JP2021196604A - Optical fiber - Google Patents

Abstract

To provide an optical fiber having excellent uniformity in radiation.SOLUTION: An optical fiber includes a core and at least one layer of a cladding, the optical fiber having an emission end face of a protruded shape, in which a flatness ratio E of the protruded part, a numerical aperture X of the optical fiber, and a refractive index N of the core satisfy a relation of -1.3≤E×X/N≤0.5.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical fiber, an endoscope lighting device using the optical fiber, a probe for subocular surgical lighting, and a vascular catheter.

In endoscopic surgery and ophthalmic surgery, a method is generally adopted in which light is incident from one end of an optical fiber and light is irradiated from the exit end surface to observe the affected area. The larger the light irradiation angle, the wider the area around the affected area can be observed. Therefore, an optical fiber having a large numerical aperture is preferably used. In order to further widen the irradiation range of light, it is effective to install a lens near the emission end face or to process the end face by heating or cutting. However, lenses are generally expensive, and their use complicates the design. Therefore, end face processing, which is easy to process easily, is preferably used.

As a method for forming a lens on the end face of the optical fiber, (a) a step of preparing a plastic optical fiber having an exposed end portion of a predetermined length, and (b) forming a heated lens at the tip of the end portion of the plastic optical fiber. A heating step in which a mold is pressed to soften or melt a part or the whole of the end portion to form the tip of the end portion into a lens shape, and (c) for forming a lens on the tip of the end portion of a plastic optical fiber. It comprises a rapid cooling step of forcibly cooling the end of the plastic optical fiber while the mold is pressed or after the lens forming mold is separated from the end of the plastic optical fiber. A plastic optical fiber end face processing method (see, for example, Patent Document 1) has been proposed. Further, it is an optical fiber having a base end portion for introducing light from a light source and a tip light emitting portion for radiating the introduced light, and the tip surface of the tip light emitting portion forms a curved uneven surface, and the bending surface is formed. There has been proposed a light irradiation optical fiber (see, for example, Patent Document 2) in which the introduced light is radiated radially through the uneven surface.

Japanese Unexamined Patent Publication No. 8-75935 International Publication No. 2015/133119

As described in Patent Documents 1 and 2, by forming a lens or an uneven surface at the tip of the fiber, it is possible to brightly illuminate the periphery of the light emitting end of the fiber, but the shape, the refractive index of the core, and the fiber Since the light emission direction differs depending on the numerical aperture and the like, there is a problem that the irradiation uniformity is insufficient.

Therefore, a main object of the present invention is to provide an optical fiber having excellent irradiation uniformity.

The present invention is an optical fiber having a core and at least one layer of clad, and the emission end face has a convex shape, the eccentricity E of the convex portion, the numerical aperture X of the optical fiber, and the refractive index N of the core. Is an optical fiber that satisfies the relationship of −1.3 ≦ E × X / N ≦ 0.5.

According to the present invention, it is possible to provide an optical fiber having excellent irradiation uniformity.

It is sectional drawing of the optical fiber which concerns on embodiment of this invention. It is a schematic diagram which shows the flatness in the optical fiber which concerns on embodiment of this invention. It is a schematic diagram which shows an example of the flatness in an optical fiber and the traveling direction of an emitted light. It is a schematic diagram which shows another example of the flatness in an optical fiber and the traveling direction of an emitted light.

Hereinafter, preferred embodiments of the optical fiber according to the present invention will be specifically described, but the present invention is not limited to the following embodiments, and the present invention is variously modified according to an object and an application. can do.

The optical fiber according to the embodiment of the present invention has a core and at least one layer of clad.
Examples of the material forming the core of the optical fiber according to the embodiment of the present invention include plastic and glass.
Examples of the glass include quartz glass, fluoride glass, chalcogenide glass, borate glass, phosphate glass, germanate glass, silicate glass and the like. Two or more of these may be used.

