LV11644B - A side-emitting optical fibre - Google Patents

Abstract

The invention relates to optics andtechnology can be used in lighting fixtures, design showcases and interiors; The proposed optical fiber (Fig. 1), which emits light through the side surface, contains a transparent core with refraction index nv light reflective cover with refractive index index n2, with n2 <n1, and a transparent exterior protective coating. Reflective casing material particles are introduced which scatter (reflect, refract) light. The method for obtaining said optical fiber comprises: extraction of a fiber core from a quartz blank, when heated, liquid light-reflecting polymer coating application to a core with subsequent thermal or UV polymerization and coating with a protective material, wherein in a liquid reflecting material housing, for example of silicone before being applied to the quartz core mix light scattering particles, such as metal oxide crystals, with concentrations ranging from 0.1 to 20% by weight of the total composition

Description

LV 11644

SIDE-EMITTING OPTICAL FIBRE

The invention relates to optics and may be used in technology as an illuminating device, e.g. for dressing shop windows, interiors, where elements with light guides are employed.

Optical fibres emitting through the side surface are known where the side emission from a localized area of an optical fibre is achieved by bending the axis of a fibre (WO 90/00699, 25.01.90); by changing the diameter of a core including the use of a core having conical configuration; by introducing a section with increased refraction index n., &gt; n2 into a core, where n., is the refraction index of a core (APPLIED OPTICS, vol.29, No.30, 20 October 1990, p.p.4481); by local deformation of a core or a cladding; by introducing local scattering centres (defects) into a core or on its surface of contact with a reflecting cladding.

Optical fibres emitting through the side surface are also known wherein continuous lateral emission occurs along the entire length of an optical fibre and is achieved by introducing ancillary construction components into a fibre, for instance, a cylindrical cavity filled with gas or containing scattering substance vvithin a core (SU Patent No.1695030A, 1989); forming an air gap betvveen a core and a reflecting cladding (WO 87/07959,17.07.87); an additional scattering layer on the outer surface of a reflecting cladding (Patent application FR 2.609.778 (A^, 16.01.87).

Optical fibres emitting through the side surface are known to have been constructed by employing ancillary components thereof having a sufficiently large outside diameter. Manufacturing of said fibres is connected with the necessity of using a special sophisticated technology of dravving optical fibres which is significantly different from the conventional one, thus leading to prohibitively high production costs of the product.

In accordance with the present invention construction and technology of manufacturing of a side-emitting optical fibre are simplified.

For purposes of this invention conventionally used materiāls are employed in a reflecting cladding, except that scattering (reflecting or refractive) pārticies are introduced at a concentration range from 0.01% to 20% of the total mass without altering geometrical parameters of an optical fibre.

Dravving shovvs a cross-sectional view of an optical fibre. -2-

The side-emitting optical fibre comprises a transparent core 1 with the refractive index of n-ļ and a reflective cladding 2 with the refractive index of n2, where n., is greater than n2, and a transparent external protective layer 3 vvhereof due to the total internai reflection upon the boundary surface of 1-2, the optical fibre ensures transfer of optical emission in the direction of an axis of a fibre. It is known that during the process of emission the wave of emission to some extent penetrates the cladding of material 2. The penetration depth is comparable to the vvavelength of transmitted emission.

Provided fine pārticies either have a reflecting surface with respect to incident emission or the said pārticies are transparent having the refractive index n1 &lt; n2, i.e., causing change in the angle of refraction thereof, core emission in the cladding 2 adjacent to a boundary surface interact with pārticies 4 and may change direction of propagation such that some part of a portion of beams fail to return into a core, instead falling into the cladding 2. Further this portion of emission is scattered diffusively by other pārticies 4 dispersed in the cladding 2 and through the protective layer 3 is emitted in the surrounding space. If the concentration of pārticies 4 in the cladding 2 is sufficiently high, emission through the lateral surface exhibit diffusively uniform spatial distribution. Thus an optical fibre may be used in a novel capacity of a non-conventional cylindrical source of light. A method of forming an optical fibre is as follovvs.

To make a complete use of a quartz preform throughout the process of the fibre dravving, a quartz rod is attached to a preform; after that the preform is subjected to Chemical etching in a 40% solution of hydrofluoric acid for a period not exceeding 60 min at room temperature. Further the quartz preform is treated in an hydrogen-oxygen flame, the duration of treatment depends upon the surface quality of a preform achieved after the etching process is completed.

To achieve a more uniform distribution of the scattered emission, the follovving polymer composition is prepared to be applied to a fibre in order to make a reflecting cladding: a) 100 g of Silicone resin, e.g. 159-305 part A is thoroughly mixed with 1 g of ZnO; b) obtained mixture is filtered; c) 10 g of Silicone resin, e.g. 159-305 part B are added and mixed thoroughly; d) obtained composition is ķept in vacuum. LV 11644 -3- A fibre of the required diameter, for instance 0.4 mm, is dravvn from the preform the free end of which is heated, e.g. in a hydrogen-oxygen flame, using the said equipment; further the fibre passes through a cooler and a spinneret, vvherein the fibre is covered with the said composition for obtaining a scattering layer, further traversing two furnaces used for polymerization at temperatures of 320°C and 300°C, respectively, further a fibre is served into a drawing equipment and reeled up.

