plurality of end portions 21 on one side in the axial direction is a tapered portion 23. Light from each light source 3 enters an end face 21t of the end portion 21 on the one side in the axial direction corresponding to the optical fiber bundle 2, and exits from an end face 22t of the end portion 22 on the other side in the axial direction of the optical fiber bundle 2. And / or, the optical fiber bundle 2 may be branched on the other axial side to have a plurality of end portions 22 on the other axial side.

[0020] 2(b) shows a cross section in a direction perpendicular to the axis of an intermediate portion 24 between the ends 21, 22 on both axial sides of the optical fiber bundle 2. Here, the "direction perpendicular to the axis" refers to a direction perpendicular to the axial direction of the optical fiber bundle 2. 2(b), each of the optical fibers 25 constituting the optical fiber bundle has a core 251 and a clad 252. The clad 252 covers the outer periphery of the core 251. The refractive index n2 of the clad 252 is smaller than the refractive index n1 of the core 251. 2(b), the optical fibers 25 may not be fixed to each other throughout the entire intermediate portion 24. In this case, the optical fiber bundle 2 can be easily bent in any direction. Alternatively, the optical fibers 25 may be fixed to each other (by adhesive or heat fusion) throughout part or the entire intermediate portion 24. As shown in FIG. 2(b), in the intermediate portion 24, it is preferable that the core 251 and the cladding 252 of each optical fiber 25 each have a circular outer edge shape. In the intermediate portion 24, the optical fibers 25 extend parallel to each other in the axial direction.

[0021] In the optical fiber bundle 2, the optical fibers 25 are fixed to each other (by adhesive or by thermal fusion) at the end 22 on the other axial side. An end face 22t of the end 22 on the other axial side of the optical fiber bundle 2 is parallel to the axial direction.

[0022] The optical fiber bundle 2 may further include a tubular member (for example, a tubular member 81, which will be described later with reference to FIG. 4) that covers the outer periphery of the optical fibers 25 in part or all of its axial direction.

[0023] The tapered portion 23 is tapered as shown in Fig. 2(a), Fig. 2(c), and Fig. 2(d), and at least the portion of the tapered portion 23 on the end face 23t side at least on one axial end 21 of the optical fiber bundle 2 is a heat fused portion 26 in which a plurality of optical fibers 25 are heat fused to each other without using an adhesive. Fig. 2(c) shows a cross section of the heat fused portion 26 in the direction perpendicular to the axis. The heat fused portion 26 extends from the end face 23t of the tapered portion 23 to the terminal face 26e of the heat fused portion 26. Here, the "terminal face 26e" of the heat fused portion 26 is a virtual end face parallel to the direction perpendicular to the axis at the position of the heat fused portion 26 farthest from the end face 23t of the tapered portion 23 in the axial direction. In the example of FIG. 2, the end surface 26e of the heat-sealed portion 26 is located between the end surface 23t of the tapered portion 23 and the root surface 23r of the tapered portion 23. However, the end surface 26e of the heat-sealed portion 26 may be located at the root surface 23r of the tapered portion 23. Here, the "root surface 23r" of the tapered portion 23 is a virtual end surface of the tapered portion 23 that is parallel to the axial direction at the position farthest from the end surface 23t of the tapered portion 23 in the axial direction. FIG. 2(d) shows the end surface 23t of the tapered portion 23. The end surface 23t of the tapered portion 23 is parallel to the axial direction. 2(c) and 2(d), the clads 252 of the optical fibers 25 are integrated with each other at the heat fusion part 26. At the heat fusion part 26, the integrated clads 252 cover the cores 251 of the optical fibers 25 and completely or partially fill the gaps between the cores 251. In the optical fiber bundle 2, the optical fibers 25 are heat-fused to each other at the heat-fused portion 26 without using an adhesive, and therefore the heat resistance can be improved compared to a case in which the optical fibers 25 are fixed to each other with an adhesive. In this specification, with respect to the tapered portion 23, “tapered” means that in a cross section taken along the central axis O of the optical fiber bundle 2, the outer peripheral surface 23s of the tapered portion 23 extends linearly from the base surface 23r of the tapered portion 23 to the end surface 23t, so as to move toward the central axis O as it approaches the end surface 23t.