Examples of the multi-component glass include SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ system, SiO ₂ , ZnO, PbO system, and the like. The refractive index can be adjusted by adjusting the ratio of these components.
As the plastic, for example, polymethylmethacrylate (PMMA), a polymer containing methylmethacrylate as a polymerization component (for example, (meth) acrylic acid ester, (meth) acrylic acid, substituted styrene, N-substituted maleimide, etc. were copolymerized. Things), glutaric acid anhydride obtained by polymerizing them, modified polymers such as glutarimide, polystyrene, polycarbonate, polyethylene terephthalate, cycloolefin and the like. Two or more of these may be used. Among these, a (co) polymer containing methyl methacrylate as a main component is preferable from the viewpoints of productivity, translucency, environmental resistance and the like. Here, "mainly composed" means that it occupies 50 mol% or more of the monomers constituting the polymer. The monomer constituting the polymer preferably contains 70 mol% or more of methyl methacrylate, and more preferably 90 mol% or more.

The core may further contain a stabilizer such as an antioxidant and other additives in a small amount as long as it does not affect the translucency.
The optical fiber according to the embodiment of the present invention has at least one layer of cladding. It may have two or more layers of cladding.

When the core is PMMA, the polymer forming the clad is preferably vinylidene fluoride / tetrafluoroethylene copolymer, and more preferably vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer. Further, vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer is more preferable. Such a copolymer is excellent in adhesion to a core formed from PMMA, transparency and flexibility, and can reduce light loss in a bent state. When the clad has two or more layers, it is preferable that the innermost clad located on the core side is formed from such a polymer. Here, the clad of the innermost layer refers to the clad when it has one clad, and refers to the clad located on the innermost side when the clad is formed of a plurality of layers.

In the optical fiber according to the embodiment of the present invention, the glass transition temperature of the innermost clad is preferably −60 to 95 ° C. When the glass transition temperature is −60 ° C. or higher, the clad has flexibility, so that end face processing is easy. When the glass transition temperature is 95 ° C. or lower, cracks are less likely to occur in the clad, end face processing is easy, and irradiation uniformity can be further improved. More preferably, it is −50 to 50 ° C. Even more preferably, it is -20 to 20 ° C. Here, the "glass transition temperature of the clad" means the glass transition temperature of the component constituting the clad, and is described in JIS K 7121-1987 using a differential scanning calorimeter (DSC). The temperature rise rate: can be measured under the condition of 10 ° C./min.

The optical fiber according to the embodiment of the present invention has a convex shape at the emission end face. Examples of the convex shape include a lens shape having a curved surface, a conical shape having a top, and the like. By having a convex shape, the uniformity of irradiation of light from the end face can be improved.

FIG. 1 shows a schematic cross-sectional view of an optical fiber according to an embodiment of the present invention. The upper figure of FIG. 1 shows an example of the case where the convex shape is a lens shape, and the lower figure shows an example of the case where the convex shape is a conical shape. The optical fiber has a portion (A) having a constant fiber diameter and a convex portion (C) having a convex shape, and the convex portion (C) is from a portion (B) where the fiber diameter becomes smaller to the tip of an end face. Refers to the part of.

FIG. 2 shows a schematic diagram showing the flatness of the optical fiber according to the embodiment of the present invention. The flatness E is calculated by E = 1- (b / a) from the radius a at the portion (B) where the fiber diameter becomes small and the distance b in the optical fiber longitudinal direction of the convex portion (C). That is, when the radius a is the same, the larger the distance b, the smaller the flattening E.

FIGS. 3 to 4 show a schematic diagram showing an example of the flatness of the optical fiber and the traveling direction of the emitted light. In the figure, (1) to (5) are (1) flattening E = 1, (2) flattening E = 0.75, (3) flattening E = 0.5, and (4) flattening =, respectively. 0, (5) Represents a convex shape with a flattening E = -1. In general, since the refractive index of the core is larger than the refractive index of air, the light emitted from the end face of the optical fiber is light when the flatness is positive, as compared with the traveling direction of the light inside the optical fiber. It travels more perpendicular to the longitudinal direction of the fiber. On the other hand, when the flatness is negative, the light travels in a direction more parallel to the longitudinal direction of the optical fiber than the traveling direction of the light inside the optical fiber. The larger the absolute value of the flattening, the greater the degree of polarization of the emitted light. With respect to FIG. 3, FIG. 4 is a schematic view when the numerical aperture of the optical fiber is large, and compared to FIG. 3, the emitted light travels in a direction more perpendicular to the longitudinal direction of the optical fiber. Here, the numerical aperture can be calculated from the refractive index of the core and the refractive index of the clad by the numerical aperture = ((refractive index of the core) ^2- (refractive index of the clad) ² ) ^1/2.

