Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Reexamination Certificate
1999-12-01
2002-02-26
Hoffmann, John (Department: 2874)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
C065S409000, C023S30200R
Reexamination Certificate
active
06349572
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of making an optical fiber bundle, comprising individual optical fibers, which are compressed with each other at a common end in a common metallic sleeve, and shaped or formed by application of temperature and pressure. The invention also relates to an apparatus for performing this method. The invention further relates to an optical fiber bundle, which comprises a plurality of individual optical fibers, which are compressed and melted together at a common end in a hexagonal packing.
2. Prior Art
Frequently a flexible fiber optic light guide, comprising a plurality of individual optical fibers, a so-called optical fiber bundle, are used for light transmission. The individual fibers are usually combined at a common end in a sleeve, which, for example, is attached in a lighting apparatus for illumination.
The combination of the individual fibers at a common end to form a bundle requires special design engineering attention.
It is known in the prior art to make an optical fiber bundle by gluing the individual fibers together and bonding them in a sleeve that is pushed onto them. This widely used method has the disadvantage that the adhesive that is used limits the temperature resistance, the packing density and thus the optical transmission which is possible through the optical fiber bundle, because the individual optical fibers retain their circular cross-sectional shape and rest against each other only point-wise with free space. Also the chemical stability is limited which similarly reduces the range of applications in which this type of optical fiber bundle can be used.
Methods are known in which the individual fibers are melted with the sleeve and each other in a common sleeve.
The advantages of this sort of optical fiber bundle include above-all its higher temperature resistance (adhesive-free), higher light transmission, because more individual fibers are present in a cross-section by which hexagonal packing arises when the fibers are melted and compressed, and improved resistance to chemical attack, which is especially noteworthy for thermal disinfection applications and generally for sterilization in medical applications.
Processes are described in DE 26 30 730, in which a heat-softening sleeve is pressed on the optical fiber bundle. The individual fibers are then shaped hexagonally and there are no intervening free spaces between them. However in this prior art process melting between the individual optical fibers does not occur.
Glass sleeves would be advantageous to use because of their lower viscosity properties, but especially have the following disadvantages:
shaping tools cause imperfections and defects during sealing when used in glass sleeves;
the optical fibers are extremely impact- and shock-sensitive when used in glass sleeves (danger of chipping).
In the known method in principle metal sleeves with glass-like thermal and viscosity properties, i.e. the so-called heat-softening metals, could be used.
However these heat-softening metals have disadvantageous thermal and mechanical loads and are not usable in practice.
For protection of the glass sleeve the known method provides an outer metal sleeve surrounding the glass sleeve. The glass sleeve is pushed into a shaping or forming conical end of the outer metal sleeve and is compressed there by means of a slidable press-metal sleeve pushed on the fiber bundle. Then glass sleeve (and the press-metal sleeve) is connected with the outer metal sleeve by gluing or softened glass.
A formation of the end of the optical fiber bundle in this manner however has the following serious disadvantages:
The outer metal sleeve must be sufficiently thick-walled in order to compensate for thermal stresses (compression glass melt). This has the disadvantage that the usable optical surface area is small, in relation to the outer diameter of the metal sleeve.
An additional pressing tool that remains in the light guide ends is required to bring the inner glass sleeve into the outer metal sleeve. Problems result during centering of the optical fiber bundle in the softening glass sleeve, which act disadvantageously on the optical axis.
On inserting the inner glass sleeve into the outer metal sleeve furthermore no melting zone is formed, in which the individual fibers are parallel to each other. The conical convergence of the optical fiber bundle at their ends acts disadvantageously on the reflection properties of the optical fiber bundle.
only bundle diameters up to 10 mm can be made by this technique.
The provision of the outer metallic sleeve finally leads to an end portion of the optical fiber bundle that has three sleeves, namely
the glass sleeve (or alternatively a metallic sleeve made of a heat softening material),
a Press-sleeve,
the outer metallic sleeve, i.e. to a complex expensive termination of the optical fiber bundle as well is as the above-mentioned disadvantages.
There are additional disadvantages. In the known case a forming step, namely the compressing and tapering of the optical fiber bundle with heat and pressure, must be performed before putting on the glass sleeve (or alternatively the heat-softening metal sleeve).
DE 196 04 678 A1 describes a process in which the individual optical fibers are melted together at the end of the optical fiber bundle. Furthermore the entire optical fiber bundle (up to 30 m long) must be rotated to melt the common end, which leads to great manipulation difficulties and to limitations for more complex or larger components. In the known method the individual optical fibers and tools are placed in an electrically heated oven at the softening temperature. The melting process or softening process requires several hours for the case of large diameter components. A definite temperature adjustment of the temperature of the individual optical fibers to be melted is not possible because of the oven structure. Also only easily shaped materials (brass, nickel silver) with a very thin sleeve wall thickness can be used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method for making an optical fiber bundle based on the method according to German Patent Document DE 26 30 730 A1, so that an optical fiber bundle with improved optical properties and a wider range of possible applications results in a simple manner with simple means.
It is another object of the present invention to provide an improved optical fiber bundle having improved optical properties and a wider range of possible applications than the optical fiber bundles currently available in the art.
It is a further object of the present invention to provide an apparatus for making the optical fiber bundle according to the improved method for making it.
According to the invention the method of making an optical fiber bundle from a plurality of individual optical fibers that attains the above objects includes:
temporarily mechanically holding individual optical fibers together in a round and densely packed fiber bundle and pushing it in a snug fit in a single metallic sleeve made from a metallic material that has a sufficient high temperature strength at a forming temperature of the glass in the optical fibers;
installing the optical fiber bundle in a clamping device with the clamping device arranged in the vicinity of the single metallic sleeve in order to hold the optical fiber bundle fixed in an axial and radial direction;
heating the clamped end of the optical fiber bundle pushed in the single metallic sleeve to the forming temperature;
compressing the heated end of the optical fiber bundle in the single metallic sleeve to shape or form the individual optical fibers in a hexagonal packing and pressing in the metallic sleeve on this hexagonal packing, without sealing the single metallic sleeve to the optical fiber bundle;
cooling the shaped end of the optical fiber bundle with the individual optical fibers in the hexagonal packing; and
removing the optical fiber bundle from the clamping device.
The apparatu
Henrich Thomas
Meinl Juergen
Hoffmann John
Schott Glas
Striker Michael J.
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