Light diffusion device

Abstract

Provided is a light diffusion device that enables laser light of large light intensity to be emitted in a longer region in a light emission part.　This light diffusion device is provided with an optical fiber (20) comprising a core (21) positioned on the center side in the radial direction, and a cladding (22) positioned on the outer peripheral side of the core (21), and the light diffusion device emits light incident from the proximal-end part of the optical fiber (20) from the vicinity of the distal-end part of the optical fiber, the light diffusion device having a light transmission part that transmits light incident from the proximal-end part toward a distal-end part (20 TE), and a light emission part (20b) in which portions positioned on the outer peripheral side of the cladding (22) are removed in the vicinity of the distal-end part, and the light diffusion device having a region in which the increase rate of the optical loss with respect to the distance z from the end part (23BE) on the proximal-end part side B in the light emission part (20b) is smaller relative to the proximal-end part side B.

Description

Light Diffuser

[0001] The present invention relates to a light diffusion device.

[0002] A known conventional light diffusing device includes an optical fiber having a core located radially toward the center and a cladding located on the outer periphery of the core, and emits laser light incident on a base end of the optical fiber from a tip end of the optical fiber and an outer periphery near the tip end (see, for example, Patent Document 1). The optical fiber of the conventional light diffusing device has a light transmitting section that transmits the laser light incident on the base end, and a light emitting section near the tip end that emits the laser light transmitted through the light transmitting section.

[0003] In photoimmunotherapy, a cancer treatment method, a light diffusion device is used to insert the tip of an optical fiber into the human body and irradiate laser light onto a drug that has been administered to the human body and reached cancer cells. Light diffusion devices are also used by inserting them into the body together with endoscopes such as gastroscopes and catheters to irradiate the inside of the body or project light onto the body surface from inside the body.

[0004] Conventional light diffusion devices partially remove the cladding near the tip of the optical fiber to expose the core, thereby emitting light from the outer peripheral surface of the light emitting portion. If the cladding near the tip of the light emitting portion is uniformly removed, the laser light emitted from the most proximal end of the light emitting portion will become increasingly weaker as it moves toward the tip. In light diffusion devices, it is desirable to ensure a certain length of the region from which the laser light is emitted in the light emitting portion in order to improve the efficiency of treatment and ensure a large irradiation area.

[0005] A technology has been disclosed in which recesses (grooves) extending in the circumferential direction are periodically formed in the longitudinal direction in the portion of the light emitting section located on the outer periphery of the cladding, and the depth or width of the groove increases depending on the distance from the base end side (see Patent Document 2). For ease of explanation, the following description will focus on the depth of the groove, but the same applies to the width of the groove.

[0006] In the technology described in Patent Document 2, the emission of laser light is suppressed at the end on the base end side where the groove depth is smallest, and the groove depth gradually increases, making it easier for the laser light to reach the tip end of the light emitting portion. Therefore, according to the technology described in Patent Document 2, it is possible to lengthen the emission region of the laser light.

[0007] However, if the groove depth is gradually increased with distance from the base end to extend the laser light emission area, the light intensity distribution becomes broader, and the laser light output tends to be insufficient in the areas closer to the base end and the area closer to the tip end. For example, when irradiating a drug that has reached cancer cells with laser light, irradiating the cancer cells with laser light with insufficient light intensity will not be effective, and it is desirable to avoid irradiating areas other than the cancer cells as much as possible. Furthermore, in any application, if there are many areas where laser light with insufficient light intensity is emitted, irradiation from those areas is wasted, which is undesirable from the perspective of effective energy utilization.

[0008] If the optical loss is increased more rapidly with distance from the end portion on the proximal side in order to make the optical intensity distribution steeper and reduce the area where laser light with insufficient optical intensity is emitted, the peak of optical intensity shifts toward the proximal side, which makes it difficult for the laser light to reach the distal end of the light emitting portion, thereby defeating the intended purpose of extending the laser light emission area.

[0009] Special table 2001-502438 publication Special table 2022-503332 publication

[0010] Therefore, an object of the present invention is to provide a light diffusing device capable of emitting laser light with high light intensity over a longer area in a light emitting portion.

[0011] The above object can be achieved by the present invention, which is described below.

