WO1993009451A1

WO1993009451A1 - Plastic optical waveguide

Info

Publication number: WO1993009451A1
Application number: PCT/DE1992/000890
Authority: WO
Inventors: Nikolaos Douklias; Wolfgang Rogler
Original assignee: Siemens Aktiengesellschaft; Microquartz Gesellschaft Für Quarzglaskomponenten Mbh
Priority date: 1991-10-28
Filing date: 1992-10-23
Publication date: 1993-05-13
Also published as: DE4135523A1

Abstract

In order to produce plastic optical waveguides having a high thermal resistance, a first coating of a reaction resin which is photoconductive in its cured state and which has the required mechanical properties is applied on a substrate material shaped as a glass or plastic fibre or as a bunble of such fibres. This reaction resin is cured to form a core of duroplastic material, a second coating made of a reaction resin which adheres well to the core material in its cured state and which has a refractive index at least 1 % lower than that of the core material is applied onto the first cured reaction resin, and the second reaction resin is cured to form a cladding made of duroplastic material.

Description

Plastic optical fiber

The invention relates to a method for producing plastic optical waveguides.

While optical waveguides, i.e. Optical fibers, made of quartz glass, are used for short-range optical fibers made of plastics, i.e. Polymer optical fibers (POF) represent a cost-effective alternative. Plastic optical fibers have a core / cladding structure, the core being made of the best possible light-conducting, i.e. polymer material which dampens as little as possible and the jacket consists of a polymer material which adheres well to the core and has a refractive index which is smaller than that of the core material.

The manufacture of plastic optical waveguides is based on thermoplastic polymers which are produced in a complex polymerization process which leads to a material which is as homogeneous as possible. These thermoplastic polymers are processed - under high purity conditions - in an extrusion or melt spinning process into thin threads which form the core (see: "Chemtronics", Vol. 1 (1986), pages 98 to 106) ). The jacket is also made of thermoplastic material; it is usually applied to the core in a coextrusion process. However, application from a solution is also described (DE-OS 36 07 301).

The core material used in plastic optical waveguides is predominantly thermoplastic (meth) acrylic ester polymers or copolymers; it is also the use ^'of DEU- terated and fluorinated (meth) acrylates described (DE-OS 28 44 754). Furthermore, polystyrene, styrene copolymers and polycarbonate are used as the core material (see: "Kunststoffe", Vol. 79 (1989), pages 1040 to 1044). Partly fluorinated acrylate or methacrylate polymers or fluorinated polyolefins are usually used as the covering materials (DE-OS 36 07 301). In addition, plastic optical waveguides with a silicone sheath material are also known (DE-OS 38 14 298).

In addition to the cost-effective production, the advantages of plastic optical waveguides - compared to optical waveguides in the form of optical glass fibers - lie above all in the easier handling, and in fact due to the greater flexibility, even with larger fiber diameters. A serious disadvantage is the limited thermal stability. Due to the thermoplastic character, plastic optical fibers can only be used below the glass transition temperature of the core materials. In the coming for this purpose in question polymers but this means an upper temperature limit of about 120 ^β C. As the demands on the Temperatur¬ resistance of plastic optical fibers, however zu¬ taking are higher, for example when used in the automotive sector, is the provision of higher temperature-resistant plastic optical fibers is urgently required.

To increase the temperature resistance, attempts have already been made to produce plastic optical waveguides from thermosetting resin compositions (EP-OS 0 246 613). These resin compositions, which are used to manufacture the core, contain a (meth) acrylic acid esters with a tricyclodecanyl group, a (meth) acrylic acid ester with an alkyl, cycloalkyl or aryl group and a multifunctional monomer which is used for crosslinking. The mixture of these three components is pressed through a heated tube, where it is poly erized and a fiber is formed. The fiber product is then hardened, and a coating is then applied to the resulting core. However, for procedural reasons, such a procedure is not very suitable for practical use, particularly in economic terms.

The object of the invention is to provide a method which makes it possible to use plastic optical waveguides with high temperature resistance in an economical, i.e. procedurally simple to produce.

This is achieved according to the invention in that a first coating of a reaction resin is applied to a carrier material in the form of a glass or plastic fiber or a bundle of such fibers, which in the hardened state is light-conducting and has the required strength properties, that this reaction resin is hardened to a core of thermosetting material, that a second coating of a reaction resin is applied to the hardened reaction resin, which adheres well to the core material in the hardened state and has a refractive index that is at least 1% smaller than that of the core material, and that this reaction resin is hardened into a jacket made of thermosetting material.

In the method according to the invention, the fibers are made of glass or plastic essentially a carrier function, ie they are a processing aid for the applied reactive resins. However, these fibers can also contribute to the light conduction. The glass fibers preferably consist of quartz, the plastic fibers preferably of polyester or of ara id, ie special polyamide. In the method according to the invention, a single fiber can serve as the carrier, but a fiber bundle can also be used which consists of two or more thin fibers. For this purpose, for example, several glass fibers are drawn in a double crucible process and these are then subjected to a coating process together.

In general, the process according to the invention is carried out in such a way that a thin glass or quartz fiber is drawn in a fiber drawing system, which is then coated with one of the core or cladding materials listed below. Thicker core or sheath dimensions can be achieved by multiple coating. Depending on the type of plastic, electric furnaces or UV light sources can be used for curing the plastics.

So-called reaction resins are used in the process according to the invention, i.e. curable or cross-linkable

Resins. Hardening these resins creates plastics that are referred to as thermosets.