As described above, the present inventors proceed in a direction more perpendicular to the longitudinal direction of the optical fiber as the flatness E becomes larger, and the light emitted from the end face of the optical fiber travels in a direction more perpendicular to the longitudinal direction of the optical fiber, and the numerical aperture X becomes larger. It has been found that the light travels in a direction more perpendicular to the longitudinal direction of the optical fiber, and that the greater the refractive index N of the core, the greater the flexibility of light at the end face. As a result of diligent examination of these relationships, the flatness E of the convex portion, the numerical aperture X of the optical fiber, and the refractive index N of the core are −1.3 ≦ E × X / N ≦ 0.5. It has been found that irradiation uniformity is improved when the relationship is satisfied. When the value of E × X / N is smaller than −1.3, the light emitted from the end face travels in a direction more parallel to the longitudinal direction of the optical fiber and is difficult to travel in the vertical direction. Irradiation uniformity is reduced. The value of E × X / N is more preferably −1.2 or higher, and even more preferably −1.1 or higher. On the other hand, when the value of E × X / N is larger than 0.5, the reflection on the end face becomes large, and the light emitted from the end face travels in the direction more perpendicular to the longitudinal direction of the optical fiber and is parallel. Since it is difficult to proceed in the direction, the irradiation uniformity is reduced.

The numerical aperture of the optical fiber according to the embodiment of the present invention is preferably 0.40 or more. When the numerical aperture is 0.40 or more, the irradiation range can be widened and the irradiation uniformity can be further improved. The numerical aperture is more preferably 0.45 or more.

The outer diameter of the optical fiber according to the embodiment of the present invention is preferably 0.1 to 3.0 mm. From the viewpoint of improving flexibility, the outer diameter of the optical fiber is more preferably 1.5 mm or less. When used for an endoscope observation probe that can be inserted into the bile duct or pancreatic duct, it is necessary to store the optical fiber together with the imaging element and treatment forceps, and the observation probe needs to be bent 90 degrees when it is inserted into the bile duct or pancreatic duct. Considering the property, the outer diameter of the optical fiber is more preferably 1.0 mm or less.

The ratio (B / A) ratio of the cross-sectional area B of the core to the cross-sectional area A of the fiber according to the embodiment of the present invention is preferably 50% or more, more preferably 70% or more from the viewpoint of increasing the amount of incident light. , 80% or more is more preferable.

The amount of eccentricity of the clad with respect to the core of the optical fiber according to the embodiment of the present invention is preferably 10 μm or less. When the amount of eccentricity is 10 μm or less, the convex portion can be neatly produced by polishing the end face. The amount of eccentricity is more preferably 7 μm or less, further preferably 5 μm or less. Here, the amount of eccentricity is an index showing the deviation between the center of the core and the center of the virtual circle formed from the clad, and is the difference in the thickness of the upper and lower clad 2 in the cross section perpendicular to the longitudinal direction of the optical fiber. It can be calculated by the absolute value of the square root of the value obtained by adding the square of the square of the difference between the left and right clad thicknesses.

The optical fiber according to the embodiment of the present invention can be obtained, for example, by melt-spinning a material forming a core and a clad and then processing the end face into a convex shape.

Examples of the method of forming a convex shape by end face processing include a method of hot pressing using a die, a method of cutting an end face into a convex shape, and the like. Among these, a method of cutting the end face into a convex shape is preferable from the viewpoint of forming a convex shape with high accuracy. For cutting the end face, a cutting single-edged blade can be arbitrarily selected and used according to the material and shape.

