Optical fiber having convex surface at tip end

Abstract

To provide a plastic optical fiber with a convex surface formed on a tip end that attains compatibility between a wide irradiation range and illuminance uniformity.SOLUTION: There is provided a plastic optical fiber having a convex surface at a tip end in which: an irradiation angle θmax of a light beam widening most widely in an irradiation angle θ being an angle between the light beam emitted from the optical fiber and a center axis of the optical fiber is 60 degrees or more; a luminance L1 at an arbitrary measurement distance from the tip end of the optical fiber in a range where the irradiation angle θ of the optical fiber is 0 degrees to 50 degrees is (L1>Lmax×0.8) with respect to a maximum luminance Lmax in a whole irradiation range at the measurement distance of the optical fiber; and a luminance L2 at the measurement distance at a position where the irradiation angle θ of the optical fiber is 60 degrees is (L2>Lmax×0.4) with respect to the maximum luminance Lmax.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber with a processed end face, and to an endoscopic illumination device, an ophthalmic surgical illumination probe, and a vascular catheter that use the optical fiber. [Background technology]

[0002] In endoscopic surgery and ophthalmic surgery, a common method is to observe the affected area by irradiating light from one end of an optical fiber and then irradiating it from the exit end face. The larger the angle of light irradiation, the wider the area around the affected area can be observed, so optical fibers with a large numerical aperture are preferably used. Effective methods for further expanding the light irradiation range include installing a lens near the exit end face or processing the end face by heating or cutting. However, lenses are generally expensive, and their use complicates the design, so optical fiber end face processing, which is easy to process, is preferably used.

[0003] A method for forming a lens shape on the end face of an optical fiber has been proposed, which includes the steps of: (a) preparing a plastic optical fiber with an exposed end of a predetermined length; (b) pressing a heated lens-forming mold against the tip of the end of the plastic optical fiber to soften and melt a part or the whole of the end and form the tip of the end into a lens shape; and (c) rapidly cooling the end of the plastic optical fiber while the lens-forming mold is pressed against the tip of the end of the plastic optical fiber or after the lens-forming mold is removed from the end of the plastic optical fiber (see, for example, Patent Document 1). Also proposed is a light guide having a spherical recess on its end face (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-75935 [Patent Document 2] Japanese Patent Application Publication No. 10-160940 Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Documents 1 and 2, by forming a lens or a concave surface at the tip of an optical fiber, it is possible to brightly illuminate the area around the light-emitting end of the optical fiber, but there is a problem in that the irradiation range and irradiation uniformity are insufficient because the direction of light emission varies depending on the shape and the refractive index of the core.

[0006] SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide an optical fiber that can achieve both a wide irradiation range and high irradiation uniformity. [Means for solving the problem]

[0007] In order to solve the above problems, the plastic optical fiber having a convex surface at the tip of the present invention comprises: 1) Among the irradiation angles θ, which are the angles between the light beams emitted from the optical fiber and the central axis of the optical fiber, the irradiation angle θmax of the most widely spread light beam is 60 degrees or more; 2) When the irradiation angle θ of the optical fiber is in the range of 0 degrees to 50 degrees, the luminance L1 at any measurement distance from the tip of the optical fiber is (L1>Lmax×0.8) relative to the maximum luminance Lmax in the entire irradiation range of the optical fiber at the measurement distance, 3) The luminance L2 at the measurement distance when the irradiation angle θ of the optical fiber is 60 degrees is (L2>Lmax×0.4) relative to the maximum luminance Lmax.

