KR20030068188A - Side-Illumination Type Optical Fiber - Google Patents

Abstract

The present invention relates to a side-emitting optical fiber comprising a core and a cladding disposed around the core, the cladding comprising a transparent first layer in contact with the core and a light diffusing second formed around the first layer. A layer, the two layers being integrally molded.

Description

Side-emitting optical fiber {Side-Illumination Type Optical Fiber}

As is known in the art, discharge tubes such as fluorescent lamps emit visible light in specific wavelength ranges and are used for illumination purposes. When the discharge tube is a neon tube, it is mainly used for advertisement or decoration in the form of neon sign. The discharge tube emits light by application of voltage. The discharge tube generates heat together with light. When using discharge tubes, leakage and heat generation should be considered. Therefore, the discharge tube cannot be used, for example, for underwater lighting or display purposes.

In order to realize illumination or display underwater, a lighting apparatus has been recently proposed in which a light source is arranged remotely from a place where illumination or display is performed. Such lighting devices include a light source disposed remotely from an illumination or display position, and an illumination or display optical fiber disposed at or near the illumination or display position. In general, an optical fiber has a core having a core for transmitting light incident from one end of the optical fiber to the other end, and a cladding having a lower refractive index than the core around the core.

Among the optical fibers, side-emitting optical fibers that are capable of emitting light from the side portions are known. Referring to this side-emitting optical fiber with reference to Figure 4, the optical fiber 20, as disclosed in US Patent No. 4,422,719, core 21 made of acrylic resin and the like. children. It is flexible and has a cladding 22 formed of polytetrafluoroethylene, available from Teflon® from E.I. Dupont de Nemours and Company. The cladding 22 comprises 2-10% by weight of light diffusing particles, such as metal oxide particles (eg titanium dioxide particles), uniformly. In addition, Japanese Unexamined Patent Application Publication No. 1998-148725 discloses an optical fiber obtained by coextrusion of a molten fluoropolymer containing at least one light diffusion additive of 50 to 4000 ppm with a resin mixture for crosslinking. WO 98/08024 also discloses an optical fiber in which a semi-transparent cladding material comprising a pigment of white or other color is formed on the core surface by melt casting. The optical fiber may emit light through the cladding when transmitting light incident from one or both ends thereof into the fiber.

It is also known to include other light diffusing layers in the cladding layer. For example, Japanese Laid-Open Patent Publication No. 2000-131530 discloses dividing a cladding layer into two layers, a light diffusing layer containing light diffusing particles and a transparent layer containing no light diffusing particles formed thereon. These two layers are integrally formed by coextrusion. In this technique, the light diffusing layer is in direct contact with the core.

In the configuration obtained in Japanese Unexamined Patent Publication No. 2000-131530, the lateral luminance of the optical fiber, in particular, the luminance at a position close to the light source is effectively improved, but the luminance decreases as it leaves the light source. This is because the attenuation of the luminance increases as the distance from the light source increases. Therefore, the optical fiber disclosed in Japanese Unexamined Patent Application Publication No. 2000-131530 is not effectively used for an illumination device having a long optical fiber of 10 m or more in length when the optical fiber is used as a light emitter.

Summary of the Invention

According to the present invention, in order to solve the above-mentioned problems, in a side-emitting optical fiber (often abbreviated as an optical fiber) having a core and a cladding disposed around the core, the cladding is a transparent first layer in contact with the core. And a light diffusing second layer formed around the first layer, and two layers are formed integrally. In this invention, it is preferable that the thickness of a 1st layer is 50-300 micrometers. It is preferable that the diameter of a core is 5-30 mm. It is also preferable that the cladding has a two-layer structure formed by coextrusion of two materials for producing the first layer and the second layer.

The present invention relates to a side-emitting optical fiber. In particular, the invention relates to a side emitting optical fiber which emits light incident from at least one end in the longitudinal direction of the core through the cladding surrounding the core.

1 schematically shows a cross section of a side-emitting optical fiber of the present invention.

2 is a graph showing the side light emission test results of Examples and Comparative Examples. This figure shows the change in luminance with respect to distance from the light source.

Fig. 3 is a graph showing the side emission test results of Examples and Comparative Examples. This figure shows the change in luminance with respect to the measurement angle at a position 2 mm away from the light source.

