FR2481262A1 - GLASSES OF FLUORIDES AND OPTICAL FIBERS CONSISTING OF THESE GLASSES FOR TRANSMISSION IN THE INFRARED BAND - Google Patents

Abstract

GLASSES OF FLUORIDES WITH HIGH TRANSMISSIVITY IN THE INFRARED FOR THE PRODUCTION OF OPTICAL FIBERS USEABLE AT WAVELENGTHS NEAR 4MM. THESE GLASSES CONTAIN HAFNIUM FLUORIDE AS THE MAIN NETWORK FORMER, THE FLUORIDE OF A VARIABLE COORDINATION ELEMENT SUCH AS THORIUM, AS A STABILIZER, AND THE FLUORIDE OF ONE OR MORE LARGE ION RADIUS CATIONS SUCH AS THOSE OF BARIUM OR LEAD AS A NETWORK MODIFIER. AN EQUAL MOLAR PERCENTAGE OF BAF AND PBF MAY BE USED, FOR EXAMPLE 16.87 WITH 8.75 THF AND 57.5 HFF.

Description

The present invention relates to fluoride glasses for

  transmission of infrared radiation, more particularly glasses based on hafnium fluoride, and finds special but not necessarily exclusive applications in the manufacture of optical fibers for transmitting infrared radiation. The potential benefit of commissioning fiber optic systems at wavelengths greater than those commonly used - that is, from 0.85 to 1 pm - is that intrinsic losses can in principle be significantly reduced with a weaker Rayleigh scattering component. Conventional silica-based glasses are unsuitable in this case because the absorption of photons produces a rapid increase in attenuation at lengths.

of waves less than 1.8 μm.

  A family of zirconium tetrafluoride glasses has been examined and a first account of this research has been made in the journal Material Research Bulletin 10, 243 (1975). These glasses have a future as an inert material in the chemical and nuclear industries. They also have a certain future in the transmission of infrared radiation because they include species with high atomic weight which are interconnected by relatively long bonds. Experience has shown that zirconium tetrafluoride glasses become opaque to infrared radiation at around 3 μm. However, this is not advanced enough in the infrared to produce a very low attenuation in the region close to the middle of the infrared band, and particularly in a region of special interest around 4 μm. The glasses

  mentioned zirconium tetrafluoride have another disadvantage.

  If they are heated above their transition temperature, they tend to become thermally unstable. Such instability would present very serious problems when stretching a fiber

optical with a glass of this kind.

  According to the present invention, there is provided a fluoride-based glass for transmitting infrared radiation, comprising hafnium fluoride as the main network former and, in molar percentage, at least 40% in network stabilizer aggregate and network modifier; glass in which the network stabilizer is present, in molar percentage, at least 5% and consists of fluoride of a raw several variable coordination elements other than hafnium, the network modifier consisting, him, 4LJ of fluoride of one or more elements whose cations have a

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  valence equal to one or two and an ionic radius at least equal to that of Sr 2 or Pb, in which there is, in molar percentage, up to 15% D in aggregates of other compatible components, and finally in which may optionally replace part of the fluoride content by an equivalent molar percentage in aggregate of other halides. Considering a range of examples, it has been recognized that if a particular composition based on zirconium fluoride forms a glass, an equivalent composition where zirconium fluoride is replaced by an equivalent molar fraction of hafnium fluoride also forms a glass. Comparative measurements made on these two glasses have shown that in each case the transmission of glass to hafnium extends further in the infrared than its zirconium counterpart. This fact has been attributed to the higher atomic weight of hafnium. Emerging issues of thermal instability have been addressed through the appropriate choice of stabilizers and network modifiers. The most commonly encountered glasses consist of a three-dimensional framework of tetrahedral units connected to each other by their vertices. The vertex links have a range of angular freedom that ensures that there is no long-range order in the structure. Examples of glasses of this type

  are given by glasses based on SiO2, GeO2, BeF2 and ZnCl2.

  The use of stabilizers and network modifiers in such glasses is known. Glasses based on hafnium fluoride are supposed to

  be able to form glasses using different mechanisms.