[0008] In such a plastic optical fiber according to the present invention, it is particularly preferable that the convex surface at the tip of the optical fiber is in the shape of a truncated cone, and that the upper surface of the truncated cone has a concave shape. [Effects of the Invention]

[0009] According to the plastic optical fiber of the present invention, the light incident on the optical fiber is emitted at a wide angle, and the illuminance of the irradiated light is uniform, so that the object to be observed can be uniformly illuminated over a wide observation range, which is advantageous in endoscopic surgery and ophthalmic surgery. [Brief explanation of the drawings]

[0010] [Figure 1] 1A is a schematic cross-sectional view of an optical fiber according to one embodiment of the present invention, and FIG. 1B is an enlarged cross-sectional view of the tip portion thereof. [Figure 2] 1A is a schematic diagram of the optical path when there is no recess at the tip of the optical fiber of the present invention, and FIG. 1B is an enlarged schematic diagram of the optical path at the tip of the optical fiber. [Figure 3] 1A is a schematic diagram of the optical path when the optical fiber of the present invention has a recess at the tip, and FIG. 1B is an enlarged schematic diagram of the optical path at the tip of the optical fiber. [Figure 4] 1 is a diagram for schematically explaining a measurement method 20 for evaluating the optical characteristics of an optical fiber of the present invention. [Figure 5] 2A to 2C are diagrams for schematically explaining the luminance distribution obtained by a method 20 for measuring the optical properties of the optical fiber of the present invention in the states (A) to (C). [Figure 6] 1A is a diagram for explaining a luminance distribution in an example of the optical characteristics of an optical fiber of the present invention, and FIG. 1B is a light distribution diagram expressing the same. [Figure 7] 1A is a schematic cross-sectional view showing an example of the tip shape of an optical fiber of the present invention, and FIG. 1B is an enlarged cross-sectional view of the tip portion of the optical fiber. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the optical fiber according to the present invention will be specifically described below, but the present invention is not limited to the following embodiments and can be modified in various ways depending on the purpose and application.

[0012] The optical fiber of the present invention has a core and at least one cladding layer. Light incident on the optical fiber travels through the core while undergoing total internal reflection at the core / cladding interface.

[0013] Examples of materials that can form the core of the optical fiber of the present invention include plastics. Examples of plastics include polymethyl methacrylate (PMMA), polymers containing methyl methacrylate as a polymerization component (e.g., copolymers of (meth)acrylic acid esters, (meth)acrylic acid, substituted styrenes, N-substituted maleimides, etc.), modified polymers obtained by polymer reaction of these with glutaric anhydride, glutarimide, etc., polystyrene, polycarbonate, polyethylene terephthalate, cycloolefins, etc. Two or more of these may be used. Among these, PMMA is preferred from the viewpoints of productivity, light transmittance, and environmental resistance. Here, in the present invention, PMMA refers to a (co)polymer containing 50 mol % or more of methyl methacrylate among the monomers that constitute the polymer. Preferably, the monomers that constitute the polymer contain 70 mol % or more, and more preferably 90 mol % or more, of methyl methacrylate.

[0014] When the core is PMMA, the polymer forming the cladding is preferably a vinylidene fluoride / tetrafluoroethylene copolymer, more preferably a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer. Such a copolymer has excellent adhesion to the core formed from PMMA, transparency, and flexibility, and can reduce light loss in a bending state. When the optical fiber has two or more cladding layers, it is preferable that the innermost cladding layer located on the core side is formed from such a polymer. Here, the innermost cladding layer refers to the cladding layer when there is only one cladding layer, or when the cladding is formed from multiple layers, refers to the cladding located innermost among them.

[0015] The optical fiber of the present invention has a convex surface at the output end face. By having a convex surface, the range of light emitted from the end face can be widened. Furthermore, the optical fiber of the present invention preferably further has a concave portion at the tip of the convex surface. By having a concave portion, it is possible to adjust the uniformity of brightness within the irradiation range, which is difficult to control with only a convex surface.

[0016] The optical fiber having a convex tip of the present invention is described with reference to the drawings. The optical fiber of the present invention has the following characteristics: (1) among the irradiation angles θ, which are the angles between the light beams emitted from the optical fiber and the central axis of the optical fiber, the irradiation angle θmax of the most widely divergent light beam is 60 degrees or more; 2) when the irradiation angle θ of the optical fiber is in the range of 0 to 50 degrees, the luminance L1 at any measurement distance from the tip of the optical fiber satisfies (L1 > Lmax × 0.8) with respect to the maximum luminance Lmax over the entire irradiation range of the optical fiber at that measurement distance; and 3) when the irradiation angle θ of the optical fiber is 60 degrees, the luminance L2 at the measurement distance satisfies (L2 > Lmax × 0.4) with respect to the maximum luminance Lmax.