4 is a schematic cross-sectional view of a side-emitting optical fiber of the prior art.

The long side emitting optical fiber having a length of 10 m or more can be obtained by covering an optical fiber having a transparent single layer cladding on the core with a light diffusing translucent resin layer, and can also brighten the light by improving the uniformity of the luminance in the longitudinal direction. . This is because the optical fiber including the core and the transparent single layer cladding covering the core is capable of transmitting light from one end to the other in the longitudinal direction without light leaking from the surface, i.e., the side of the cladding. This is because the light incident into the optical fiber can effectively transmit the total internal reflection at the interface between the relatively low refractive index cladding and the relatively high refractive index core.

On the other hand, if the core has a relatively large diameter, for example more than 3 mm in diameter, even though the cladding does not contain light diffusing particles, light in the optical fiber from the side is leaked out and faintly emits light in the longitudinal direction. . As the core diameter increases, this phenomenon occurs more because there is more light reaching the interface between the core and the cladding without satisfying the overall internal reflection condition. In addition, the adhesion between the cladding and the core may be very good transparent to the naked eye, but in microscopic view it is partially uneven, and this uneven portion becomes the light emitting point.

Light leakage generally has a relatively low angle with respect to the direction parallel to the cladding side, and there are many components emitted from the cladding side. Therefore, an optical fiber having a translucent light-diffusion resin layer on the cladding has sufficient uniformity in luminance across the longitudinal direction, but cannot be used as a long light-emitting body such as a neon tube due to its low luminous intensity due to light leakage.

Therefore, the light diffusion layer is more closely attached to the cladding surface to reduce the leakage of light having a relatively low angle with respect to the direction parallel to the cladding side, and to increase the leakage of light having a relatively high angle with respect to the direction parallel to the cladding side. need.

Some methods for adhering the light diffusing layer on the cladding surface are already known. For example, there is a method of covering an electric wire with a resin, comprising cooling and solidifying a molten resin mixture of a transparent polymer and white inorganic powder dispersed therein on the cladding layer surface of the optical fiber. Another method involves preparing a light diffusing resin tube and inserting an optical fiber therein.

However, all of these methods involve an additional step of coating the light diffusing layer on the cladding surface resulting in an increase in manufacturing costs.

In addition, since the light diffusing layer is separately formed and coated on the cladding surface, it is difficult to improve the adhesion between the cladding and the light diffusing layer. This frequently causes layer separation between the light diffusing layer and the cladding due to the bending action of the optical fiber, the temperature change, and the like. Once layer separation occurs, the luminance of the separated portion is reduced and some difference in the luminance of the optical fiber occurs. Therefore, the optical fiber does not work well as illumination light for illumination.

The inventors further studied the occurrence of layer separation between the optical fiber and the light diffusing layer and found that when the optical fiber has a larger core diameter, the layer separation is observed more frequently, especially at core diameters of 5 mm or more. The reason for this tendency is explained below.

In the case of glass fibers, the fibers can be twisted to absorb bending strain and bend the glass fibers without breaking. On the other hand, if the diameter of the glass article is larger than the diameter of the fiber, for example, the glass rod cannot bend at all and will break if too large bending force is applied to the glass rod. It is generally true that rod-shaped products with large diameters do not twist at all and do not absorb bending deformation for bending work. Thus, the layer separation between the cladding and the light diffusing layer works the same as in glass rods and often occurs when the optical fiber has a large diameter.

The present invention will be described with reference to representative embodiments. In the drawings appended here, like numbers refer to like parts or equivalent parts. In Fig. 1, an optical fiber 10 is shown as one embodiment of the present invention. The optical fiber 10 has a core 1 at its center and a cladding 2 surrounding the core 1.

The core is generally formed of a polymer. The core formed from the polymer can be obtained by polymerizing the polymerizable material. The core can receive light from the light source from the exposed one end or both ends without loss from the light source. The core has sufficient light transmittance and transmits light from one end to the other.

The light transmittance of the core is 80% or more. By “light transmittance” is meant herein the value measured using light of wavelength 550 nm with a spectrophotometer. The refractive index of the polymer for core is generally 1.4 to 1.7.

The core is preferably a solid core formed of a flexible polymer. The flexible polymer may preferably be an acrylic polymer, ethylene-vinyl acetate copolymer, vinyl acetate-vinyl chloride copolymer or mixtures thereof. The polymer of the core may preferably be crosslinked to improve water resistance.