For the first coating process, i.e. for the production of the light-guiding core are in the invention

In principle, the process is suitable for all reactive resins which are sufficiently transparent on the one hand and those which are suitable for such a coating process on the other hand Viscosity, adhesion and hardening characteristics and - in the hardened state - have the necessary strength properties. In principle, many of the materials that are used for coating glass fibers with a step or gradient index profile are therefore suitable for this purpose.

Acrylate and methacrylate resins have proven to be particularly suitable for the process according to the invention; Such resins usually represent mixtures of mono- and di- or polyfunctional components. (Meth) acrylate resins are esters of (meth) acrylic acid with mono- and di- or polyfunctional alcohols. Aliphatic and cycloaliphatic as well as aromatic alcohols are possible. Fluorinated and deuterated (meth) acrylate resins are also suitable for the production of core materials. Silicoπ- (meth) acrylates can also advantageously be used, in particular dimethylpolysiloxane (meth) acrylates. To produce the core materials, the resins can be cured thermally, both with and without the addition of suitable peroxides, or — with the addition of suitable photosensitizers — by UV radiation. Thermal addition-crosslinking silicones are also suitable for the production of the core materials.

After curing, the reaction resins used in the second coating process must first of all lead to a cladding material with a refractive index that is at least 1% smaller than the underlying core material. In principle, all thermally or

UV-curable reactive resins that meet this requirement. Suitable starting materials are in particular (meth) acrylate resins, which can be fluorinated in whole or in part. NEN, as well as silicone (meth) acrylates. These resins can be curable both thermally and by UV radiation. Addition-crosslinking silicones can also be used. In individual cases, the reaction resin used for the cladding material must be matched to the underlying core material with respect to the refractive index.

The operating temperature of the plastic optical waveguide according to the invention is -40 to 150 ^β C or above. To protect the plastic optical waveguide, it can be expedient to apply a further coating to the jacket. For this purpose, either - by means of a further coating process - a suitable reaction resin can be applied, which is subsequently cured, or - by means of an extrusion process - a thermoplastic polymer .

The invention will be explained in more detail using exemplary embodiments.

A fiber drawing system is used to produce a plastic optical waveguide according to the invention. In this drawing system, a rod made of glass or quartz is continuously lowered into an HF or electric furnace (made of graphite) with the aid of a motor. A thin glass fiber is drawn from the rod end in the heating zone, which serves as a carrier material. This glass fiber is then passed through a coating device for the core material and a first electric furnace or a first UV source and subsequently through a coating device for the cladding material and a second electric oven or a second UV source. The coated glass fiber is then wound onto a drawing drum. Before the coating device for the core material and after the second electric furnace or the second UV source, the thickness of the glass fiber or the plastic optical waveguide is expediently checked with a fiber strength measuring device.

Examples 1 to 5

A 90 μm thick fiber is drawn from a quartz rod. This fiber is coated in a first coating device with a reaction resin for the core material. After curing, which takes place thermally in an electric furnace (500 W) or by UV radiation using a mercury vapor lamp (80 W / cm), a POF core with a diameter of 160 μm is obtained. This core is then immediately coated in a second coating device with a reaction resin for the cladding material, and curing is subsequently carried out. The respective cladding material is applied with a thickness such that a plastic optical waveguide with an outer diameter of approximately 225 μm is present after hardening. The drawing speed is approx. 0.2 m / s.

The attenuation behavior at room temperature was tested at 835 n in the case of the plastic optical waveguides produced in the manner described. The results obtained and the core and shell materials used are summarized in Table 1.

The values given in Table 1 show that the method according to the invention can be used to produce plastic optical waveguides with technically useful attenuation in a rational manner. Table 1

example

Core material; Fluoro-fluoro-acrylate silicone acrylate acrylate acrylate

Viscosity at 25 ^β C (in mPa.s): 2000 2000 8000 4000 8000

Refractive index: 1.416 1.416 1.518 1.41 1.518

Hardening: UV UV UV therm. UV

Shore or Vickers hardness: D70 D70 11 A40 11

Sheath material: fluorine-fluorine-fluorine-fluorine-silicone acrylate acrylate acrylate

Viscosity at 25 "C (in mPa.s): 2000 2000 2000 2000 4000

Refractive index: 1.38 1.35 1.38 1.38 1.41

Hardening: UV UV UV UV therm.

Shore hardness: A82 D43 A82 A82 A40

POF attenuation at 835 nm (in dB / km): 3300 2900 3000

Claims

1. A process for the production of plastic light waveguides, characterized in that a first coating of a reactive resin is applied to a carrier material in the form of a glass or plastic fiber or a bundle of such fibers, which is light-conducting in the hardened state and the required strength properties has that this reaction resin is hardened into a core made of thermoset material, that a second coating of a reaction resin is applied to the hardened reaction resin, which adheres well to the core material in the hardened state and has a refraction that is at least 1% smaller - index than the core material, and that this reac tion ge _¬ is hardened resin to a casing made of duroplastic material.

2. The method of claim 1, d a d u r c h g e - k e n n z e i c h n e t that an acrylate or methacrylate resin or a silicone (meth) acrylate is used as the reaction resin for the core material.

3. The method according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that an acrylate or methacrylate resin or a silicone (meth) acrylate is used as the reaction resin for the jacket material.

4. The method according to any one of claims 1 to 3, d a - d u r c h g e k e n n z e i c h n e t that on the

Coat made of thermosetting material, a coating of a reaction resin is applied and the reaction resin is cured.

5. The method according to any one of claims 1 to 3, that a thermic polymer is applied to the jacket made of thermosetting material.