[0017] The present invention will be described by way of examples with reference to Figures 1 to 3. However, the present invention should not be construed as being limited to these specific examples.

[0018] FIG. 1 is a schematic cross-sectional view of an optical fiber 10 having a convex tip according to one embodiment of the present invention. As shown in FIG. 1, the optical fiber 10 has a convex tip, where the tip portion of an optical fiber 11 having a flat tip surface is processed into a convex truncated cone shape to form a tip portion 16. Furthermore, a concave recess 18 is formed on an upper surface 17 of the truncated cone shape of the tip portion 16. The optical characteristics of the optical fiber 10 can be easily changed by changing the tip portion 16 and the recess 18 according to the desired optical characteristics. Although the shape of the convex surface of the tip portion 16 can be a spherical or ellipsoidal shape, a conical shape is particularly preferred in order to emit light at a wide angle and achieve more uniform illuminance of the irradiated light. Furthermore, a truncated cone shape is particularly preferred in order to realize a preferred form having a recess at the tip of the convex surface, which will be described later.

[0019] 2 and 3 are schematic diagrams of the optical path of the optical fiber 10 of the present invention. FIG. 2 shows the light output state when there is no recess at the tip of the convex surface. FIG. 3 shows the light output state when there is a recess 18 at the tip of the convex surface. As shown in FIG. 2, light incident on the optical fiber 10 travels through the core 11a while undergoing total reflection at the core 11a / clad 12 interface. Generally, the refractive index of the core is greater than the refractive index of air. Therefore, light output from the inclined tip of an optical fiber having a convex surface is totally reflected internally by the inclined surface of the truncated cone. As a result, the light is diffused and travels in a direction more perpendicular to the longitudinal direction of the optical fiber than the direction of travel of the light inside the optical fiber. However, since the top surface 17 of the truncated cone does not have a slope, the light output from the top surface of the truncated cone is bent by the difference in refractive index between air and the core before it is output. In other words, light rays approximately parallel to the central axis of the optical fiber travel straight and are output, which tends to result in extremely high brightness near the extension of the central axis of the optical fiber.

[0020] 3, the light emitted from the upper surface 17 of the truncated cone of the tip 16 is bent by the recess 18 formed on the upper surface 17, thereby changing the trajectory of the light ray emitted from the upper surface 17. This alleviates the phenomenon of extremely high brightness in the vicinity of the extension of the central axis of the optical fiber, which occurs when there is no recess, and makes the illumination uniform. From this point of view, it is preferable that the recess 18 is provided in the region of the upper surface 17 of the truncated cone that includes the central axis of the optical fiber.

[0021] An example of the optical characteristics of an optical fiber 10 having a convex surface at its tip will be described with reference to Figures 4 to 6. Figure 4 is a diagram schematically illustrating a measurement method 20 for evaluating the optical characteristics of an optical fiber of the present invention. As shown in Figure 4, light emitted from the optical fiber 10 is irradiated onto a reflector 21 installed at a position opposite the optical fiber 10. The intensity of the light reflected by the reflector 21 can be measured with a luminance measuring device to measure the light intensity at each irradiation angle θ. In this case, the irradiation distance D is the distance between the tip of the optical fiber 10 and the reflector 21, and the radius of the light projected onto the reflector 21 is R. By measuring the size of this radius R, the irradiation angle θ, which is the angle between the central axis of the optical fiber 10 and the emitted light ray, can be calculated as θ = ARCTAN(R / D).

[0022] Here, there is no particular upper limit to the irradiation distance D, and it may be set at a distance that allows the light emitted from the optical fiber 10 to sufficiently reach the reflector 21, taking into consideration the intensity of the light incident on the optical fiber 10. There is also no particular lower limit to the distance, but if the measurement is made at too close a distance, the irradiation radius R of the light projected onto the reflector 21 becomes small, which may result in a large measurement error when calculating the irradiation angle θ, making it impossible to accurately evaluate the optical characteristics. Therefore, the inventors set the irradiation distance D to be at least five times the diameter of the optical fiber 10 to be measured, and evaluated the optical characteristics.