  Hf 4 as Zr 4 is capable of forming 6- or 8-fold coordination polyhedra with differences in both bond lengths and bond angles. A random network of these polyhedra would have no order at a great distance. However, in practice it has been found necessary to add a second component which also has variable coordination properties. This may be, for example, zirconium fluoride, or a fluoride of one of the rare earths such as lanthanum, cerium, praseodynium, neodynium, samarium, europium, gadolinium, terbium, and the like. hafmium or thorium.These fluorides can be used in combination. Stability can also be promoted by the inclusion of network modifiers with many low valence cations such as

+1 +1 +2 +2

  Cs', he, Sr, and Pb. To these we can add a small amount

+1 +2 +2 +1

  smaller ions such as AI, Na, Ca, Mg and Li The extent of infrared transmission depends on

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  the use of heavy elements weakly related to each other. Weak links tend to be associated with properties

  mediocre mechanics, a choice is necessary. A compromise solution -

  consists in balancing the optical requirement of weak bonds by the mechanical requirement of strong bonds by choosing a system having a high degree of strong ionic bonding. Compared to oxide glasses, the use of fluorides has a potential advantage due to the larger atomic weight of fluorine. It is also possible to obtain additional benefits by replacing some of the fluorine content with other halogens. Thus, for example, it has been found possible to perform a partial substitution with iodine by adding iodine to the melt. Nevertheless, in this general context, it should be noted that if we consider the heavier anions it becomes

  more and more difficult to form stable glasses.

  The following table lists the examples of glass compositions which have been manufactured and have been recognized as capable of producing glasses allowing good drawing of glass fibers from the surface of the molten glass without perceptible devitrification. From this it was concluded that the samples would probably be sufficiently stable to allow their use in the preparation of optical fibers.

  by the conventional technique of stretching from a crucible.

  TABLE Constituents expressed in molar percentage Example NO ZrF4 HfF4 ThF4 BaF2 CeF3 PbF2 MgF2 SrF2 CsF NaF LaF3

1 28.75 28.75 8.75 33.75

2 57.5 8.75 33.75

3 55 45

4 57.5 33.75 8.75

57.5 8.75 30.37 3.38

6 57.5 8.75 25.3 8.45

7 57.5 8.75 16.87 16.87

8 57.5 8.75 8.45 25.3

9 57.5 8.75 15.18 10.12 8.45

57.5 8.75 30.38 3.37

11 57.5 8.75 25.3 8.45

12 57.5 8.75 16.88 16.88

13 57.5 8.75 28.6 3.4 0.9 0.9

14 57.5 8.75 28.6 3.4 1.8

57.5 32.5 10

1'6 57.5 30 3.5 9

17 57.5 30 3.15 0.4 9

18 57.5 30 3.15 0.2 0.2 9

N N 0% ro

- 2 48 1262

  Glasses of this type can be made directly from

  of fluorides but given the relative cost of such fluorides.

  With respect to their oxides, it has been preferred to start from the oxides and to treat them by addition of ammonium bifluoride. Appropriate quantities of extremely pure oxides were mixed and the resulting mixture was put in a platinum or glassy carbon crucible and heated in air at 400 ° C. for one hour to convert the oxides to

  fluorides which are then heated to 8500 to form an infusion mixture.

  The latter is then poured into a mold.

  It is obvious that the foregoing description has been

  made by way of non-limiting example and other variants

  can be envisaged without departing from the scope of the invention.

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Claims (9)

  1. Fluoride-based glass for transmitting infrared radiation containing hafnium fluoride as the main formator   network and, in molar percentage, at least 40% in aggregates stabilized   network modifier, characterized in that the network stabilizer is present at least 5% molar percentage and consists of fluoride of one or more variable coordination elements other than hafnium, than the network consists of fluoride of one or more elements whose cations have a valence of one or two and an ionic radius at least equal to that of Sr + 2 or +2 Pb, and that the glass contains, in molar percentage, up to at 15% in aggregation of other compatible components, finally that one can optionally replace part of the fluoride content of the glass by a   equivalent molar percentage in aggregates of other halides.   2. Fluoride glass according to claim 1, characterized in that it is substantially free of zirconium fluoride. 3. Fluoride glass according to claim 1, characterized in that it is substantially free of other halides. than fluorides.   4. Fluoride glass according to claim 1 or 2, characterized   the fact that iodine is substituted for part of the content in fluorine.   5. Fluoride glass according to any one of the claims   1, 2 or 3, characterized in that the major constituent or the   The sole constituent of said network stabilizer is thorium fluride.   6. Fluoride glass according to any one of the claims   1, 2 or 3, characterized in that a constituent of said   Network stabilizer is lanthanum fluoride.   7. Fluoride glass according to any one of the claims   1, 2 or 3, characterized in that the major constituent or   the only constituent of said network modifier is barium fluoride.   8. Fluoride glass according to any one of the claims   1, 2 or 3, characterized in that said network modifier comprises lead fluoride and barium fluoride as a percentage 31t molar at least equal.   9. Optical fiber completely or partially composed of a glass   according to any one of claims 1 to 8.