Fluorinated glasses

Details Fluorinated glasses Fluorinated glasses

1995-04-18

1996-01-02

Bell, Mark L.

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

501 37, C03C 332, C03C 1304

Patent

active

054808456

DESCRIPTION:

BRIEF SUMMARY
This invention concerns fluorinated glasses which can be used in optics, in particular in the infrared band, and which can be used in the manufacture of optical fibers.
Numerous studies have emphasized the interest in glasses made of heavy metal fluorides for optical transmission of up to 7 micrometers and especially the transmission by optical fibers. Further details can be found in the following specialized reference works: "Fluoride Glasses", edited by Alan Comyns, published by John Wiley & Sons in 1989, and "Fluoride Glass Fiber Optics", edited by Ishwar Aggarwal and Grant Lu, published by Academic Press in 1991.
Among the major applications of fluorinated glasses is the transmission by optical fibers in technical fields such as, for example, telecommunications, optical fiber sensors, infrared instruments and medical uses, in particular, laser surgery. In all of these applications, conventional fluorinated glasses which belong to the fluorozirconate family or fluoroaluminate family are restricted to about 4 micrometers in infrared transmission.
For this reason, attempts have been made to produce fluorinated glasses which are transparent in a wider spectral range. Standard compositions, which enable the value of the maximum transmissible wavelength to be increased, are known. Light, small and highly charged cations, for example Li.sup.+, Ti.sup.4+, Zr.sup.4+, Nb.sup.3+, Al.sup.3+ must be excluded. This condition is realized in several families of fluorinated glasses, such as those based on scandium, thorium, gallium and indium fluorides. In particular, Fluoroindate glasses appear promising since they display the least amount of phonon energy. Fluoroindate glasses are mentioned in FR-A-2 478 618 and EP-A-O 036 373. Numerous studies have since been carried out; reference is made, in particular, to the article "Fluoroindate Glasses" by M. Poulain, M. Poulain [sic], Y. Messadeq and A. Soufiane, published in the book "Solid State Optical Materials" in tile series "Ceramic Transactions" of the American Ceramic Society, 1992.
The simplest fluoroindate glasses are binary compositions, such as InF.sub.3 --BaF.sub.2. Since increasing the number of constituents is one of the conventional ways of stabilizing glasses, the compositions used as a base in manufacturing solid samples most often combine InF.sub.3 with various divalent fluorides such as BaF.sub.2, PbF.sub.2, SrF.sub.2, CdF.sub.2, CaF.sub.2, ZnF.sub.2. It was also observed that yttrium fluoride stabilized InF3-BaF.sub.2, that lanthanum fluoride can be incorporated in a limited quantity and that fluorogallate glasses were usually miscible with fluoroindate glasses. Finally, thorium fluoride, whose vitrifying properties are well known, also makes it possible to increase the stability of fluoroindate glasses and decrease the quantity of indium fluoride required to obtain proper vitrification.
Thus, fluoroindate glasses having increased stability are known and their compositions are as follows:


______________________________________ BIZYbT 30 InF.sub.3, 10 ThF.sub.4, 20 ZnF.sub.2, 30 BaF.sub.2, 10 YbF.sub.3 IZBS 40 InF.sub.3, 20 ZnF.sub.2, 20 BaF.sub.2, 20 SrF.sub.2 PZIGL 17 InF.sub.3, 19 ZnF.sub.2, 43 PbF.sub.2, 17 GaF.sub.3, 4 LaF.sub.3 ______________________________________
Adjustments in the composition of the first two glasses, BIZYbT and IZBS, were made, in particular, by replacing InF.sub.3 by GaF.sub.3, YbF.sub.3 by YF.sub.3 or LuF.sub.3, ThF.sub.4 by ZrF.sub.4 or HfF.sub.4, ZnF.sub.2 by MnF.sub.2, BaF.sub.2 by PbF.sub.2, and SrF.sub.2 by CdF.sub.2. These experiments, which have been described in the literature, have enabled one to obtain solid samples which are approximately one centimeter thick. However, satisfactory optical fibers cannot be derived from these samples. Various laboratories have demonstrated the occurrence of superficial devitrification leading to numerous mechanical and optical defects. Moreover, certain compositions deemed to be favourable contain a considerable amount of thorium. As thorium is naturally radioactive, c

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Chem. Abstracts vol. 104 No. 12 Ab. No. 94043g Nishii et al. Aug. 1985.

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