[0023] FIG. 5 is a diagram illustrating a luminance distribution obtained by a method 20 for measuring optical characteristics. FIG. 5(A) is a diagram illustrating the entire irradiation range 22 of light emitted from an optical fiber, the maximum luminance Lmax, and the maximum irradiation angle θmax. As shown in FIG. 5(A), light emitted from the optical fiber toward the opposing reflector 21 is projected onto the reflector 21 in an approximately circular shape with a radius R. The shaded area indicates the entire irradiation range 22 of light irradiated onto the reflector 21, and the black square indicates the virtual intersection between the extension of the central axis of the optical fiber and the reflector, i.e., the θ=0° position 23. The position on the circumference of the radius R indicates the θ=θmax position, and the black square indicates the maximum luminance Lmax position 24, which is the maximum luminance within the entire irradiation range 22.

[0024] Fig. 5(B) is a diagram illustrating luminance L1 when the irradiation angle θ is in the range of 0° to 50°. As shown in Fig. 5(B), irradiation range 25 when θ=0° to 50° corresponds to a substantially circular portion of radius R1 within the entire irradiation range 22 of radius R. The luminance at any position within this irradiation range 25 is L1.

[0025] Fig. 5(C) is a diagram illustrating the luminance L2 at a position where the irradiation angle θ is 60°. As shown in Fig. 5(C), the position where the irradiation angle θ is 60° corresponds to the approximately circular portion 26 of radius R2 within the entire irradiation range 22 of radius R. In other words, any luminance on the circumference of the approximately circular portion 26 is the luminance L2 at a position where the irradiation angle θ is 60°.

[0026] Here, the optical characteristics of the optical fiber of the present invention will be described with reference to Fig. 6. Fig. 6 is a diagram illustrating an example of the optical characteristics of the optical fiber of the present invention. Fig. 6(A) is a diagram illustrating a method for graphing the luminance distribution obtained by measurement method 20. As shown in Fig. 6(A), in the luminance distribution obtained by measurement method 20, by graphing the luminance on chord 27 passing through the center of a circle of radius R, i.e., position 23 at θ=0°, the luminance distribution in the irradiation range of θ=0° to θmax can be expressed as a light distribution diagram.

[0027] FIG. 6(B) is a light distribution diagram expressing the luminance distribution using the method shown in FIG. 6(A). As shown in FIG. 6(B), the optical characteristics of the optical fiber of the present invention can be shown in a light distribution diagram with the irradiation angle θ on the horizontal axis and the luminance L on the vertical axis. The magnitude of the luminance L varies depending on the irradiation distance D (shown in FIG. 4) between the tip of the optical fiber and the reflector 21, so it is used as an index for relatively comparing the luminance within the irradiation range. In FIG. 6(B), the luminance L is normalized with the maximum luminance Lmax over the entire irradiation range set to 1, and the magnitude of the luminance at each irradiation angle θ on the chord 27 is displayed. Furthermore, to ensure measurement stability, the maximum irradiation angle θmax is calculated by determining the radius R so that the irradiation range is at least 5% of the maximum luminance, cutting off less than 5% of the maximum luminance.

[0028] As shown in Figure 6(B), the optical characteristics of the optical fiber of the present invention are such that the irradiation angle θmax of the widest beam is 60 degrees or more. Furthermore, when the irradiation range is from 0 degrees to 50 degrees, the brightness L1 in that irradiation range is 80% or more of the maximum brightness Lmax. Furthermore, when the irradiation angle θ is 60 degrees, the brightness L2 is 40% or more of the maximum brightness Lmax. Such a light distribution ensures uniformity of illumination within the irradiation range while irradiating a wide range.

[0029] In addition, in FIG. 6(B), a light distribution diagram is shown for one chord 27 as an example of optical characteristics, but by drawing light distribution diagrams for all chords 27 of a circle of radius R in the entire irradiation range 22 shown in FIG. 6(A), it is possible to get an overview of the optical characteristics of the optical fiber 10 of the present invention.