[0024] FIG. 3 shows an enlarged cross section of the heat-sealed portion 26 in the tapered portion 23 along the central axis O. As shown in FIG. 3, in the cross section along the central axis O of the optical fiber bundle 2, in the tapered portion 23 (and thus the heat-sealed portion 26), each interface between each core 251 and the clad 252 is inclined at an acute angle with respect to the central axis O from the base surface 23r of the tapered portion 23 to the end surface 23t, except for the interface on the central axis O of the optical fiber bundle 2, and specifically, extends linearly toward the central axis O toward the end surface 23t. The interface on the central axis O of the optical fiber bundle 2 extends parallel to the axial direction. In addition, in the cross section along the central axis O of the optical fiber bundle 2, in the tapered portion 23 (and thus the heat-sealed portion 26), the inclination angle of each interface between each core 251 and the clad 252 with respect to the central axis O is larger as the interface is located farther from the central axis O. As shown in Figures 2(c) and 2(d), inside the heat-sealed portion 26, the diameter of each core 251 gradually decreases toward the end face 23t of the tapered portion 23. Also, as shown in Figures 2(c) and 2(d), inside the heat-sealed portion 26, the gap g between the cores 251 (and thus the thickness of the cladding 252) gradually decreases toward the end face 23t of the tapered portion 23. Here, the "gap g between the cores 251" is measured at a position where the gap between a pair of adjacent cores 251 is smallest. As shown in Figures 2(c) and 2(d), it is preferable that the tapered portion 23 (and thus the heat-sealed portion 26) has a circular outer edge shape. It is also preferable that each core 251 in the tapered portion 23 (and thus the heat-sealed portion 26) has a circular outer edge shape.

[0025] Each of the optical fibers 25 constituting the optical fiber bundle 2 has a numerical aperture NA of 0.4 or more. The numerical aperture NA of the optical fiber 25 is given by:

number

[0026] The numerical aperture NA of each of the optical fibers 25 constituting the optical fiber bundle 2 can be adjusted by adjusting the composition of the core 251 and the cladding 252 of each of the optical fibers 25 . The core 251 and the clad 252 of each optical fiber 25 constituting the optical fiber bundle 2 may each be made of glass of any composition, such as multi-component glass or quartz glass, or plastic. It is preferable that at least one of the core 251 and the clad 252 of each optical fiber 25 is made of multi-component glass, and it is more preferable that both the core 251 and the clad 252 are made of multi-component glass.