[0012] <1> A light diffusion device comprising an optical fiber having a core located radially toward the center and a clad located on the outer periphery of the core, wherein light incident from a base end of the optical fiber is emitted from the vicinity of a tip end of the optical fiber, the light diffusion device comprising: a light transmitting section that transmits the light incident from the base end toward the tip end; and a light emitting section in which a portion located on the outer periphery of the clad near the tip end has been removed, wherein the light emitting section has a region in which the rate of increase in light loss with respect to distance from an end on the base end side is smaller than that on the base end side.

[0013] <2> The light diffusion device described in <1>, wherein in the light output section, grooves extending in the circumferential direction are formed periodically in the longitudinal direction in a portion located on the outer periphery of the cladding, at least one of the depth and width of the grooves gradually increases from the end on the base end side toward the tip end, and the rate of increase of at least one of the depth and width of the grooves with respect to the distance from the end on the base end side of the light output section is smaller in the region than in the region on the base end side.

[0014] <3> The light diffusing device according to <2>, wherein an increasing rate of the depth or width of the groove with respect to the distance from the end on the base end side of the light emitting portion is smaller in the region than in the region on the tip end side.

[0015] <4> The light diffusing device according to any one of <1> to <3>, wherein the optical fiber is made of quartz.

[0016] <5> The light diffusing device according to <1>, wherein a portion of the light emitting portion located on an outer periphery side of the cladding is roughened.

[0017] <6> The light diffusing device according to <1>, wherein the light emitting portion has two or more regions where the rate of increase in light loss with respect to distance from the end on the base end side is smaller than that on the base end side.

[0018] According to the present invention, it is possible to provide a light diffusing device capable of emitting laser light with high light intensity over a longer region in the light emitting portion.

[0019] 7 is a schematic diagram of a light diffusing device according to an embodiment that is an exemplary aspect of the present invention. FIG. 8 is a cross-sectional view of a light output portion of an optical fiber and its vicinity in a light diffusing device according to an embodiment that is an exemplary aspect of the present invention. FIG. 9 is an enlarged cross-sectional view of a portion of the light output portion of the optical fiber of FIG. 2. FIG. 10 is a graph showing the relationship between the distance from the base end and the groove depth for light output portions with three different tapered structures. FIG. 11 is a graph showing the relationship between the distance from the base end and the groove depth for light output portions with three different tapered structures, including the structure of this embodiment. FIG. 12 is a graph showing the relationship between the distance from the base end and the light intensity for light output portions with three different tapered structures, including the structure of this embodiment. FIG. 13 is a graph showing the relationship between the highest light intensity in each tapered structure, taken as 1, in the results shown in FIG. 7. FIG. 14 is a cross-sectional view of a light output portion of an optical fiber in a light diffusing device according to Modification 1 that is an exemplary aspect of the present invention. FIG. 15 is a cross-sectional view of a light output portion of an optical fiber and its vicinity in a light diffusing device according to Modification 2 that is an exemplary aspect of the present invention. 10 is a graph showing the relationship between the distance from the base end and the optical loss for a light emitting portion whose tapered structure is controlled so as to have two optical loss increase rate decreasing regions.

[0020] Hereinafter, a light diffusing device according to an embodiment of the present invention will be specifically described with reference to the drawings. In the following description, a light diffusing device 1 according to an embodiment for explaining the basic concept of the present invention will be first described in detail, and then two modifications, namely, Modification 1 and Modification 2, will be described.

[0021] 1 is a schematic diagram of a light diffusing device 1 according to an embodiment, and Fig. 2 is a cross-sectional view of a light emitting portion and its vicinity of an optical fiber in the light diffusing device 1. The base end side of the optical fiber is indicated by an arrow B, and the tip end side is indicated by an arrow T (the same applies to drawings showing light diffusing devices or parts thereof, including light diffusing devices other than those of the embodiment).

[0022] The light diffusion device 1 is a device that emits light incident from a base end 20BE of an optical fiber 20 from a tip vicinity 20TN, and a light source (not shown) for generating light is connected to the base end 20BE on the base end side B of the optical fiber 20 via a connector 10. In the light diffusion device 1 of this embodiment, a glass cap 11 is placed over the tip vicinity TN of the optical fiber 20, and the area of ​​the optical fiber 20 other than the tip vicinity TN is covered with a nylon jacket 12.