The cutting blade is formed by cutting the end face of an optical fiber into a predetermined shape, and the shape of the cutting edge thereof is determined according to the shape of the end face of the optical fiber to be formed. For example, when the end face of the optical fiber is formed into a convex hemisphere (lens), the shape of the cutting edge of the cutting blade is a concave semicircle. In addition, when forming the end face of an optical fiber into a conical shape, a single-edged blade is prepared that cuts the end face of the optical fiber diagonally. , A structure such as cutting the tip of an optical fiber into a conical shape can be considered (for example, the same mechanism as that used for sharpening a pencil).

Further, the breaking elongation of the clad is preferably in the range of 100 to 800%. When it is 100% or more, the elongation of the optical fiber increases, it becomes difficult to break, and the workability is improved. If it is within 800%, the clad does not easily stretch during cutting, so that it is easy to cut and cutting chips are hard to be generated. More preferably, it is 300 to 650%.

The optical fiber according to the embodiment of the present invention includes wiring in a moving body such as an automobile, an aircraft, a ship, and a train, wiring for short-distance communication such as AV equipment, home equipment, and office equipment, and medical endoscope lighting. It can be suitably used for applications such as catheter lighting, microscope lighting, light guide sensor for robots, photoelectric sensor for industrial equipment, automobile collision sensor, wall decoration lighting, and interior lighting. In particular, it is suitable for endoscopic applications, ophthalmic surgery applications, and catheter applications where uniform irradiation is required. That is, an endoscope lighting device having the above-mentioned optical fiber, an ophthalmologic surgery lighting probe having the above-mentioned optical fiber as lighting for ophthalmic surgery, and a vascular catheter having the above-mentioned optical fiber as a catheter lighting or an optical sensor. It can be suitably used for such purposes.

In these lightings and lighting devices, as a light source, a halogen lamp brighter than a general incandescent lamp, a xenon lamp having high brightness and close to natural light, and an LED as a high brightness light source can be preferably used.

Hereinafter, the present invention will be described in more detail with reference to Examples. The core material and clad material used in each Example and Comparative Example and the optical fiber produced by each Example and Comparative Example were evaluated by the following methods.
Composition ratio of clad material: Obtained using solid 19F-NMR (AVANCE NEO 400 manufactured by Bruker).

Refractive index of core and clad: Measured in an atmosphere at room temperature of 25 ° C. using an Abbe refractive index meter.

Clad glass transition temperature (Tg): Using a differential thermal analyzer (DSC-50 manufactured by Shimadzu Corporation), the amount of heat generated while raising the temperature under the condition of a nitrogen stream and a heating rate of 20 ° C / min. The measurement was performed, and the tangent line between the baseline and the heat change point was defined as the glass transition temperature.

Amount of eccentricity of the clad with respect to the core: After polishing the cross section perpendicular to the longitudinal direction of the optical fiber, magnified observation was performed using a microscope, and the thickness of the clad was measured at four points on the top, bottom, left and right. The absolute value of the square root of the value obtained by adding the square of the difference between the upper and lower thicknesses and the square of the difference between the left and right thicknesses was obtained.
Irradiation uniformity: Light was irradiated to a position 2 cm away from the end face of the optical fiber, and visually evaluated based on the following criteria. If it is 3 or more, it can be practically used.
5: It emits light uniformly.
4: It emits light almost uniformly.
3: Light is emitted almost uniformly.
2: Light emission unevenness is observed in some parts.
1: Light emission unevenness is observed as a whole.

Fracture elongation of the clad: A sample compliant with ASTM D638 was prepared with the clad alone, and the sample was prepared by the method of ASTM D638. The test speed was 5 mm / min.

The abbreviations of the monomers used in this example are as follows.
PMMA: Polymethylmethacrylate
2F: Vinylidene fluoride
4F: Tetrafluoroethylene
6F: Hexafluoropropylene
MMA: Methyl Methacrylate
4FM: Tetrafluoropropyl methacrylate
5FM: Pentafluoropropyl methacrylate
8FM: Octafluoropentyl methacrylate
PS: Polystyrene.