[0027] Since the tapered portion 23 (and thus the heat-sealed portion 26) is tapered and each of the optical fibers 25 constituting the optical fiber bundle 2 has a numerical aperture NA (hereinafter simply referred to as "numerical aperture NA") of 0.4 or more, the optical fiber bundle 2 is configured such that a part of the light incident on the end face 23t of the tapered portion 23 enters the cladding 252 inside the heat-sealed portion 26 of the tapered portion 23 and is then confined in the core 251. This will be described with reference to FIG. As in the case of conventional optical fiber bundles, of the light incident from the light source 3 into the core 251 or clad 252 at the end face 23t of the tapered portion 23, the light whose incident angle (hereinafter referred to as the "initial incident angle") θ1 when it first enters the clad 252 from the core 251 is greater than the critical angle θc of the optical fiber 25 is totally reflected at the interface between the core 251 and the clad 252, and is transmitted within the core 251 while remaining confined therein, and is emitted from the end face 22t of the emission end 22 of the optical fiber bundle 2. Furthermore, as in the case of conventional optical fiber bundles, of the light incident from the light source 3 on the core 251 or the clad 252 at the end face 23t of the tapered portion 23, the light whose initial incident angle θ1 from the core 251 to the clad 252 is equal to the critical angle θc of the optical fiber 25 is transmitted while moving along the interface between the core 251 and the clad 252 (and thus remains confined in the core 251) and is emitted from the end face 22t of the emission end 22 of the optical fiber bundle 2. On the other hand, among the light incident from the light source 3 to the core 251 or the clad 252 at the end face 23t of the tapered portion 23, the light having an initial incident angle θ1 from the core 251 to the clad 252 smaller than the critical angle θc of the optical fiber 25 enters the clad 252 as shown in FIG. 3, and then enters the core 251 adjacent to the clad 252, and then enters the clad 252 a second time. At this time, the incident angle θ2 when entering the clad 252 for the second time (hereinafter referred to as the "second incident angle") is larger than the initial incident angle θ1. If the second incident angle θ2 is equal to or larger than the critical angle θc, the light is confined and transmitted in the core 251, and is output from the end face 22t of the output end 22 of the optical fiber bundle 2. On the other hand, if the second incident angle θ2 is smaller than the critical angle θc, the light enters the clad 252, and then enters the adjacent core 251, and then enters the clad 252 a third time. At this time, the angle of incidence θ3 at the third incidence into the clad 252 (hereinafter referred to as the "third incidence angle") is greater than the second incidence angle θ2. In this manner, the angle of incidence into the clad 252 of the light that has entered the clad 252 after entering the end face 23t of the tapered portion 23 increases each time the light subsequently enters the clad 252. Then, the angle θL at which the light finally enters the clad 252 (hereinafter referred to as the "final incidence angle") of some or all of the light that has entered the clad 252 after entering the end face 23t of the tapered portion 23 becomes equal to or greater than the critical angle θc, and the light is confined and transmitted in the core 251 and emitted from the end face 22t of the emission end 22 of the optical fiber bundle 2. In conventional optical fiber bundles, light that enters the cladding after being incident on the end face of the input end from a light source exits directly to the outside from the outer peripheral surface of the optical fiber bundle, and does not exit from the end face of the output end of the optical fiber bundle. On the other hand, according to the optical fiber bundle of this embodiment, since the tapered portion 23 (and thus the thermally fused portion 26) is tapered and the numerical aperture NA is 0.4 or more, a part of the light incident on the core 251 or the clad 252 at the end face 23t of the tapered portion 23 enters the clad 252 inside the thermally fused portion 26, is confined in the core 251, and is emitted from the end face 22t of the emission end portion 22 of the optical fiber bundle 2. Therefore, the amount of emitted light can be improved accordingly.

[0028] Incidentally, it is preferable that the end face area ratio Rs of the tapered portion 23 is 60% or more. Here, the end face area ratio Rs of the tapered portion 23 is the ratio of the area At of the end face 23t of the tapered portion 23 to the cross-sectional area Ar of the base face 23r of the tapered portion 23 (Rs=(At / Ar)×100[%]). It is practically difficult to make the end face area ratio Rs of the tapered portion 23 less than 60%, since cracks may occur in the tapered portion 23 during the process of forming the tapered portion 23. The higher the end face area ratio Rs of the tapered portion 23, the easier it is to form the tapered portion 23. In addition, when the numerical aperture NA is considered constant, the smaller the end face area ratio Rs of the tapered portion 23, the more light (specifically, light with a wider range of initial incidence angle θ1) of the light that enters the clad 252 after entering the core 251 or the clad 252 at the end face 23t of the tapered portion 23 is confined in the core 251, thereby improving the amount of emitted light. In addition, when the end face area ratio Rs of the tapered portion 23 is considered constant, the higher the numerical aperture NA, the more light (specifically, light with a wider range of initial incidence angle θ1) of the light that enters the clad 252 after entering the end face 23t of the tapered portion 23 is confined in the core 251, thereby improving the amount of emitted light. In other words, the higher the numerical aperture NA, the larger the end face area ratio Rs is, and a certain amount of light of the light that enters the clad 252 after entering the end face 23t of the tapered portion 23 can be confined in the core 251. If the numerical aperture NA is less than 0.4, it can be said that, in theory, if the end face area ratio Rs of the tapered portion 23 is less than 60%, at least a part of the light that enters the cladding 252 after being incident on the end face 23t of the tapered portion 23 may be confined in the core 251. However, as described above, it is practically difficult to make the end face area ratio Rs of the tapered portion 23 less than 60%. According to this embodiment, since the numerical aperture NA is set to 0.4 or more, even if the end face area ratio Rs of the tapered portion 23 is set to a feasible value of 60% or more, at least a part of the light that enters the cladding 252 after being incident on the end face 23t of the tapered portion 23 may be confined in the core 251. From the viewpoint of improving the amount of emitted light, the end face area ratio Rs of the tapered portion 23 is preferably 84% or less, more preferably 82% or less, and even more preferably 80% or less.