[0023] A buffer layer 13 made of fluororesin is interposed between the optical fiber 20 and the jacket 12 to bond the jacket and the optical fiber together, and the optical fiber 20 is protected by the jacket and the buffer layer.

[0024] In this embodiment, the outer diameter of the jacket 12 is approximately 1.5 mm, the length of the light diffusion device 1 (including the connector 10) is approximately 2000 mm, and the outer diameter of the glass cap 11 is approximately 1.5 mm and the length is approximately 65 mm. Of course, these dimensions are merely examples, and the present invention is not limited to these.

[0025] The light source generates visible light or laser light. When generating laser light, the light source has a semiconductor laser, and generates laser light by passing electricity through the semiconductor laser to cause laser oscillation. The light source generates, for example, red laser light having a wavelength of 670 nm or more and 700 nm or less.

[0026] Optical fibers are generally made of resin (plastic) or quartz members, but the optical fiber 20 in this embodiment is made of quartz members. As shown in Figures 2 and 3, the optical fiber 20 is a single-core optical fiber made of a core 21 located radially toward the center and a cladding 22 located on the outer periphery of the core 21. In the optical fiber 20, the relative refractive index difference between the core 21 and the cladding 22 is, for example, 2% or more and 11% or less.

[0027] For example, the outer diameter of the cladding 22 of the optical fiber 20 is preferably 250 μm or more and 1000 μm or less. Also, the outer diameter of the core 21 of the optical fiber 20 is preferably 200 μm or more and 1000 μm or less. The thickness of the cladding 22 is preferably 5 μm or more and 100 μm or less.

[0028] The numerical aperture (NA) of the optical fiber 20 used is preferably 0.5 or more, and more preferably 0.6 or more. By using an optical fiber 20 with an appropriately large numerical aperture, light can be made to enter the optical fiber 20 at a wide angle in advance, which makes it easier for the light to be emitted from the entire circumferential surface, which, combined with the effect of making the cladding thinner, makes it easier to achieve side emission.

[0029] As shown in FIG. 1, the optical fiber 20 has a light transmitting section 20a that transmits the laser light incident from the base end 20BE toward the tip end side T, and a light emitting section 20b that emits the laser light transmitted through the light transmitting section 20a from the outer surface by removing a portion located on the outer periphery of the cladding 22 within a predetermined range in the extension direction of the tip end side T.

[0030] 2, the optical fiber 20 is exposed beyond the buffer layer 13 exposed from the end of the jacket 12 on the tip side T. The exposed buffer layer 13 is fitted over the opening on the base side B of the glass cap 11 so as to cover it. In this embodiment, the length of the buffer layer 13 in the longitudinal direction BT is about 1 to 2 mm, and it is preferable that the buffer layer 13 does not extend all the way into the glass cap 11. The buffer layer 13 and the glass cap 11 are fixed together with an adhesive.

[0031] 2 , in the present embodiment, the light emitting portion 20b of the optical fiber 20 has circumferentially extending grooves 23 periodically formed in the longitudinal direction (which is the same as the arrow direction on the base end side B and the arrow direction on the tip end side T, and will therefore be referred to as the "longitudinal direction BT" hereinafter) in a portion located on the outer periphery of the cladding 22. The groove 23 is a bottomed groove, and is a single groove that is connected in a spiral shape from the base end side B to the tip end side T. In the present embodiment, the outer diameter of the cladding 22 of the optical fiber 20 is 788 μm, and the length of the light emitting portion 20b in which the grooves 23 are provided in the longitudinal direction BT is 30 mm.

[0032] In order to avoid any influence of the adhesive that fixes the buffer layer 13 and the glass cap 11, it is preferable that the optical fiber 20 exposed from the buffer layer 13 has a base-side unprocessed region 25 at a certain distance in the longitudinal direction BT, and that the groove 23 is provided on the tip end side T of the base-side unprocessed region 25. In this embodiment, it is preferable that the base-side unprocessed region 25 has a length of, for example, about 3 to 4 mm.