The polymerizable material for the core may be an acrylic monomer mixture. The acrylic monomer mixture for preparing the core contains (1) a polymerizable acrylic monomer having no hydroxyl group in the molecule and (2) a polymerizable hydroxyl-containing acrylic monomer. As used herein, "acrylic monomer" includes monomers having an acrylic group or monomers having a methacryl group, or both. Preferably it is methacrylate, ie methacrylic acid ester. Methacrylate can control core Tg to an appropriate range easily, and can improve characteristics, such as water resistance and light transmittance effectively. Unless the technical effect of this invention is impaired, the polymeric material for cores may be the (meth) acrylic-type oligomer formed by making 2 or more types of monomers react. In addition to the monofunctional monomer, a crosslinkable monomer having two or more functional groups can also be used.

Examples of acrylic monomers having no hydroxyl group include methacrylates such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobutyl methacrylate, t- Butyl methacrylate, lauryl methacrylate, dodecyl methacrylate and stearyl methacrylate. An acrylate having no hydroxyl group can be used in addition to methacrylate, and may be used as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isoamyl acrylate, lauryl acrylate, ste Aryl acrylate, isooctyl acrylate, etc. are mentioned. Unsaturated acids such as acrylic acid or methacrylic acid can also be used as monomers.

Examples of hydroxyl-containing acrylic monomers include 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate Elate, 3-hydroxypropyl acrylate, diethylene glycol monomethacrylate, diethylene glycol monoacrylate, triethylene glycol monomethacrylate, triethylene glycol monoacrylate, etc. are mentioned.

Examples of the crosslinking agent for crosslinking the core polymer include polyfunctional monomers such as diallyl phthalate, triethylene glycol di (meth) acrylate and diethylene glycol bisallylcarbonate.

Preferred examples of the acrylic monomer mixture of the present invention are

(a) a mixture of 2-hydroxyethyl methacrylate, methyl methacrylate, n-butyl methacrylate and triethylene glycol di (meth) acrylate,

(b) a mixture of 2-hydroxyethyl methacrylate, n-butyl methacrylate and triethylene glycol di (meth) acrylate, and

(c) a mixture of 2-hydroxyethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, triethylene glycol di (meth) acrylate, and the like.

When crosslinking the core polymer using a crosslinking agent, the amount of the crosslinking agent may be preferably 0.01 to 5.0% by weight, more preferably 0.1 to 4.5% by weight relative to the total weight of the polymerizable material. Also, as long as the properties of the core are not impaired, the core may contain additives. Examples of the additives include plasticizers, surfactants, colorants, stabilizers against heat, oxidation, and ultraviolet rays.

Any component of the polymerizable material for making the core can be changed to meet properties such as flexibility, weather resistance, color resistance, water resistance, and the like. The length of the core is generally 50 to 100 m, but is not limited thereto. In order to exhibit the technical effect of the present invention, the core length is preferably 10 m or more, more preferably 15 m or more. The cross section in the radial direction of the core is usually almost circular or almost elliptical, but is not limited thereto.

The diameter of the core is usually 3 to 30 mm. If the core diameter is smaller than 3 mm, the light emitting surface for the observer to check light emission is too thin and small, which is not suitable for illumination. On the other hand, if the core diameter is larger than 30 mm, the attenuation of the luminance in the longitudinal direction becomes large and the uniformity of the luminance cannot be improved. In addition, if the core diameter is large, the flexibility of the optical fiber is lowered, and therefore, it cannot be molded into an illumination device including a fiber having a desired shape. Therefore, in order to exhibit the excellent performance as a light-emitting body, it is preferable that the diameter of a core is 6-27 mm, More preferably, it is 7-20 mm.

The cladding 2 is integrally molded with the first layer 3 and the second layer 4 as described above. Preferably, the cladding 2 is formed by a coextrusion process in which two or more layers for forming the cladding are melt extruded together to form a layer, which is cooled and solidified. This method effectively improves the adhesion between the layers but does not increase the number of cladding forming steps. Thus, the cladding of the present invention can be manufactured in the same manner as a conventional cladding with a single layer except that the cladding has a plurality of layers.