[0029] The numerical aperture NA is preferably 0.5 or more, and more preferably 0.564 or more, so that more of the light that enters the cladding 252 after being incident on the end face 23t of the tapered portion 23 is confined in the core 251 (specifically, light having an initial incident angle θ1 within a wider range), thereby improving the amount of emitted light. The numerical aperture NA is more preferably 0.7 or more, and even more preferably 0.764 or more, which allows even more light (specifically, light having an initial incident angle θ1 within a wider range) of the light that enters the cladding 252 after being incident on the end face 23t of the tapered portion 23 to be confined in the core 251, thereby further improving the amount of emitted light. The numerical aperture NA is more preferably 0.8 or more, and even more preferably 0.843 or more, so that of the light that enters the cladding 252 after being incident on the end face 23t of the tapered portion 23, even more light (specifically, light having an initial incident angle θ1 within a wider range) is confined in the core 251, thereby further improving the amount of emitted light.

[0030] In addition, when the end face area ratio Rs of the tapered portion 23 is 60 to 84% and the numerical aperture NA is 0.4 or more, at least light having a cladding incidence angle φ of 1° or less among the light that enters the cladding 252 after being incident on the fiber near the center of the end face 23t of the tapered portion 23 can be confined in the core 251. When the end face area ratio Rs of the tapered portion 23 is 60 to 84% and the numerical aperture NA is 0.5 or more, at least light having a cladding incidence angle φ of 2° or less that enters the cladding 252 after being incident on the fiber near the center of the end face 23t of the tapered portion 23 can be confined in the core 251. When the end face area ratio Rs of the tapered portion 23 is 60 to 84% and the numerical aperture NA is 0.7 or more, at least light having a cladding incidence angle φ of 3° or less that enters the cladding 252 after being incident on the fiber near the center of the end face 23t of the tapered portion 23 can be confined in the core 251. Here, the cladding incident angle φ is the angle of light incident on the cladding 252 at the end face 23t of the tapered portion 23 with respect to the central axis O of the optical fiber bundle at the end face 23t.