[0033] Fig. 3 shows a further enlarged view of a portion of the light emitting portion 20b of the optical fiber 20. As shown in Fig. 3, the depth (d) of the groove 23 gradually increases (d1 < d2 < d3 < d4) from the end on the base end side B (the position indicated by reference numeral 23BE in Fig. 2; hereinafter referred to as the "base end side end") toward the tip end TE. Note that, as shown in Fig. 3, if the bottom 23b of the groove 23 is inclined, the depth at its center position is defined as the depth (d) of the groove 23 (hereinafter, sometimes simply referred to as "depth (d)").

[0034] 3, the depth (d) increases uniformly with respect to the distance (z) from the proximal end 23BE, i.e., the rate of increase is constant. In other words, the depth (d) gradually increases from the proximal end 23BE toward the distal end TE at a constant taper.

[0035] As shown in FIG. 3, a straight line L connecting the bottom 23b of the groove 23 ２３ｂ and the line L connecting the outer peripheral surface 24 of the clad 22 between the grooves 23. ２４The angle θ formed with the center line 23b (parallel to the longitudinal direction BT) is an index showing the magnitude of the taper of the depth (d) of the groove 23. In this embodiment, the bottom 23b of each groove 23 is inclined, forming a linear taper overall, but if, for example, the depth of the bottom 23b of each groove 23 is constant and the depth (d) changes in a stepped manner overall, it is only necessary to find the angle θ formed by the line connecting the centers of each groove 23 in the longitudinal direction BT.

[0036] If this angle θ is small, the change (increase) in the depth (d) with respect to the distance (z) from the base end side end 23BE will be more gradual, and conversely, if the angle θ is large, the change (increase) in the depth (d) with respect to the distance (z) from the base end side end 23BE (hereinafter sometimes simply referred to as "distance (z)") will be more rapid.

[0037] In the light diffusing device 1 according to this embodiment, when a light source (not shown) is activated to irradiate laser light from the base end 20BE of the optical fiber 20, the laser light is transmitted through the light transmitting section 20a and emitted from the light emitting section 20b having a groove 23 formed on the outer periphery. At this time, emission of the laser light is most suppressed at the base end 23BE, which has the smallest depth (d), and as it advances toward the tip end side T, the depth (d) gradually increases, making it easier for the laser light to reach the tip end side T of the light emitting section 20b.

[0038] The light output section 20b has three tapered structures: "Tapered Structure 1," in which the taper (angle θ) is large and the depth (d) is greatest (122 μm) at the tip 20TE; "Tapered Structure 2," in which the taper (angle θ) is small and the depth (d) at the tip 20TE is half that of Tapered Structure 1 (61 μm); and "Uniform Structure," in which the depth (d) is uniform from the base end 23BE to the tip 20TE and is equal to the maximum value (122 μm) in Tapered Structure 1. The distribution of light intensity as a function of distance (z) from the base end 23BE will be examined below.

[0039] It is believed that as the depth d (μm) of the groove 23 increases, the light loss (1 / cm) also increases proportionally. In this embodiment, the light loss (1 / cm) is calculated using the following formula: Light loss (1 / cm) = 100 × groove depth (m) Light loss (1 / cm) × 100 = groove depth (μm) Therefore, 100 times the value shown as light loss (including in graphs) below represents the actual groove depth d (μm) in verification of this embodiment.

[0040] 4 is a graph showing the relationship between the distance z (μm) from the base end 23BE and the optical loss for the light output portion 20b with three different tapered structures. The graph in FIG. 4 is plotted with the distance z (μm) from the base end 23BE on the horizontal axis and the optical loss on the vertical axis. The slope of the graph represents the magnitude of the taper (angle θ).

[0041] Figure 5 is a graph showing the relationship between the distance z (μm) from the base end 23BE and the light intensity (standardized value) when laser light is incident on the base end 20BE and emitted from the outer peripheral surface of the light emitting portion 20b for a light diffusion device 1 having a light emitting portion 20b with three tapered structures similar to those shown in Figure 4. The graph in Figure 5 is plotted with the distance z (μm) from the base end 23BE on the horizontal axis and the light intensity (standardized value) on the vertical axis. The light intensity here refers to the lateral irradiation intensity per 100 μm length when the input light is set to 1.0.

[0042] From the graph in Figure 5, it can be seen that the light loss is first large from the base end side end 23BE, and then in the uniform structure, the light intensity is greatest at the base end side end 23BE and quickly attenuates as the distance z (μm) increases.

