Synthesis and Characterisation of Heavy Metal Fluoride Glasses and Fibres
- PDF / 431,685 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 9 Downloads / 201 Views
SYNTHESIS AND CHARACTERISATION OF HEAVY METAL FLUORIDE GLASSES AND FIBRES PAUL W FRANCE, S F CARTER, M W MOORE AND J R WILLIAMS British Telecom Research Laboratories Martlesham Heath Ipswich IP5 7RE U.K. ABSTRACT The fabrication of optical fibres based on fluoride glasses has required the development of novel preparation techniques. Some of these techniques are based on methods used to prepare multicomponent oxide glass fibres although some have been developed specially for fluoride glasses. This paper will review such processes as glove-box melting, reactive atmosphere processing, and rapid quenching; show how these have been used to prepare fluoride glass fibres with losses down to 2.6 dB/km at 2.6 'um; and discuss remaining problems with the glass. INTRODUCTION The first fluorozirconate glasses, discovered at the University of Rennes [1], were synthesised using fairly simple techniques. Although they were of reasonable quality, it soon became apparent that the much higher qualities needed for the fabrication of optical fibres would require new techniques to be developed. Several years on some of the particular problems with melting these glasses have been studied in more detail. Particular considerations are melting environments, containment vessels, homogenisation, fining and crystallisation; and new processes to overcome these problems have been implemented in the synthesis. Some of these processes are discussed here, and shown how they can be used to melt fluoride glasses and fibres. In addition the characterisation of the fibre and individual scattering centres is also discussed with a view to eliminating remaining problems. GLASS SYNTHESIS Numerous techniques have now been reported for the synthesis of HMF glasses. They include CVD (chemical vapour deposition) and melting processes, but without question the most successful technique to date is melting. A typical melting arrangement is shown in Fig. 1 and we continue with a discussion of this process. Melting Environments The melting techniques developed for oxide glasses are generally unsuitable for fluoride systems. Firstly the materials are often toxic and secondly they may hydrate to a certain extent at room temperature. For these reasons the materials should be stored and handled under dry inert conditions, such as Ar or N2 , usually in specially designed glove boxes. A further problem is possible hydrolysis of the melt at higher temperatures, leading to a severe OH- contamination, according to the reaction: [F'](m) + H20(g) --- [OH'](m) + HF(g)
...
Mat. Res. Soc. Symp. Proc. Vol. 172. ©1990 Materials Research Society
(1)
136
Hence melting also requires a controlled dry atmosphere, and this is generally provided by melting in separate glove boxes or in sealed liners, as shown in Fig. 1, and flushed with dry gas such as Ar or N2 . Merely providing an extremely dry melting environment should lead to very low OH- contamination since at high temperatures OH- in the melt should be liberated as HF according to: OH'(m) + F'(m) _
02"(m) + HF(g)
..
(2)
Data Loading...