[0031] From the viewpoint of improving the amount of emitted light and easiness of forming the tapered portion, the diameter of the end face 23t of the tapered portion 23 is preferably 1.0 to 12.0 mm, and more preferably 2.0 to 10.5 mm. From the standpoint of improving the amount of emitted light and facilitating the formation of the tapered portion, it is preferable that the average value of the diameter of each core 251 at the end face 23t of the tapered portion 23 be 0.8 to 0.4 times the average value of the diameter of each core 251 at the root face 23r of the tapered portion 23, and it is more preferable that it be 0.7 to 0.5 times the average value of the diameter of each core 251 at the root face 23r of the tapered portion 23. From the viewpoint of improving the amount of emitted light and facilitating the formation of the tapered portion, the average value of the diameter of each core 251 at the end face 23t of the tapered portion 23 is preferably 10 to 50 μm, and more preferably 15 to 45 μm. From the standpoint of improving the amount of emitted light and ease of forming the tapered portion, it is preferable that the average value of the spacing g between the cores 251 at the end face 23t of the tapered portion 23 be 0.8 to 0.4 times the average value of the spacing g between the cores 251 at the root face 23r of the tapered portion 23, and it is more preferable that it be 0.7 to 0.5 times the average value of the spacing g between the cores 251 at the root face 23r of the tapered portion 23. From the viewpoint of improving the amount of emitted light and facilitating the formation of the tapered portion, the average value of the spacing g (FIG. 2(d)) between the cores 251 at the end face 23t of the tapered portion 23 is preferably 0.3 to 6.0 μm, and more preferably 0.5 to 5.0 μm. From the viewpoint of improving the amount of emitted light and facilitating the formation of the tapered portion, the taper angle α (FIG. 2(a)) of the tapered portion 23 is preferably 2° to 20°, and more preferably 5° to 15°. Note that the "taper angle α" is the angle of the acute angle side of the outer circumferential surface 23s of the tapered portion 23 with respect to the axial direction. From the viewpoint of improving the amount of emitted light and facilitating the formation of the tapered portion, the axial length L (FIG. 2) of the tapered portion 23 is preferably 0.01 to 40 mm, and more preferably 0.05 to 30 mm. From the viewpoint of improving the amount of emitted light and facilitating the formation of the tapered portion, the axial length M (FIG. 2) of the heat-sealed portion 26 is preferably 0.01 to 40 mm, and more preferably 0.05 to 30 mm.

[0032] The light source 3 may be any light source such as a halogen or metal halide lamp light source, an LED light source, etc. If the light source 3 is a lamp light source, it is preferable because the effect of improving the amount of emitted light described above can be easily obtained.

[0033] Next, an example of a method for forming the tapered portion 23 of the optical fiber bundle 2 of the above-mentioned embodiment will be described with reference to FIG. First, the end 21 of the optical fiber bundle 2 , which is made up of a plurality of optical fibers 25 bundled together, is inserted into the tubular member 81 . The total cross-sectional area of ​​the optical fibers 25 inserted in the tubular member 81 accounts for at least 80% of the inner diameter cross-sectional area of ​​the tubular member 81, and is theoretically less than 90.7% when geometrically calculated. The tubular member 81 is made of, for example, titanium or stainless steel. Titanium has a linear expansion coefficient close to that of the material (for example, glass) constituting the optical fiber 25, and has ductility that allows deformation in the radial direction even if the material has a wall thickness that suppresses deformation in the axial direction of the optical fiber bundle 2 in the temperature range in which deformation occurs by heating. Therefore, titanium is particularly suitable as a material for the tubular member 81. Next, the end 21 of the optical fiber bundle 2 covered with the tubular member 81 is passed through a guide member 83 (FIG. 4(a)), and then, while being heated and pressurized, is pushed into the tapered hole 82h of the jig 82 (FIG. 4(b)). As a result, the end 21 of the optical fiber bundle 2 becomes tapered to form the tapered portion 23, and at least a portion of the tapered portion 23 on the end face side is heat-fused to form the heat-fused portion 26. The tubular member 81 may then be removed from the optical fiber bundle 2, or may remain a component of the optical fiber bundle 2 without being removed thereafter. However, the tapered portion 23 of the optical fiber bundle 2 in the above-described embodiment may be formed by a forming method different from the forming method shown in FIG.