[0043] Furthermore, if the optical loss is made to increase more gradually with distance (z) in order to lengthen the laser light emission area, as in the tapered structure 2, the distribution of light intensity becomes broad, and the laser light output is likely to be incomplete in the area closer to the base end 23BE or the area closer to the tip 20TE.

[0044] Furthermore, if the optical loss increases more rapidly with distance (z) so that the optical intensity distribution becomes steeper, as in the case of tapered structure 1, the peak of the optical intensity shifts to the base end side B. As a result, it becomes difficult for the laser light to reach the tip end 20TE of the light emitting portion 20b, and the optical intensity gradually decreases from the middle as shown in FIG.

[0045] Therefore, in this embodiment, the depth (d) with respect to the distance (z) is adjusted so that there is a region in the light emitting portion 20b where the rate of increase of the depth (d) with respect to the distance (z) from the base end portion 23BE is smaller than on the base end portion B or the tip end portion T. That is, the rate of increase of light loss is large up to a certain distance from the base end portion 23BE (region Ab, described later), the rate of increase of light loss is kept small in the next region (region Ax, described later), and then the rate of increase of light loss becomes large again from that region toward the tip end portion T (region At, described later).

[0046] The distribution of light intensity as a function of distance (z) from the base end 23BE for the light emitting portion 20b of three tapered structures, namely, "Tapered Structure 3" in which the taper (angle θ) is even larger than that of Tapered Structure 1 and the depth (d) at the tip 20TE is even larger (200 μm), "Uniform Structure" similar to that of Figure 4, and the structure of this embodiment, will be examined below.

[0047] 6 is a graph showing the relationship between the distance z (μm) from the base end 23BE and the optical loss for the light output portion 20b having three different tapered structures, including the structure of this embodiment. The graph in FIG. 6 is plotted with the distance z (μm) from the base end 23BE on the horizontal axis and the optical loss on the vertical axis. The slope of the graph represents the magnitude of the taper (angle θ).

[0048] In tapered structure 3, the taper (angle θ) is larger than in tapered structures 1 and 2, and therefore the slope of the graph is also larger (see the graph in FIG. 4). In all of tapered structures 1 to 3, the optical loss increases linearly with the distance z (μm). That is, in all of tapered structures 1 to 3, the rate of increase in optical loss with respect to the distance z (μm) is 0 (zero).

[0049] On the other hand, in the structure of this embodiment, the rate of increase in light loss is large (the slope of the graph is steep) in region Ab up to 5000 μm from the base end 23BE, and is small (the slope of the graph is shallow) in the next region Ax, where the rate of increase in light loss is suppressed, and then the rate of increase in light loss becomes large again in region At on the tip end side T of region Ax. In other words, the rate of increase in light loss with respect to the distance (z) from the base end side 23BE in light emitting portion 20b is smaller in region Ax than on the base end side B of region Ax (i.e., region Ab), and is smaller in region Ax than on the tip end side T of region Ax (i.e., region At).

[0050] 7 is a graph showing the relationship between the distance z (μm) from the base end 23BE and the light intensity (standardized value) when laser light is incident on the base end 20BE and emitted from the outer peripheral surface of the light emitting portion 20b for a light diffusion device 1 having a light emitting portion 20b with three different tapered structures, including the same embodiment structure as in FIG. 6. The graph in FIG. 7 is plotted with the distance z (μm) from the base end 23BE on the horizontal axis and the light intensity (standardized value) on the vertical axis. The light intensity here refers to the lateral irradiation intensity per 100 μm length when the input light is set to 1.0.

[0051] 7, in the structure of this embodiment, the graph has two peaks, one where the distance z is between 5000 and 10000 μm and the other where the distance z is between 10000 and 15000 μm, indicating that a relatively wide region of high light intensity exists.

[0052] Figure 8 shows a graph in which the highest light intensity for each tapered structure is set to 1 for the results shown in Figure 7. For example, when using laser light to irradiate a drug that has reached cancer cells, a certain level of light intensity is required. Here, as an example, the required light intensity is set to 0.8 or more in the graph of Figure 8.