Materials for forming each cladding layer are not limited but generally are tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer, trifluoro Polymers such as ethylene-vinylidene fluoride copolymer, polymethylpentene, ethylene-vinyl acetate copolymer, vinyl acetate-vinyl chloride copolymer and the like. The first layer in contact with the core of the cladding has a lower refractive index than the core.

Unless the performance of the present invention is impaired, the cladding may contain some additives. Examples of the additives include plasticizers, surfactants, curing agents, fillers (such as white pigments), colorants (such as dyes), stabilizers and the like.

The second layer of light diffusivity can be formed from a material that typically contains a fluorine-containing polymer and light-diffusing particles dispersed in the fluorine-containing polymer. The amount of the light diffusing particles is usually 0.01 to 50% by weight, preferably 0.1 to 45% by weight, more preferably 1 to 40% by weight relative to the total weight of the second layer. An amount less than the lower limit cannot obtain sufficient luminance (e.g., 100 candela / m ² or more in the case of white light emission) required as a light emitter such as neon sign. An amount greater than 50% by weight cannot emit light with sufficient brightness over the longitudinal direction.

The light diffusing particles may be beads usually obtained from glass beads or other materials, and inorganic particles such as titanium dioxide or silicon dioxide. Specific examples of the particles include white inorganic particles having a refractive index in the range of 1.5 to 3.0. Preferred examples of the white inorganic particles include barium sulfate (refractive index = 1.5), magnesia (refractive index = 1.8) and titania (titanium dioxide; refractive index = 2.6).

The light-diffusion particles may be other than the above, so long as the technical effects of the present invention are not impaired. In addition to the light diffusing particles, a colorant such as a fluorescent dye may be contained in the cladding layer to change white light incident on the core into colored light for emission.

The transparency of the cladding first layer can be expressed in light transmittance, preferably greater than 60%, more preferably greater than 70% and most preferably greater than 90%. If the light transmittance of the cladding first layer is too small, the brightness of the optical fiber may be lowered.

The thickness of the cladding first layer is preferably 50 to 300 μm, more preferably 70 to 280 μm, most preferably 100 to 250 μm. If the thickness of the cladding first layer is too small, the luminance across the longitudinal direction is significantly attenuated and the uniformity of the luminance across the longitudinal direction cannot be improved. When the core diameter is 5 mm or more, the cladding first layer is preferably as thick as possible in order to improve the uniformity of luminance. If the thickness of the cladding first layer is too large, the luminance at the position away from the light incidence point is lowered, so that the uniformity of the luminance cannot be maintained. In both cases, optical fibers are not suitable as lighting emitters.

The thickness of the second layer of the cladding is not particularly limited and may be selected within a range in which the cladding does not become opaque. It is preferable that the thickness of a 2nd layer is 10 micrometers or more, and the thickness of the whole cladding is 2 mm or less.

The optical fiber of the present invention is produced by making a tubular cladding having a desired length, filling the polymerizable material therein and then polymerizing the material to form a polymerized core and a cladding covering the core. The detailed description regarding manufacture is mentioned later.

First, a cladding (ie cladding tube) is produced. Typically, the cladding is obtained by coextrusion, forming a cladding tube with the desired thickness, diameter and length. The cladding thus produced is wound on a feed roll. The cladding wound on the feed roll is wound on the take-up roll. The feed roll and the take-up roll are used in combination, and the longitudinally continuous cladding is transported from the feed roll into a heating zone (a vessel containing a heating medium, for example, a hot water container) disposed between the take-up rolls and the heating zone. Pass through.

The heating zone, ie the heating vessel, may have two openings through which the cladding passes. The two openings are the cladding inlet on the feed roll side and the cladding outlet on the take-up roll side. The heating vessel may be one having an opening facing upward in the vertical direction. The cladding is introduced into the container through the one opening and its direction is changed near the bottom of the container and transported out through the same opening. As described above, the cladding is immersed in the heating medium to terminate the polymerization reaction of the core and the optical fiber is discharged from the opening.

The polymerizable material is usually filled into the cladding tube under moderate pressure. In this method, material is fed into the cladding from one end and then the other end of the cladding is sealed. Sealing of the cladding may be accomplished by fitting a metal stopper or valve to one end of the cladding. Filling the polymeric material into the cladding tube can be accomplished by connecting an opening at one end of the cladding with the tank for the polymeric material and pressurizing the interior of the tank to continuously push the material into the cladding tube.

