Optical waveguides – Optical fiber waveguide with cladding – Utilizing nonsolid core or cladding
Reexamination Certificate
2000-06-15
2003-01-14
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing nonsolid core or cladding
C385S142000, C385S144000
Reexamination Certificate
active
06507688
ABSTRACT:
The invention concerns a liquid light guide as set forth in the classifying portion of claim
1
.
Light guides or optical waveguides with a liquid core are generally known. They generally comprise a flexible sheath tube with an inner coating comprising an amorphous polymer and a light-conducting aqueous solution in the interior of the tube.
German patent application DE-OS No 42 33 087 discloses a liquid light guide which includes a cylindrical tubular sheath comprising a fluorocarbon polymer, and a core surrounded by the sheath and comprising a light-conducting aqueous solution. On its inside the sheath is covered with a thin layer comprising a completely amorphous copolymer which is based on a combination of tetrafluoroethylene and a perfluorinated cyclic ether. The copolymer which constitutes the inner layer can be obtained from DuPont under the trade name Teflon® AF.
Teflon® AF can be dissolved in given perfluorinated liquids only in the range of a few percent, in which respect suitable solvents are the fluorinated liquids FC 72, FC 75 (perfluoro-n-butyl tetrahydrofuran), FC 77 or FC 40 from 3 M. The procedure for applying the AF-layer to the inner surface of a fluorocarbon tube such as for example Teflon® FEP is implemented in a simple manner by once wetting the inside surface of the tube with the Teflon® AF-bearing solution and then evaporating the solvent by means of a flow of air or reduced pressure. The thickness of the layer obtained in that way is only a few &mgr; which in the case of a Teflon® FEP substrate tube or a Hyflon® MFA tube, is sufficient for smoothing tube unevenness and for improving the total reflection of visible and ultraviolet rays as FEP and MFA tubes can be extruded with a very smooth inside surface (degree of roughness: 10
−2
-10
−1
&mgr;). The advantages of the total-reflection Teflon®-AF layer lie in the extremely low refractive index of the material in the range of between 1.29 and 1.32, absolute transparency which is comparable to quartz glass, and chemical inertness. The aqueous salt-bearing solutions such as chlorides or phosphates which are described in DE 24 06 424 C2 and DE-OS No 40 14 363.5 and which have already proved their worth in a market situation for over twenty years are preferred as liquids for light guides, because of their photochemical stability in the ultraviolet spectral range. Those liquids such as for example CaCl
2
in H
2
O, NaH
2
PO
4
in H
2
O should have a refractive index which is higher than that of the total-reflection Teflon® AF layer, in which respect, because of the extremely low refractive index of the Teflon® AF layer, it is already possible to use refractive coefficients as from n=1.36 for the liquid. A value of at least 50° for the optical aperture angle 2&agr; should be achieved, in which respect &agr; can be calculated by means of the simple formula:
sin &agr;={square root over (
n
core
2
−n
sheath
2
)}
Liquid light guides having a core comprising an aqueous phosphate solution such as for example a solution of NaH
2
PO
4
in water, which has a particularly high level of photochemical stability in the short-wave ultraviolet UVB and UVC spectral range (see P 40 14 363.5) can actually only be implemented by using a total-reflection layer with a refractive index of about 1.31 such as for example with Teflon® AF 1600, as solutions of that kind do not permit a substantially higher refractive index than n=1.38 because of salt precipitation in the cold.
The use of Teflon® AF for the inner coating of light guide tubes is however not entirely without its problems.
Layers comprising Teflon® AF only have good adhesion to substrates which like AF also comprise fluorocarbon polymers, in particular after the implementation of a heat-treatment process in which the layer and the substrate tube have to be heated to temperatures to above the glass transition temperature (Tg) of the AF-modification used.
In the heat treatment process which improves adhesion and which has been previously described by DuPont, the layer-substrate system has to be heated to temperatures above 160° C. and, depending on the respective modification of the AF material, even above 240° C., which really is only tolerated by substrate materials comprising fluorocarbon polymers.
In addition, mention is to be made of the low degree of solubility of the Teflon® AF-modifications in the perfluorinated solvents FC75/FC77 (3M), which does not always make it possible, in particular when dealing with substrate tubes of Teflon® PFA, to produce the required minimum layer thickness of up to 5&mgr; by a single wetting procedure for the inside surface of the tube with the Teflon AF-solution, in particular when using the AF-modifications with Tg>160° C.
In comparison with extruded tubes comprising Teflon® FEP, extruded tubes of Teflon® PFA have a greater degree of roughness in respect of the inside surface (>10
−1
&mgr;) and therefore, for optimum optical total reflection require a greater thickness in respect of the inner layer than coated FEP tubes.
A serious disadvantage of Teflon® AF lies in its extremely high cost of US$ 10.00 per gram, which makes a markedly significant difference in terms of manufacture of the liquid light guides.
It would also be desirable also to have available an optical coating material for total reflection, for other substrate materials than Teflon® FEP, in order to be able to manufacture liquid light guides with different mechanical properties such as for example enhanced flexibility. A coating material of that kind should have a substantially increased degree of solubility, in comparison with Teflon AF, in fluorinated liquids, so that by a single wetting process it is possible to produce layer thicknesses of up to 5&mgr;, as are required for example for coating Teflon® PFA or THV (3M) tubes.
That coating material would preferably be a perfluorinated amorphous polymer which has a glass transition temperature markedly below 160° C. so that it is also possible to use substrate materials consisting of THV (3M), polyurethane, polyolefin, polyethylene, silicone and others, which can be thermally loaded to a lesser degree. Such substrate materials require drastically greater layer thicknesses just because of their substantially higher refractive index as, in contrast to perfluorinated substrate tubes such as Teflon® FEP, they do not perform any supporting function in terms of total reflection, in particular when their refractive index is higher than that of the filling liquid.
Furthermore such a perfluorinated coating material which is an alternative to Teflon® AF should be very substantially transparent or amorphous, it should have a refractive index which is as far as possible below that of H
2
O and which like Teflon® AF is also soluble in certain perfluorinated liquids such as FC 75 or FC 77 from 3M, but preferably to an enhanced degree, so that a simple coating process for the inside surface of plastic tubes is possible by once wetting same with the solution of the amorphous fluoropolymer.
Finally it would be desirable if the perfluorinated amorphous copolymer, as an alternative to AF, were simpler to manufacture and could thus be offered on the market at a price markedly below US$ 10.00 per gram.
It will be appreciated that it is also important that the alternative coating material has good adhesion to Teflon® FEP or Hyflon® MFA or THV (3M), the most important tube materials for liquid light guides, or at any event after implementation of a heat treatment process above the glass transition temperature of the coating material.
Ausimont S.p.A. in EP 0 633 257 B1 and EP 0 803 557 A1 describes a perfluorinated copolymer of tetrafluoroethylene (TFE) which, besides TFE also contains a further perfluorinated monomer in the form of a cyclic perfluorinated fluorodioxole involving the following structure:
wherein R
F
can be a perfluoroalkyl having between 1 and 5 C-atoms and X
1
and X
2
, independently of each other, can be —F or —CF
3
.
Besides this novel cyclic perfluorinated fluorodioxole,
Rahll Jerry T
Ullah Akm E.
LandOfFree
Light guide with a liquid core does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light guide with a liquid core, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light guide with a liquid core will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3043126