[0053] The region where a light intensity of 0.8 is ensured is the range indicated by the double-headed arrow a1, which includes the region between 5000 and 15000 μm, and is a relatively wide range (hereinafter, the region in this embodiment structure where the light intensity is 0.8 or more, which includes the region between 5000 and 15000 μm, will be referred to as the "flat region a1").

[0054] On the other hand, it is better to narrow the region of insufficient light intensity below 0.8. For example, if the base region a2 is defined as a region with a light intensity of 0.1 with a wider base, in the structure of this embodiment, the flat region a1 occupies approximately 45% of the base region a2.

[0055] In contrast, in the tapered structure 3, the range of the region b1 where a light intensity of 0.8 is ensured is not significantly different from the flat region a1 of the structure of this embodiment, as shown in Figure 8, but the light intensity is broadly spread on both the base end side B and the tip end side T of the region b1 (especially the latter). In the tapered structure 3, the bottom region b2 where a light intensity of 0.1 is ensured has a longer range than the bottom region a2 of the structure of this embodiment. Therefore, in the tapered structure 3, the region b1 where a light intensity of 0.8 is ensured is only about 36% of the bottom region b2.

[0056] As described above, in this embodiment, the optical loss with respect to the distance (z) is adjusted so as to create a region Ax in which the rate of increase in optical loss with respect to the distance (z) from the base end 23BE in the light emitting portion 20b is smaller than on the base end side B or the tip end side T, and therefore laser light of high optical intensity can be emitted over a longer region in the light emitting portion 20b. Furthermore, in this embodiment, the optical intensity drops relatively sharply on the base end side B or the tip end side T, which are regions from which laser light of high optical intensity can be emitted, so there is little wasted energy and it is possible to suppress irradiation of light of relatively low optical intensity to locations other than the target.

[0057] In this embodiment, the depth (d) of the groove 23 can be measured by, for example, cutting a cross section of the portion to be measured (for example, dashed-dotted line X in FIG. 3 ) and directly measuring the depth of the groove 23 (depth d2 in the cross section of dashed-dotted line X) with a microscope. Alternatively, the depth can be measured non-destructively with a laser microscope.

[0058] (Modification 1) Fig. 9 is a cross-sectional view of the light emitting portion 120b of the optical fiber in the light diffusing device according to Modification 1. Note that the glass cap is not shown in Fig. 9. The overall configuration of the light diffusing device in this modification is the same as that of the above embodiment, so please refer to Fig. 1 in the above embodiment.

[0059] Modification 1 differs from the above embodiment in that a non-processed region 125 is provided midway in the longitudinal direction BT of the light emitting portion 120b, where no groove 23 is provided. Since the other configurations of Modification 1 are the same as those of the above embodiment, the same reference numerals as those of the above embodiment are used in Figure 9, and detailed description thereof will be omitted.

[0060] As in the above embodiment, the light output portion 120b has its light loss adjusted with respect to the distance (z) so that there is a region (in the above embodiment, this region is represented by the symbol Ax, and will also be represented by the symbol Ax in this modified example) in which the rate of increase in light loss with respect to the distance (z) from the base end portion 23BE in the light output portion 120b is smaller than that on the base end side B or the tip end side T. The midpoint unprocessed region 125 is provided between the region Ax and the tip end side T.

[0061] In the light emitting portion 120b, the depth (d) of the groove 23 gradually increases from the base end 23BE toward the tip end TE, so that the bottom of the groove 23 gets closer to the core 21 as it approaches the tip end TE. That is, in the light emitting portion 120b, the resistance to bending decreases as it approaches the tip end TE. In particular, the region Ax where the taper changes and between the tip end side T thereof tend to become brittle.

[0062] In this modification, resistance to bending is increased by providing a no-processing region 125 between this region Ax that is prone to becoming brittle and the tip end side T. Since the other configurations are the same as those of the above embodiment, this modification also makes it possible to emit laser light with high light intensity over a longer region in the light emitting portion 120b, thereby reducing energy waste and suppressing irradiation of light with a relatively low light intensity to locations other than the target.

[0063] (Modification 2) Fig. 10 is a cross-sectional view of the light emitting portion 120b of the optical fiber and its vicinity in a light diffusing device according to Modification 2. Note that the glass cap is not shown in Fig. 10. The overall configuration of the light diffusing device in this modification is the same as that of the above embodiment, so please refer to Fig. 1 in the above embodiment.