As described above, the polymerizable material in the cladding is heated in the heating zone to initiate and terminate the polymerization reaction to obtain an optical fiber having a core in close contact with the cladding layer.

Heating can be carried out at 35 to 90 ° C, preferably at 40 to 85 ° C. The time for the cladding to stay in the heating zone is not particularly limited, but is generally 10 minutes to 5 hours, preferably 15 minutes to 3 hours. The length of the cladding is preferably 10 m to 3,000 m, more preferably 20 m to 2,000 m.

The elastic modulus of the cladding is preferably 10 to 700 MPa, more preferably 20 to 600 MPa. The "elastic coefficient" of the cladding is the value at the heating temperature. The cladding preferably has a tube thickness of 0.01 to 2 mm, more preferably 0.05 to 1.5 mm, even more preferably 0.2 to 1 mm. If the thickness is too thin, the water resistance of the optical fiber may be degraded. Too thick a thickness may degrade flexibility. The inner diameter of the cladding can be measured by the core diameter of the final optical fiber.

The optical fiber of the present invention is suitably used as a long light emitter of a lighting device equipped with information display such as billboards, neon signs and road signs.

The optical fiber of the present invention emits light incident from one or both ends of the core to the outside through the side or circumferential surface of the cladding. The light source may be a high brightness lamp such as a xenon lamp, a halogen lamp, a flush lamp, or the like. Lamps typically consume between 10 and 500 W of power.

For example, an illumination device can be formed using the optical fiber of the present invention as an elongated light emitter as shown in FIG. In Fig. 5, the side light emitting portion 30 formed of the long optical fiber of the present invention shows a figure including some curves. In the lighting device of the present invention, the light-emitting body including such a figure constitutes all or part of an advertisement or guide information.

The light transmitting part 32 connecting the light source 31 and the side light emitting part 30 does not constitute the above information. Therefore, it is preferable to coat the light transmitting part 32 with a light shielding jacket (black soft vinyl chloride resin) so as not to emit light.

In the optical fiber of the present invention, no interlayer peeling occurs even by the bending operation. Therefore, it is very easy for an optical fiber to form a figure, a character, and a symbol including a curve as shown in Fig. 5, thus showing satisfactory performance as an illuminant for illumination.

In addition, when the optical fiber of the present invention is used as a long light emitter of the lighting apparatus, when light is incident from one end of the optical fiber by one light source, the length of the optical fiber is preferably 10 to 50 m, more preferably 15 to 40 m, and when light is incident from both ends by two light sources, the length of the optical fiber is 10 to 100 m, preferably 15 to 80 m.

<Example 1>

A cladding was prepared having a first layer and a second layer formed integrally.

Two extruders were used and the extruder of each extruder was connected with the coextrusion die. One extruder was charged with tetrafluoroethylene-hexafluoropropylene (FEP) resin FEP 100J manufactured by Mitsui Du Pont Chemical Co., Ltd. as a material for forming the first layer. In another extruder, as a material for forming the second layer, a mixture of 100 parts by weight of FEP 100J and 1 part by weight of NP 20 WH, which is FEP manufactured by Daikin Industries Co., Ltd., was charged. NP 20 WH resin contains 2.3 weight percent titanium dioxide. Thus, the second layer of this example contained about 2.3% by weight titanium dioxide (light diffusing particles). The light transmittance of the cladding first layer was 9.5%.

The cladding of the examples was prepared using an extruder as described above. The cladding is tubular and has openings at both ends. The first layer of cladding had a transparent resin layer of about 200 μm thick and the second layer had a light diffusion layer of about 450 μm thick. The outer diameter of the cladding was about 15 mm.

4 parts by weight of hydroxyethyl methacrylate, 80 parts by weight of n-butyl methacrylate, 16 parts by weight of 2-ethylhexyl methacrylate and 1 part by weight of triethylene glycol dimethacrylate as polymerizable materials for preparing the core From this a monomer mixture was prepared, to which lauroyl peroxide (polymerization initiator) was added.

The polymeric material was poured from the one end into the cladding and the other end was sealed. The sealed end of the cladding was passed through a heating zone to heat to polymerize the polymerizable material and transported in continuous contact with nitrogen gas from the other opening. The polymerized material formed a solid core to obtain a side emitting optical fiber.