[0030] Here, by setting the maximum irradiation angle θmax to 60 degrees or more, a wider range can be irradiated when irradiating an observation object with a single optical fiber. Furthermore, for example, when irradiating an observation object with two optical fibers, the respective irradiation ranges overlap, making it easy to irradiate the entire range to be imaged. If the maximum irradiation angle θmax is less than 60 degrees, the irradiation ranges of the two optical fibers may not overlap depending on the irradiation distance, resulting in some ranges that cannot be irradiated.

[0031] Regarding illumination uniformity, the luminance L1 in the illumination angle θ range of 0 to 50 degrees is equal to or greater than the maximum luminance Lmax × 0.8, and preferably equal to or greater than Lmax × 0.85. If L1 is smaller than Lmax × 0.8, the difference between light and dark will be large when illuminating the object to be observed, and the object may not be observed correctly.

[0032] The luminance L2 at a position where the irradiation angle θ is 60 degrees is equal to or greater than Lmax × 0.4, and preferably equal to or greater than Lmax × 0.5. If L2 is smaller than Lmax × 0.4, for example, when illuminating an observation object with two optical fibers, the overlapping light will be weak, causing a difference in brightness, which may prevent the observation object from being observed correctly.

[0033] An example of the tip portion 16 of the optical fiber 10 of the present invention will be described with reference to FIG. 7. FIG. 7(A) is a schematic cross-sectional view of the tip portion 16 of the optical fiber 10 of the present invention. Note that the following description is merely for the purpose of deepening understanding of the present invention through examples, and the present invention should not be construed as being limited to this specific embodiment. The tip portion 16 of the optical fiber 10 of the present invention shown in FIG. 7(A) has a truncated conical shape. The base angle α of the truncated cone is preferably in the range of 55 to 75 degrees, and more preferably in the range of 58 to 66 degrees. If the base angle α of the truncated cone is less than 55 degrees, the angle at which light is bent by the slope when emitted becomes small, so the irradiation angle θ does not increase, and the maximum irradiation angle θmax may be less than 60 degrees. Furthermore, if the base angle α of the truncated cone is greater than 75 degrees, the tip of the truncated cone becomes sharp, which may cause the tip shape to collapse or break, making the optical fiber difficult to handle.

[0034] 7(B), the top surface 17 of the truncated cone of the tip 16 of the present invention has a recess 18. By providing the recess 18, it is possible to reflect light at an irradiation angle near θ=0 degrees out of the light rays irradiated from the top surface 17 of the truncated cone and emit it at a wide angle. If this light ray near θ=0 degrees is emitted directly from the top surface 17 of the truncated cone, the brightness near θ=0 degrees will be higher than the surrounding area, and the maximum brightness Lmax will peak near θ=0 degrees, which may impair the uniformity of illumination within the irradiation range.

[0035] The concave shape of the recess 18 is not particularly limited, but is preferably either a spherical shape, an ellipsoidal shape, or a cone shape. From the viewpoint of the ease of spreading the emitted light, a cone shape is more preferable. Furthermore, it does not need to be geometrically perfect, as long as it is similar to each shape. For example, the tip of the cone shape may be rounded due to the tool radius generated during machining.

[0036] The base angle α of the truncated cone of the tip portion 16 and the shape of the recess 18 in the present invention can be measured by cutting the optical fiber parallel to the drawing direction so that the central axis passes through it, and then observing it under magnification using a digital microscope. The magnification for the magnification observation is selected to be between 10 and 200 times, with the entire tip portion 16 included in the field of view and the base angle α being observable. For the truncated cone of the tip portion 16 of the optical fiber, the angle between the base and the inclined surface of the truncated cone can be taken as the base angle. The shape of the recess 18 can also be observed in a similar manner. The refractive index n can be measured using an Abbe refractometer in an atmosphere at room temperature (25°C).