[0064] In Modification 2, the optical fiber 220 is made of a resin (plastic) member. Specifically, as shown in Fig. 10 , the optical fiber 220 is a single-core optical fiber made of a resin (plastic) core 221 located on the radial center side and a resin (plastic) cladding 222 located on the outer periphery of the core 221.

[0065] Furthermore, in Modification 2, instead of providing a groove in a portion of light emitting portion 220b located on the outer periphery side of clad 222, clad 222 is roughened to expose core 221, and roughened surface 223 is formed by roughening up to the surface of core 221. The length in the longitudinal direction BT of light emitting portion 220b on which roughened surface 223 is formed is, for example, about 10 mm to 100 mm.

[0066] In the second modification, the depth of the roughened recess on the surface of the core 221 gradually increases from the base end 223BE toward the tip 220TE. The rate of increase in the depth of the roughened recess with respect to the distance from the base end 223BE (i.e., the rate of increase in light loss) is large up to a certain distance from the base end 223BE, then the rate of increase in light loss is kept small in the next region, and then the rate of increase in light loss increases again from that region toward the tip end T (this change in the rate of increase is small and does not appear in FIG. 10 ).

[0067] As in this modification, the light diffusing device according to the present invention can also be obtained by roughening the cladding 222 and the core 221. Note that by reducing the diameter of the core 221 to ¾ or less, the frontal component emitted from the front of the tip end face of the optical fiber 220 can be reduced. Since the rest of the configuration is the same as in the above embodiment, this modification also allows for the emission of laser light with high light intensity over a longer region of the light emitting portion 120b, resulting in less wasted energy and suppressing the irradiation of light with a relatively low light intensity on areas other than the target.

[0068] The above-described embodiments and modifications merely show typical examples of the present invention, and the present invention is not limited to these embodiments. That is, a person skilled in the art can implement various modifications in accordance with conventionally known knowledge without departing from the gist of the present invention. As long as such modifications still have the configuration of the light diffusion device of the present invention, they are of course included in the scope of the present invention.

[0069] For example, in the above embodiment and Modification 1, the depth (d) of the groove 23 gradually increases from the base end 23BE toward the distal end TE, but the present invention is not limited to this, and the groove width may also gradually increase. In this case, it is considered that as the groove width increases, the light loss (1 / cm) also increases proportionally, and this can be verified in the same way as the depth (d) of the groove 23, and the same functions and effects of the present invention are achieved.

[0070] Furthermore, both the depth and width of the groove may be varied. In this case, the cross-sectional area of ​​the groove, calculated by multiplying the groove depth by the width, may be adjusted to gradually increase from the base end toward the tip. That is, the cross-sectional area of ​​the groove with respect to distance may be adjusted so that a region is created in which the rate of increase in the cross-sectional area of ​​the groove with respect to distance from the base end in the light-emitting portion is smaller than that on the base end or tip end. Therefore, it is sufficient that at least one of the depth and width of the groove gradually increases from the base end toward the tip, and that there is a region in which the rate of increase in at least one of the depth and width of the groove with respect to distance from the base end in the light-emitting portion is smaller than that on the base end.

[0071] In any case, in the present invention, the light loss with respect to distance is adjusted so that there is an area in the light emitting section where the rate of increase in light loss with respect to distance from the base end side is smaller than on the base end side or the tip end side.

[0072] Furthermore, in the above embodiments and variants, and further in the above explanation, examples are given in which the light loss with respect to distance is adjusted so that an area is created in which the rate of increase in light loss with respect to distance from the base end side end of the light emitting section is smaller than both the base end side and the tip end side, but this area does not necessarily have to be smaller than the tip end side.

[0073] That is, in the present invention, depending on the desired performance and various conditions, it is sufficient to adjust the optical loss with respect to distance so that a region is created in which the rate of increase in optical loss with respect to distance from the base end side of the light emitting portion is smaller than at least the base end side. If a region is created in which the rate of increase in optical loss with respect to distance from the base end side is smaller than at least the base end side, a region equivalent to the "flat region" is formed, and laser light with high optical intensity can be emitted over a long region of the light emitting portion.