<Example 2>

A side-emitting optical fiber was prepared as described generally in Example 1 except that the amount of NP 20 WH fed to the other extruder was changed from 1 part by weight to 20 parts by weight. The amount of light diffusing particles (titanium dioxide) contained in the cladding second layer of the obtained optical fiber was about 38.3 wt%.

Comparative Example 1

A side-emitting optical fiber was prepared as generally described in Example 1 except that no NP 20 WH was used and only FEP 100 J was used.

Comparative Example 2

As described generally in Example 1, except that the resin introduced into Extruder 1 was replaced with a mixture of 10: 1 by weight of FEP 100 J and NP 20 WH, and the resin introduced into Extruder 2 was only FEP 100 J. A light emitting optical fiber was prepared. In this experiment, the first layer had light diffusivity and the second layer was transparent. The light transmittance of the cladding second layer was 95%.

(1) Measurement of side light emission luminance

The side light emission luminance was measured as described below.

A halogenated metal lamp (LBM 130H manufactured by Sumitomo 3M Co .; power consumption 130W) was connected to one end of the core of the optical fiber. Luminance was measured using a luminance meter CS-100 manufactured by Minolta Co., Ltd. at a position away from the light source by emitting light. The luminance meter was placed at a position 60 cm from the side of the optical fiber. The angle formed between the normal of the light receiving surface of the luminance meter and the longitudinal direction of the core was set to 90 degrees.

The measurement results are shown in FIGS. 2 and 3.

2 shows a change in luminance with respect to distance from a light source, i.e., evaluation of uniformity in the longitudinal direction of the luminance. The optical fibers of Examples 1 and 2 have higher uniformity than the optical fibers of Comparative Example 2. In Comparative Example 2, although the luminance is very high at the position close to the light source, the luminance decreases relatively rapidly as the measurement position moves away from the light source. On the other hand, in the optical fibers of Examples 1 and 2, the degree to which the luminance decreased as the measurement position moved away from the light source was very small.

In Comparative Example 1, the luminance was very low over the entire length direction of the optical fiber compared to the optical fibers of Examples 1 and 2.

As is clear from the above measurement results, the optical fibers of Examples 1 and 2 are more suitable as the optical illuminators for the illumination than the optical fibers of Comparative Examples 1 and 2.

3 shows the luminance change with respect to the measurement angle at a position where the distance from the light source is 2 mm. In Fig. 3, the horizontal axis represents the angle between the normal of the light receiving surface of the luminance meter and the longitudinal direction of the core.

In this case, the direction parallel to the cladding side surface and toward the one end to which the light source was connected was 180 degrees, and the direction parallel to the cladding side and toward the other end was zero degrees, that is, 0 °.

The optical fiber of Example 1 improves the brightness of the light component close to the vertical with respect to the cladding side compared to the optical fiber of Comparative Example 1 having no cladding layer. Therefore, since light having a low angle is diffused by providing a light diffusion layer on the outermost surface, it is possible to effectively increase the luminance of the light component close to the side of the cladding.

(Bending rating)

The optical fiber of the Example was cut to 1 m in length, and the operation of bending the bending fiber at a bending angle of 90 ° at 8 times the radius of curvature (r = about 10 mm) of the core diameter was repeated 10 times. It was then evaluated for the occurrence of layer separation in the cladding. In the optical fibers of Examples 1 and 2, no separation occurred between the first layer and the second layer, and no change in appearance occurred when the light source was connected before and after the flexible test.

The side-emitting optical fiber of the present invention has a uniform side emission luminance over the longitudinal direction even when relatively long. In addition, the optical fiber of the present invention can effectively prevent layer separation between the second layer light diffusing layer and the first transparent layer in contact with the core even when the core diameter is relatively large.

Claims (4)

In a side-emitting optical fiber comprising a core and a cladding disposed around the core, The cladding is composed of a transparent first layer in contact with the core, and a light diffusing second layer formed around the first layer, wherein the two layers are integrally molded. The side-emitting optical fiber of claim 1, wherein the first layer has a thickness of 50 μm to 300 μm. The side-emitting optical fiber of claim 1, wherein the core has a diameter of 5 to 30 mm. The side-emitting optical fiber according to claim 1, wherein the cladding has a two-layer structure formed by coextrusion of two kinds of materials for producing the first layer and the second layer.