[0037] The outer diameter of the optical fiber according to the embodiment of the present invention is preferably 0.1 to 1.5 mm. By setting the outer diameter of the optical fiber to 1.5 mm or less, flexibility can be improved. When used in an observation probe for an endoscope that can be inserted into the bile duct or pancreatic duct, taking into consideration the need to store the optical fiber together with the imaging element and treatment forceps, and the need to bend the observation probe 90 degrees when inserting it into the bile duct or pancreatic duct, the outer diameter of the optical fiber is more preferably 1.0 mm or less.

[0038] Methods for forming the tip portion 16 by end surface processing include, for example, a method of hot pressing using a mold, a method of cutting the end surface, and a method of joining a tip member. Among these, from the viewpoint of forming the tip shape with high precision, a method of hot pressing using a mold and a method of joining a tip member are preferred. The shape of the mold and the conditions of hot pressing can be arbitrarily applied according to the core material and tip shape.

[0039] The optical fiber according to the embodiment of the present invention can be suitably used for applications such as wiring inside moving bodies such as automobiles, aircraft, ships, and trains, short-distance communication wiring for AV equipment, household appliances, office appliances, etc., medical endoscopic illumination, ophthalmic surgical illumination, catheter illumination, microscope illumination, light-guiding sensors for robots, photoelectric sensors for industrial equipment, automobile collision sensors, decorative wall illumination, and indoor illumination. It is particularly suitable for applications requiring a wide illumination range, such as endoscopic illumination, ophthalmic surgical illumination, and catheter applications. That is, it can be suitably used in endoscopic illumination devices having the above-described optical fiber, ophthalmic surgical illumination probes having the above-described optical fiber as ophthalmic surgical illumination, and vascular catheters having the above-described optical fiber as catheter illumination or an optical sensor.

[0040] An endoscopic illumination device according to an embodiment of the present invention has the above-described optical fiber and can be used in combination with an endoscope. An ophthalmic surgical illumination probe according to an embodiment of the present invention has the above-described optical fiber as an illumination for ophthalmic surgery. A vascular catheter according to an embodiment of the present invention has the above-described optical fiber as an illumination for the catheter or an optical sensor.

[0041] In these lighting fixtures and lighting equipment, halogen lamps that are brighter than ordinary incandescent lamps, xenon lamps that are high in brightness and close to natural light, and LEDs as high-intensity light sources can be suitably used as light sources. [Example]

[0042] The present invention will be described in more detail below with reference to examples. The core materials and cladding materials used in each example and comparative example, and the optical fibers produced in each example and comparative example, were evaluated by the following methods.

[0043] Core diameter: Five randomly selected locations from the optical fibers produced in each Example and Comparative Example were cut perpendicular to the drawing direction, and the cross sections were polished so that the core / cladding interface could be observed. After that, they were subjected to magnified observation using a VHX-8000 digital microscope (Keyence Corporation). The magnification for magnified observation was between 10 and 200 times, and a range was selected so that the entire cross section was within the field of view and the interface could be observed. In the cross section, the diameter of the core of the optical fiber was measured as the fiber diameter. The core diameter was measured for each of the five cross sections, and the average value was taken as the core diameter.

[0044] Base angle of the truncated cone: The optical fibers produced in each example and comparative example were cut parallel to the drawing direction so that the central axis passed through them, and then magnified and observed using a digital microscope VHX-8000 (manufactured by Keyence Corporation). The magnification for magnification observation was between 10 and 200 times, and a range was selected so that the entire tip shape was within the field of view and the interface could be observed. The angle between the base and the inclined surface of the truncated cone was measured and used as the base angle.

[0045] Concave shape of the upper surface of the truncated cone: The optical fibers produced in each of the examples and comparative examples were cut parallel to the drawing direction so as to pass through the central axis, and were observed under magnification using a digital microscope VHX-8000 (manufactured by Keyence Corporation).

[0046] Refractive index of core: Measured at room temperature (25° C.) using an Abbe refractometer.

[0047] Maximum irradiation angle: Light was irradiated onto a reflector SRT-99-100 (manufactured by Labsphere) positioned 5 cm away (distance D) from the end face of the optical fiber produced in each example and comparative example, and the irradiation radius R was measured using a spectroradiometer SR-5000 (manufactured by Topcon Corporation), and θ was calculated as ARCTAN(R / D).