Obtained fibre is being dried for 24 hours at a temperature of 40°C.

Technique of extrusion is employed to cover the obtained fibre with a layer of polyamide having the required thickness, to yield, for instance 1 mm outer diameter.

Taking into account the relatively small diameter (ca 1 mm), flexibility and a considerable length (more than 100 m) of an optical fibre, the aforementioned technique potentiates significant advantages in comparison with conventional cylindrical light sources - daylight valves, neon tubes etc. LV 11644

CLAIMS 1. A side-emitting optical fibre comprising a transparent core, reflecting cladding and outer protective layer, provided n., is greaterthan n2, where n, and n2 are refraction indexes of a core and a reflecting cladding, respectively, vvherein light scattering pārticies are additionally introduced into the material of a light reflecting cladding. 2. Optical fibre as claimed in claim 1 vvherein material refraction index n2 with additionally dispersed light scattering pārticies forms a light reflecting cladding. 3. Optical fibre as claimed in claim 2 vvherein a core is formed of quartz and a reflecting cladding of polymer, for instance, polyamide. 4. Optical fibre as claimed in claims 2 or 3 vvherein one or several axial sections of a reflecting cladding are formed of material having the refraction index of n2 vvithout adding light scattering pārticies. 5. Optical fibre as claimed in any previous claim vvherein one or several its axial sections are formed by adding light scattering pārticies at various concentrations. 6. Optical fibre as claimed in any claim 2, 3, 4 or 5 vvherein apart from light scattering pārticies or instead of these, luminescent materiāls are introduced into a light scattering cladding. 7. A method of forming a side-emitting optical fibre in accordance to any previous claim, comprising the steps of dravving the core of a fibre from a quartz preform by heat treatment, applying a liquid reflecting polymer layer to a core follovved by a subsequent thermo- or UV-polymerization and covering it with a protective layer vvherein prior to applying liquid material of a reflecting cladding, silicone resin, for instance, to a quartz core, light scattering (reflecting, refracting) pārticies are mixed in, for instance, crystals of mētai oxide at concentration values ranging from 0.01% to 20% of the total mass of a composition. LV 11644

ABSTRACT

The invention relates to optics and may be used in technology as an iliuminating device, e.g. for dressing shop windows, interiors, where elements with light guides are employed.

The side-emitting optical fibre comprises a transparent core with the refractive index of nA and a reflective cladding with the refractive index of n2, where n., is greater than n2l and a transparent external protective layer. Light scattering (reflecting, refracting) pārticies are introduced into the material of a light reflecting cladding. A method of forming an optical fibre emitting through the lateral surface comprising the steps of dravving the core of a fibre from a quartz preform by heat treatment, applying a liquid reflecting polymer layer to a core follovved by a subsequent thermo- or UV-polymerization and covering it with a protective layer vvherein prior to applying liquid material of a reflecting cladding, silicone resin, for instance, to a quartz core, light scattering (reflecting, refracting) pārticies are mixed in, for instance, crystals of mētai oxide at concentration values ranging from 0.01% to 20% of the total mass of a composition.

Claims (7)

EN 11644 DESCRIPTION OF THE INVENTION 1. A laterally radiating optical fiber comprising a transparent core, a light-reflecting casing and an outer protective coating having the condition n., &Gt; n2, where n, and n2 are the refractive indices of the cores and the light reflecting material respectively, in that the light-reflecting casing material further comprises light-scattering particles. Optical fiber according to claim 1, characterized in that the light-reflecting casing is formed of a material with refractive index n2, in which additional light-scattering particles are dispersed. 3. Optical fiber according to claim 2, characterized in that the core is made of quartz and a reflective coating of polymer material, such as polyamide. Optical fiber according to claim 2 or 3, characterized in that one or more axial sections of its reflective casing are made of a material of refractive index n2 without the addition of light scattering particles. 5. Optical fiber according to any one of the preceding claims, characterized in that one or more axial stages thereof are formed by the addition of different concentrations of light scattering particles. The optical fiber according to any one of claims 2 to 5, characterized in that luminescent substances are added separately to the light scattering particles or instead of the light scattering particles. A method of producing a laterally radiating optical fiber according to any preceding claim, comprising stretching the core of the fiber from the quartz sheet by heating it, applying a liquid-reflective polymer casing to the core with subsequent polymerization by thermal or ultraviolet radiation and coating with a protective material; characterized in that prior to application to the quartz core light reflecting casing in a liquid material such as silicone, disperse light-scattering particles such as metal oxide crystals at a concentration of 0.01% to 20% of the total weight of the composition.