Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Patent
1997-03-20
1998-06-30
Bonner, Melissa
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
501 40, 372 40, 372 6, 385142, 359343, 359341, C03C 332, C03C 400, C03C 1304, H01S 317
Patent
active
057729158
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to halide glass compositions.
2. Related Art
Halide glasses have been known since 1978 and, among other things, they have been recognised as potentially useful for specialised optical waveguides, e.g. optical fibres. In particular some halide glasses have been found to display favourable properties as hosts for lasing dopants, e.g. rare earth metals such as Er.sup.3+, Nd.sup.3+ and Pr.sup.3+. The lasing dopant is usually incorporated into the path region of a waveguide, e.g. the core of an optical fibre. An important end-use for the lasing glasses is as photonic amplifiers for telecommunications.
A wide range of halide glass compositions has been reported and the properties have been studied. It have been recognised that these glasses form good hosts for the rare earth elements as lasing species but the identification and selection of compositions having favourable properties remains difficult. In particular, the prior art has failed to identify glass compositions capable of lasing at 1300 nm with sufficient efficiency for use in telecommunications networks. This invention relates to compositions which have good properties.
It is now convenient to discuss the properties of the glass required in a lasing device such as a fibre amplifier. These properties will be considered under three different headings.
It is important that all glasses shall remain in the glass state, ie. they shall not devitrify under conditions of use. It is also important that the glasses shall not be subject to crystallisation which might be considered as incipient devitrification. In addition it is also necessary that the compositions shall be suitable for use in glass forming and further processing. In particular it is necessary that a composition be stable in the melt, that it shall be capable of withstanding practical cooling rates and the conditions necessary for fibre forming, eg. during the pulling of a fibre preform into a fibre. It will also be apparent that chemical stability of the various glass components is important, eg it is desirable to avoid water soluble ingredients and, even more important, to avoid hygroscopic ingredients.
Lasing devices usually include waveguiding structures and it is clearly important to avoid unnecessary attenuation of either the signal wavelength or the pump wavelength. The requirement for low attenuation means that it is desirable to avoid components which have unnecessarily high absorptions at wavelengths of interest. It is also necessary to avoid scatter which emphasises some of the fundamental glass properties, ie. that the glass shall not form crystals even on a small scale.
It also appears that there is interaction between the host glass and the lasing species. For example, the lasing species may undergo what is often called "non-radiative decay". This implies that the lasing species loses energy other than by the intended lasing transitions. Non-radiative decay represents a loss of energy and it is, therefore, an undesirable effect. It appears that the host glass may participate in non-radiative decay either in the sense that it may assist this undesired effect or help to inhibit it. Nevertheless, whatever the reason, it is established that the host glass can affect the efficiency of the lasing process and it is desirable to select the host so as to achieve good lasing efficiencies.
The hosting properties of the glass appear to have substantial effects upon the efficiency of a laser, eg. the ratio of signal power output to pump power input. This efficiency is of substantial importance in telecommunications because it may define the available gain of an amplifier. In experimental work, it is often convenient to utilise the lifetime of the excited state as a measure of the efficiency; the two quantities can be regarded as proportional to one another. In some theoretical papers it is considered that the multi-phonon absorption of the host affects the lifetime of the excited state and hence the efficiency of lasers
REFERENCES:
patent: 5346865 (1994-09-01), Aitken et al.
patent: 5351335 (1994-09-01), Ohishi et al.
patent: 5560868 (1996-10-01), Jordan et al.
Chemical Abstracts, vol. 109, No. 12, 19 Sep. 1988, Columbus, Ohio, US; abstract No. 97721r, p. 287, see abstract & JP,A,63 197 841 (Nippon Telegraph and Telephone Public Corp.) 12 May, 1988.
Jha Animesh
Jordan Wayne G.
Bonner Melissa
British Telecommunications public limited company
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