[Example 1]
As a clad material, a vinylidene (2F) / tetrafluoroethylene (4F) copolymer having a copolymerization ratio shown in Table 1 (refractive index 1.41) was supplied to the composite spinning machine. Further, PMMA (refractive index 1.49, weight molecular weight 78,000) produced by continuous soul-like polymerization is supplied to a composite spinning machine as a core material, and the core and clad are core-sheath composite melt-spun at 240 ° C. , A bare fiber having a fiber diameter of 1000 μm (core diameter of 980 μm and clad thickness of 10.0 μm) was obtained. The obtained bare fiber was subjected to end face processing to form a convex shape on the end face by cutting. The flattening was 0.9.
Table 1 shows the results of evaluation of the optical fiber thus obtained by the above evaluation method.

[Examples 2 to 5]
An optical fiber was obtained in the same manner as in Example 1 except that the flatness was changed as shown in Table 1. Table 1 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

[Examples 6 to 20]
Using the clad material shown in Tables 1 and 2, an optical fiber was obtained in the same manner as in Example 1 except that the flatness was changed as shown in Tables 1 and 2. The results of evaluating these optical fibers in the same manner as in Example 1 are shown in Tables 1 and 2.

[Examples 21 to 25]
The core material multicomponent glass _(SiO 2: 34 _wt%, B _{2 O} 3: 5 wt%, _Na 2 O: 4 wt%, CaO: 8 wt%, BaO: 33 wt%, ZnO: 12 wt%, ZrO ₂ : 4% by mass) was changed, and an optical fiber was obtained in the same manner as in Example 1 except that the flatness was changed as shown in Table 2. Table 2 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

[Examples 26 to 30]
An optical fiber was obtained in the same manner as in Examples 1 to 5, except that the convex shape was a cone. Table 3 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

[Example 31]
An optical fiber was obtained in the same manner as in Example 1 except that the amount of eccentricity was changed as shown in Table 3. Table 3 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

[Example 32]
An optical fiber was obtained in the same manner as in Example 1 except that the core was changed to polystyrene. Table 3 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

[Examples 33 to 37]
An optical fiber was obtained in the same manner as in Example 1 except that the clad was changed to the clad shown in Table 2. Table 3 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

[Comparative Examples 1 and 2]
An optical fiber was obtained in the same manner as in Example 1 except that a multi-component glass was used as the core material and the flatness was changed as shown in Table 3. Table 3 shows the results of evaluation of these optical fibers in the same manner as in Example 1.

(A) A portion having a constant fiber diameter (B) A portion where the fiber diameter becomes smaller (C) A convex portion having a convex shape a A radius at a portion where the fiber diameter becomes smaller (B) b The optical fiber length of the convex portion (C) Directional distance b
(1) Convex shape when flattening E = 1 (2) Convex shape when flattening E = 0.75 (3) Convex shape when flattening E = 0.5 (4) Flattening = 0 (5) Convex shape when flattening E = -1

Claims (10)

An optical fiber having a core and at least one layer of clad, the emission end surface has a convex shape, and the flatness E of the convex portion, the numerical aperture X of the optical fiber, and the refractive index N of the core are -1. An optical fiber that satisfies the relationship of 3 ≦ E × X / N ≦ 0.5. The optical fiber according to claim 1, wherein the glass transition temperature of the innermost clad is −60 to 95 ° C. The optical fiber according to claim 1 or 2, wherein the numerical aperture X is 0.40 or more. The optical fiber according to any one of claims 1 to 3, wherein the core contains polymethylmethacrylate. The optical fiber according to any one of claims 1 to 4, wherein the amount of eccentricity of the clad with respect to the core is 10 μm or less. The optical fiber according to any one of claims 1 to 5, wherein the breaking elongation of the clad is 100 to 800%. An endoscope lighting device having the optical fiber according to any one of claims 1 to 6. A probe for ophthalmic surgery lighting having the optical fiber according to any one of claims 1 to 6 as lighting for ophthalmic surgery. A vascular catheter having the optical fiber according to any one of claims 1 to 6 as a catheter illumination or an optical sensor. An in-vivo lighting device having the optical fiber according to any one of claims 1 to 6.

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