[0074] In the above embodiment and modified example, and further in the above description, an example is given in which there is one region in which the rate of increase in light loss with respect to the distance from the base end of the light emitting portion is smaller than that on the base end side, but it is also a preferred embodiment to have two or more such regions. More specifically, it is also a preferred embodiment to have two or more regions (hereinafter referred to as "light loss increase rate decreasing regions") in which the "rate of increase in light loss with respect to the distance from the base end of the light emitting portion" is smaller in a certain region than in the region on the base end side of that region.

[0075] Fig. 11 is a graph showing the relationship between the distance z from the base end and the optical loss for a light output section whose tapered structure is controlled to have two optical loss increase rate decreasing regions. The graph in Fig. 4 is a graph with the distance z from the base end on the horizontal axis and the optical loss on the vertical axis, but it is a conceptual graph with no scale on either axis. As in Fig. 4, the slope of the graph represents the magnitude of the taper (angle θ). Of course, as explained above, optical loss may be controlled by factors other than the magnitude of the taper (angle θ).

[0076] As shown in the graph of FIG. 11, the region Ab starting from the base end side has a large increase rate of optical loss (the slope of the graph is steep), and the next region Ax １ In the region Ax ２ In the region Ax, the increase rate of the optical loss is smaller (the slope of the graph is smaller). ２In the region At closer to the tip end T, the rate of increase in optical loss again becomes larger.

[0077] In other words, the rate of increase in light loss with respect to the distance (z) from the base end side end in the light emitting portion is １ The area Ax is larger than the base end side (i.e., the area Ab) of the １ is smaller, so the area Ax １ The increase rate of optical loss with respect to the distance (z) from the end on the base end side in the light emitting portion is in the region Ax ２ the base end side (i.e., area Ax １ ) compared to the area Ax ２ is smaller, so the area Ax ２ 11 is a region where the optical loss increase rate decreases. Therefore, the configuration of the light output portion shown in the graph of FIG.

[0078] As described above, by providing two optical loss increase rate reducing regions, the radiation pattern from the light output portion of the optical fiber can be made flatter. The number of optical loss increase rate reducing regions is not limited to one or two, but may be three or more.

[0079] 1: Light diffusion device, 10: Connector, 11: Glass cap, 12: Jacket, 13: Buffer layer, 20: Optical fiber, 20a: Light transmission section, 20b, 120b, 220b: Light emission section, 20BE: Base end section, 20TE, 220TE: Tip end section, 21, 221: Core, 22, 222: Cladding, 23: Groove, 23b: Bottom, 23BE, 223BE: Base end side end section, 24: Outer circumferential surface, 25: Base end side unprocessed region, 125: Midway unprocessed region, 223: Roughened surface

Claims

1. A light diffusion device comprising an optical fiber consisting of a core located radially inward and a cladding located on the outer periphery of the core, wherein light incident from the base end of the optical fiber is emitted from the vicinity of the tip end of the optical fiber, the light diffusion device comprising: a light transmitting section that transmits the light incident from the base end toward the tip end; and a light emitting section in which the portion located on the outer periphery of the cladding near the tip end has been removed, the light emitting section having an area in which the rate of increase in light loss with distance from the end on the base end side is smaller than that on the base end side.

2. A light diffusion device as described in claim 1, wherein in the light output section, circumferentially extending grooves are formed periodically in the longitudinal direction in a portion located on the outer periphery of the cladding, and at least one of the depth and width of the grooves gradually increases from the end on the base end side toward the tip end, and the rate of increase of at least one of the depth and width of the grooves with respect to the distance from the end on the base end side of the light output section is smaller in the region than in the region on the base end side.

3. The light diffusing device according to claim 2, wherein the rate of increase in the depth or width of the groove relative to the distance from the end on the base end side of the light emitting portion is smaller in the region than in the tip end side of the region.

4. The light diffusing device according to any one of claims 1 to 3, wherein the optical fiber is made of quartz.

5. The light diffusing device according to claim 1, wherein the portion of the light emitting portion located on the outer periphery of the cladding is roughened.

6. The light diffusing device according to claim 1, wherein the light emitting section has two or more regions where the rate of increase in light loss with distance from the base end is smaller than that on the base end side.

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