Patent Application
20090257721
The disclosure relates to an optical transmission element having high temperature stability, in which at least one optical waveguide is arranged in a buffer tube. The disclosure also relates to an optical cable with an optical transmission element in which at least one optical waveguide is arranged in a buffer tube. The disclosure also relates to a method for producing such an optical transmission element and to a method for producing such an optical cable.
In the case of an embodiment of an optical cable, so-called micromodules as optical transmission elements are surrounded by a cable jacket. A micromodule contains a number of optical waveguides which are surrounded by a thin buffer tube. The purpose of the micromodules is the bundling of a number of optical waveguides and their identification by color. At present, the buffer tube of a micromodule consists of polymer blends that are extruded as a thin buffering layer around the optical waveguides in extrusion installations for thin-layer extrusion.
In the extrusion installations, the polymer blends are melted. In the extrusion operation, the molten polymer blend is forced through dies and extruded as a buffer tube around the optical waveguides and the filling composition. Polymers are long-chain molecules, which are particularly difficult to process when thin layers, for example buffer tubes, are being produced. The thin-layer extrusion of polymer materials at high speeds is technically challenging in particular. At present, increasing the processing speed of the molten polymer during the extrusion operation and reducing the layer thicknesses of the tube of a micromodule presents a technical problem. Further difficulties arise from the fact that polymer materials can only be used in low temperature ranges. The low-melting polymer materials that are currently used have a melting temperature of between 70° C. and 80° C.
An optical transmission element which is produced using materials that can be easily processed and allow a wide range of applications is to be specified hereinafter. It is also desirable to specify an optical cable which contains optical transmission elements that can be easily processed and can be used in a broad range of applications. There is also a need to specify a method for producing an optical transmission element in which materials that can be easily processed and make a wide range of applications of the optical transmission element possible are used. A method for producing an optical cable using optical transmission elements which contain materials that can be easily processed and allow the optical cable to be used in a wide range of applications is also to be specified.
According to a possible embodiment of the optical transmission element, the optical transmission element comprises at least one optical waveguide which contains a glass fiber. Furthermore, the optical transmission element comprises a tube, which surrounds a space in which the at least one optical waveguide is contained. The tube is formed from a material which comprises a resin.
Previously, polymer blends have been used for producing such tubes, for example buffer tubes, of optical transmission elements. The enclosing of the individual optical waveguides took place on extrusion installations for thin-layer extrusion. The thin-layer extrusion of polymers at high speeds presents a technical problem in particular. Furthermore, for an optical transmission element, the buffer tube should be easily removed. For this purpose it is necessary, for example, for the layer thickness of the buffer tube to be reduced. With the use of polymer blends as the material for the buffer tubes, at present it appears to be no longer possible to the greatest extent to obtain both further increases in speed and a reduction in the layer thicknesses for technical reasons. Furthermore, the polymer systems that are currently used only allow restricted temperature ranges. For instance, in the case of an optical transmission element in which a polymer blend is used as the material for its buffer tube, an operating temperature of 70° C. to 80° C. should not be exceeded.
Several advantages are achieved by the use of resin systems instead of thermoplastic polymers. For example, higher processing speeds can be achieved. Furthermore, optical transmission elements having buffer tubes formed from a resin material have a higher temperature stability. The resin system is chemically devised in such a way that easy removal of the tube is possible by adjusting the oligomers and/or fillers of the resin, for example of an acrylic resin.
The material comprising the resin of the tube may contain an acrylate. A filler may also be mixed into the material comprising the resin of the tube. For example, inorganic materials may be mixed as fillers into the resin. Furthermore, glass fiber offcuts, chalk or magnesium hydroxide may be mixed as a filler into the material comprising the resin of the tube.
When the material is irradiated with light, a network structure may form in the material comprising the resin of the tube. The material comprising the resin of the tube may, for example, contain photoinitiators, a network structure forming in the material comprising the resin of the tube when the photoinitiators are irradiated with ultraviolet light.
The material comprising the resin of the tube may, for example, comprise molecules of methacrylic acid.
The at least one optical waveguide is, for example, movably arranged in the space surrounded by the tube. The space surrounded by the tube may also contain a filling composition. The filling composition may, for example, contain mineral or paraffin oils. It may also contain a material comprising rubber or aerosil.
The at least one optical waveguide may comprise a cladding which compactly surrounds at least one glass fiber. For example, the cladding which surrounds the at least one glass fiber may likewise be formed from the material comprising the resin.
An optical cable comprises at least one optical transmission element according to one of the aforementioned embodiments. Furthermore, the optical cable has a cable jacket which surrounds a space in which the at least one optical transmission element is contained.
The at least one optical transmission element is movably arranged in the space surrounded by the cable jacket. Furthermore, it may be provided that the space surrounded by the cable jacket contains a filling composition.
A method for producing an optical transmission element is specified hereinafter.
According to the method, it is provided that at least one optical waveguide which contains a glass fiber is provided. A space in which the at least one optical waveguide is contained is surrounded with a tube, the tube being formed from a material which comprises a resin.
A material which contains an acrylate may be used as the material comprising the resin. A material which contains molecules of methacrylic acid may be used as the acrylate. A material which contains inorganic fillers may also be used as the material comprising the resin. Glass fiber offcuts, chalk and/or magnesium hydroxide may be used, for example, as inorganic fillers.