[0034] FIG. 5 is a schematic diagram showing an example of the configuration of the optical fiber bundle device 1 of FIG. 1 when it is configured as an endoscope for industrial or medical use. The optical fiber bundle device 1 configured as an endoscope of this example includes an endoscope scope 4, a light source 3, a control unit 6, and a display 7. The endoscope scope 4 has an operation unit 41 and an insertion unit 42. Inside the insertion unit 42 and the operation unit 41 of the endoscope scope 4, an optical fiber bundle 2 according to an embodiment of the present invention configured as a light guide and an image guide 5 are provided. At the tip of the insertion unit 42 of the endoscope scope 4, for example, the emission end 22 of the optical fiber bundle 2, the incident end of the image guide 5, and an optical system (for example, an objective lens) arranged further on the tip side with respect to the incident end of the image guide 5 are arranged. The optical fiber bundle 2 is configured to transmit light from the light source 3 and irradiate it from the tip of the insertion unit 42 toward an observation object. The tapered portion 23 (and thus the heat-sealed portion 26) constituting the incident end 21 of the optical fiber bundle 2 is disposed opposite the light source 3. The image guide 5 is configured to transmit an image of an object to be observed formed at its incident end, for example, via an optical system (objective lens, etc.). The image transmitted by the image guide 5 is incident on the control unit 6, for example, via an eyepiece (not shown). The control unit 6 is configured to include, for example, a photodetector, an ADC (analog-digital converter), a CPU, and a memory (RAM, ROM, etc.). The control unit 6 performs image processing, etc. based on the image incident from the image guide 5 to generate an image signal, and displays the image of the object to be observed on the display 7 based on the generated image signal. The control unit 6 also controls the light source 3. EXAMPLES

[0035] Experiments were carried out using examples and comparative examples of the present invention, which will be described below. In the optical fiber bundles of Comparative Examples 3 and 4 and Examples 1 to 3, the diameter of each optical fiber 25 in the intermediate portion 24 was 50 μm, the diameter of the core 251 in the intermediate portion 24 was 46 μm, the thickness of the cladding 252 in the intermediate portion 24 was 2 μm, the incident end portion 21 was a tapered portion 23, the diameter of the incident end (end face of the incident end portion 21) was 5 mm, the end face area ratio Rs of the tapered portion 23 was 80%, at least the end face 23t side of the tapered portion 23 was a heat fused portion 26 where the optical fibers 25 were heat fused to each other, the taper angle α was 10°, the output end portion 22 was not a tapered portion 23 but straight along the axial direction, the optical fibers 25 were bonded to each other at the output end portion 22, and the total length was 1000 mm. Four optical fiber bundles were prepared for each of Comparative Examples 3 and 4 and Examples 1 to 3. The tapered portions 23 of the optical fiber bundles of Comparative Examples 3 and 4 and Examples 1 to 3 were formed by the forming method described with reference to Fig. 4. The sum of the cross-sectional areas of the optical fibers 25 inserted into the tubular member 81 before heat fusion was approximately 86% of the inner diameter cross-sectional area of ​​the tubular member 81. The numerical apertures NA of the optical fibers 25 of the optical fiber bundles of Comparative Examples 3 and 4 and Examples 1 to 3 were as shown in Table 1. The optical fiber bundles of Comparative Examples 1 and 2 each had the same configuration as the optical fiber bundles of Comparative Examples 3 and 4 and Examples 1 to 3, except that the incident end 21 was straight along the axial direction instead of the tapered portion 23, the optical fibers 25 were bonded to each other at the incident end 21, and there was no heat fusion portion 26. The diameters of the incident end (end face of the incident end 21) and the exit end (end face of the exit end 22) of the optical fiber bundles of Comparative Examples 1 and 2 were each 5 mm. One optical fiber bundle each of Comparative Examples 1 and 2 was prepared. The incident end 21 of the optical fiber bundles of Comparative Examples 1 and 2 was covered on the outer circumferential side by a tubular member. The sum of the cross-sectional areas of the optical fibers 25 inserted in the tubular member was approximately 86% of the inner diameter cross-sectional area of ​​the tubular member. The numerical aperture NA of each optical fiber 25 of the optical fiber bundles of Comparative Examples 1 and 2 was as shown in Table 1. In the experiment, light from a halogen lamp light source (LS-DWL manufactured by Sumita Optical Glass) was incident on the input end of the optical fiber bundle of each example using an integrating sphere, and the output end of the optical fiber bundle of each example was pressed against an optical power meter (AQ-1135E manufactured by Ando Electric) to measure the amount of output light. The output light amount (light amount) is shown in Table 1. In Table 1, the light amounts of Comparative Examples 3 and 4 and Examples 1 to 3 are the average values ​​of four pieces. The relationship between the numerical aperture NA and the light amount of each example in Table 1 is shown as a graph in FIG. 6.