[0048] Luminance: The intensity of the light reflected from the reflector was measured over the entire irradiation range 22 using a spectroradiometer SR-5000 (manufactured by Topcon Corporation). The luminance at each irradiation position was extracted from the overall luminance distribution.

[0049] [Example 1] A vinylidene fluoride (2F) / tetrafluoroethylene (4F) copolymer (refractive index 1.41) was supplied to the composite spinning machine as the cladding material. Furthermore, PMMA (refractive index 1.49) produced by continuous axial polymerization was supplied to the composite spinning machine as the core material, and the core and cladding were melt-spun into a core-sheath composite at 240°C to obtain a bare fiber. The end faces of the obtained bare fiber were polished flat, and then the end faces were processed by joining a convex surface made by thermoforming.

[0050] The optical fiber thus obtained was evaluated by the above-mentioned evaluation method, and the results are shown in Table 1.

[0051] [Examples 2 to 5] Optical fibers were obtained in the same manner as in Example 1, except that the base angle α of the truncated cone and the shape of the recess 18 were changed as shown in Table 1. These optical fibers were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0052] All of the fibers satisfied the following conditions: 1) the irradiation angle θmax was 60 degrees or more, 2) L1>Lmax×0.8, and 3) L2>Lmax×0.4.

[0053] [Comparative Examples 1 to 5] Optical fibers were obtained in the same manner as in Example 1, except that the base angle α of the truncated cone and the shape of the recess 18 were changed as shown in Table 2. These optical fibers were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

[0054] None of the fibers satisfied at least one of the following: 1) the irradiation angle θmax was 60 degrees or more, 2) L1>Lmax×0.8, or 3) L2>Lmax×0.4.

[0055] [Table 1]

[0056] [Table 2] [Explanation of symbols]

[0057] 10: Optical fiber with a convex tip 11: Optical fiber 11a: Core 12: Clad 16:Tip 17: Top of the truncated cone 18: Recess 20:Measurement method 21:Reflector 22: Full illumination range 23: Irradiation angle 0 degrees 24: Maximum brightness position 25: Irradiation angle range of 0 to 50 degrees 26: 60 degree beam angle position 27: Strings α: base angle of the truncated cone θ: Irradiation angle θmax: Maximum irradiation angle D: Beam distance L: Brightness L1: Brightness at an irradiation angle of 0 to 50 degrees L2: Luminance at an irradiation angle of 60 degrees Lmax: Maximum brightness within the illumination range R: Radius of irradiation

Claims

1. A plastic optical fiber having a convex surface at the tip, 1) Among the irradiation angles θ, which are the angles between the light beams emitted from the optical fiber and the central axis of the optical fiber, the irradiation angle θmax of the most widely spread light beam is 60 degrees or more; 2) When the irradiation angle θ of the optical fiber is in the range of 0 degrees to 50 degrees, the luminance L1 at any measurement distance from the tip of the optical fiber is (L1>Lmax×0.8) relative to the maximum luminance Lmax in the entire irradiation range of the optical fiber at the measurement distance, 3) The luminance L2 at the measurement distance when the irradiation angle θ of the optical fiber is 60 degrees satisfies (L2>Lmax×0.4) with respect to the maximum luminance Lmax. A plastic optical fiber having a convex surface at its tip.

2. 2. The plastic optical fiber according to claim 1, wherein the convex surface of the tip of the optical fiber is in the shape of a truncated cone, and the upper surface of the truncated cone has a concave shape.

3. 3. The plastic optical fiber according to claim 2, wherein the base angle of the truncated cone is between 55 degrees and 75 degrees.

4. 3. The plastic optical fiber according to claim 2, wherein the concave shape is a spherical shape, an ellipsoidal shape, or a conical shape.

5. An endoscope illumination device comprising the plastic optical fiber according to any one of claims 1 to 4.

6. 5. An ophthalmic surgical illumination probe having the plastic optical fiber according to claim 1 as illumination for ophthalmic surgery.

7. A blood vessel catheter having the plastic optical fiber according to any one of claims 1 to 4 as a catheter illumination or optical sensor.

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