Before the step of surrounding the at least one optical waveguide with the tube, the at least one optical waveguide is surrounded with a filling composition. The step of surrounding the at least one optical waveguide with the filling composition and the step of surrounding the filling composition with the tube may, for example, take place at the same time. The step of surrounding the at least one optical waveguide with the filling composition and the step of surrounding the filling composition with the tube may, for example, take place by the at least one optical waveguide being wetted with the filling composition and at the same time the filling composition being wetted with the material comprising the resin. For example, the filling composition and the resin system may be applied in one operation by means of double-layer wetting. The optical waveguides to be coated may in this case run through a single tooling system. Since only one tooling system is used, it is made easier for a machine plant to be started up and operated. The double-layer wetting also allows higher production speeds to be achieved and thinner buffering layers to be formed than is possible when the tube is produced with a heated polymer blend. For example, production speeds of between 500 and 700 m/min can be achieved and a thin buffering layer of between 0.05 mm and 0.5 mm can be produced by the use of resin systems.
According to the method, the material comprising the resin can be cured by irradiating with light after the step of wetting the at least one optical waveguide with the filling composition and the material comprising the resin.
According to a method for producing an optical cable, at least one optical transmission element is produced in accordance with one of the aforementioned embodiments. The at least one optical transmission element is surrounded with a cable jacket.
It is to be understood that both the foregoing general description and the following detailed description present exemplary embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the detailed description, serve to explain the principles and operations thereof
Instead of the previously customary polymer blends, the tube 30 of the optical transmission element contains a material comprising a resin. The tube 30 may, for example, contain acrylates. The acrylates used are preferably molecules of methacrylic acid. They contain monomers with a short chain length and oligomers with a longer chain length. The mechanical properties of the acrylic resin, such as for example hardness, elongation at break and deformability, can be adjusted by means of the proportion of oligomers in the acrylates. The higher the proportion of oligomers, the harder the resin, and consequently the harder the tube 30 of the optical transmission element.
Furthermore, fillers may be mixed into the material comprising the acrylates of the tube 30. Inorganic materials are substantially used. For example, chalk or magnesium hydroxides are used. Furthermore, it is possible additionally to embed glass fiber offcuts 31 in the acrylates. The resin system of the tube 30 is preferably formed as an acrylate system, which when irradiated with light, for example with ultraviolet light, forms a network-like structure and thereby cures. The same materials that are used for the tube 30 of the optical transmission element may also be used for the cladding 2, which compactly surrounds the glass fiber 1.
Furthermore, in the processing unit V1, the tube 30 is extruded around the filling composition 21 from a material comprising a resin. For this purpose, the processing unit V1 is connected to a container B2, which contains the material comprising the resin (resin system). The resin system substantially comprises an acrylate, which may be mixed with a filler. Inorganic materials are added to the acrylate, for example, as the filler. Fillers of chalk or magnesium hydroxide are used here, for example. Furthermore, glass fibers may also be admixed with the resin system in the processing unit V1. The acrylic resins applied as the tube in the processing unit V1 contain, for example, molecules of methacrylic acid. These comprise monomers and oligomers. The mechanical properties of the acrylic resin, in particular the hardness, elongation at break and deformability, of the tube 30 can be adjusted in the processing unit V1 by means of the proportion of oligomers used. The more oligomers are contained in the acrylic resin, the harder the tube 30.
The tube 30 and the filling composition 21 are applied, for example, in one operation. The application of the filling composition 21 to the optical waveguides 10 and the surrounding of the filling composition 21 with the micromodule tube 30 takes place, for example, by double-layer wetting. The filling composition 21 and the resin systems of the micromodule tube 30 are applied here, for example, through an annular die D. In the processing in the processing unit V1, the material comprising the resin of container B2 is an aqueous solution, which is applied by jetting processes at room temperature.
The use of resin systems that are applied as an aqueous solution allows very high processing speeds to be achieved. The processing speeds in this case lie the range between 500 and 700 m/min. This corresponds to 3 to 4 times the speeds that were possible in the extrusion of polymer materials previously used as the micromodule tube. Furthermore, the buffering layer 30, which is applied as an aqueous solution by a wetting operation, can be of a particularly thin form. With the use of the acrylic resin systems as materials for the buffering layer 30, a layer thickness of the buffering layer in the range from 0.05 to 0.5 mm can be achieved as a result.
After the wetting of the optical waveguides with the filling composition 21 and the resin systems of the tube 30, the aqueous layer of the tube 30 is irradiated with light, for example ultraviolet light. Preferably contained in the material comprising the resin are photoinitiators, which form a network structure when they are irradiated with ultraviolet light within the resin material. When these UV resin systems are completely crosslinked, a thermoset or elastomeric state which cannot be broken down even under great heat exposure is produced. This makes it possible to use the optical transmission elements even in high-temperature environments. The previously used polymer materials, which were generally formed as low-melting thermoplastics, are already molten at 70° C. to 80° C. By contrast, the UV-crosslinkable resin systems used for the tube 30 have a higher thermal stability. The viscosities of the filling material 21 and of the acrylic resins preferably lie between 4000 and 8000 MPas. The use of resin systems for the tube 30 also has the advantage that the material can be pulled or peeled off without any great force being exerted. As a result, easy accessibility to the optical waveguides is made possible.
The micromodules 100 that leave the processing unit V1 are wound up onto a drum after irradiation with UV light and the curing process. To produce a cable 1000 as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006060431.8 | Dec 2006 | DE | national |
This application is a continuation of International Application No. PCT/EP07/063730, filed Dec. 11, 2007, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP07/63730 | Dec 2007 | US |
| Child | 12485273 | US |