[0036] [Table 1]

[0037] As can be seen from Table 1 and FIG. 6, in Examples 1 to 3, a significantly larger amount of light was obtained than in Comparative Examples 1 to 4. [Industrial Applicability]

[0038] The optical fiber bundle and optical fiber bundle device of the present invention can be used in any device equipped with an optical fiber bundle and a light source, but is particularly suitable for use in, for example, lighting fixtures or industrial or medical endoscopes. [Explanation of symbols]

[0039] 1 Optical fiber bundle device 2 Optical Fiber Bundle 21 End portion on one side in the axial direction (entrance end portion) 22 End portion on the other side in the axial direction (emission end portion) 21t, 22t end face 23 Tapered section 23s outer surface 23t end face 23r Root surface 24 Middle section 25 Optical Fiber 251 cores 252 Clad 26 Heat fusion part 26e End face 3 light source 4 Endoscope scope 41 Operation section 42 Insertion section 5 Image Guide 6. Control Unit 7. Display 81 Tubular members 82 Jig 82h hole 83 Guide member O Central axis of optical fiber bundle

Claims

1. An optical fiber bundle comprising a plurality of optical fibers, Each of the optical fibers has a core and a cladding, At least one end of the optical fiber bundle in the axial direction is a tapered portion having a tapered shape, an end face of the tapered portion at one end of the optical fiber bundle in the axial direction constitutes an end face of the optical fiber bundle at one end of the optical fiber bundle in the axial direction, At least one end of the optical fiber bundle on one side in the axial direction, at least a portion of the tapered portion on the end face side is a heat fused portion in which the optical fibers are heat fused to each other, Each of the optical fibers has a numerical aperture NA of 0.4 or more; the heat fusion portion of the tapered portion extends to the end face of the tapered portion at one end of the optical fiber bundle in the axial direction, The central axis of the optical fiber bundle extends linearly along the heat-sealed portion, An optical fiber bundle configured such that a portion of light incident on the end face of the tapered portion is confined in the core after entering the cladding inside the thermal fusion portion.

2. 2. The optical fiber bundle according to claim 1, wherein the end portion on the one axial direction side of the optical fiber bundle is an input end portion.

3. 3. The optical fiber bundle according to claim 1, wherein each of the optical fibers has a numerical aperture NA of 0.5 or more.

4. 3. The optical fiber bundle according to claim 1, wherein each of the optical fibers has a numerical aperture NA of 0.7 or more.

5. The optical fiber bundle according to any one of claims 1 to 4, wherein in a cross section along the central axis of the optical fiber bundle, the outer peripheral surface of the tapered portion extends linearly toward the central axis as it approaches the end face of the tapered portion, all the way up to the end face of the tapered portion.

6. 6. The optical fiber bundle according to claim 1, wherein inside said heat-sealed portion, a diameter of each of said cores gradually decreases toward said end face of said tapered portion.

7. The optical fiber bundle according to any one of claims 1 to 6, wherein at least a portion of the light that is incident on the end face of the tapered portion and has an initial angle of incidence from the core to the cladding that is smaller than a critical angle of the optical fiber has an incident angle to the cladding that increases within the tapered portion each time the light is incident on the cladding, and a final incident angle when the light finally enters the cladding becomes equal to or greater than the critical angle, and the light is confined to the core.

8. The optical fiber bundle according to any one of claims 1 to 7, A light source; Equipped with An optical fiber bundle device configured so that light from the light source is incident on the end face of the tapered portion at one end of the optical fiber bundle in the axial direction.

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