Glass manufacturing – Processes – Forming product or preform from molten glass
Patent
1987-04-09
1988-11-29
Lindsay, Robert L.
Glass manufacturing
Processes
Forming product or preform from molten glass
65 182, 472163, C03B 37023
Patent
active
047879270
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the fabrication of fibres suitable for the transmission of optical radiation, that is, radiation of ultra-violet, visible and infra-red wavelengths.
The ability to introduce small amounts of impurity dopants, e.g. rare-earth or transition metal ions, into the core or cladding of an optical fibre is useful for a number of reasons.
The fabrication of optical fibre amplifiers or lasers using for example neodymium or erbium as the impurity dopant is possible. An example of a neodymium fibre laser is described in our copending United Kingdom Patent Application No. 8520301.
The incorporation of, for instance, Terbium ions (Tb.sup.3+) into the silica glass matrix is well known to increase the Verdet constant of the glass and this is an advantage for fibre devices or sensors which interact with magnetic fields.
A distributed temperature sensor may be constructed which utilises temperature-dependent changes in either the absorption spectrum or fluorescence decay-time of a rare-earth or transition metal ion, e.g. Nd.sup.3+ or Cr.sup.3+, to indicate the temperature of the medium surrounding the fibre.
The introduction of, for instance, Nb.sup.3+ ions into the silica glass matrix is known to increase both the Kerr effect and the non-linear optical coefficients of the glass.
The introduction of certain ions, e.g. Cerium, into the glass allows the construction of scintillation counters by converting the energy of an incident high-energy particle or beam to an optical signal which propagates within the fibre.
We have devised a new fabrication technique which allows the fabrication of optical fibres containing controllable, low (<1 wt %) amounts of one or more impurity dopant ions in one or both of the core or cladding glass of an optical fibre. The technique permits the use of starting materials, e.g. rare-earth halides, which have a high melting point and hence have hitherto been unusable, since they exhibit a very-low vapour pressure at the temperatures commonly encountered in reactant delivery systems for optical fibre fabrication. This temperature is usually limited to around 250.degree. C., at which temperature the PTFE components used in the rotating seal connecting the deposition tube to the reactant delivery system begin to deform. Our process is also applicable to liquids which have a low vapour pressure at low temperatures (<250.degree. C.).
The impurity dopant(s) introduced into the glass using the technique may themselves create the refractive-index difference(s) required for the fibre to guide light. Alternatively, the index difference may be achieved in combination with commonly-used optical fibre dopants, such as for example, Boron trioxide, Fluorine, Germania, Phosphorous pentoxide and Titania. The technique is unique in that it allows the fabrication of long lengths of fibres containing, for instance, rare-earth ions, which have a relatively-high absorption in the visible
ear infra-red region, whilst substantially maintaining the low-loss properties of communications-grade fibres at other wavelengths.
According to the present invention, there is provided a method of fabricating a preform for the manufacture of optical fibres incorporating a doped glass characterised in that said method includes the sequential steps of depositing a dopant material in a dopant carrier chamber, heating the dopant within said chamber to cause said dopant to vaporise at a prdetermined rate, passing a gaseous source material through said carrier chamber to mix said dopant material with said source material, depositing from the mixture of said source material and said dopant material a mixture of solid components, and fusing said solid components to form a doped glass for said preform.
Preferably the method includes the sequential steps of chambers, the said dopants and, in the case of solid dopants, to fuse the said dopant(s) to the said chamber(s) walls, to vaporise at a predetermined rate whilst passing gaseous source materials through said carrier chamber(s) to mix said dopant material(s) wi
REFERENCES:
patent: 3971645 (1976-07-01), Bachmann
patent: 4067709 (1978-01-01), Stanton
patent: 4188089 (1980-02-01), Gliemeroth
patent: 4529427 (1985-07-01), French
patent: 4597787 (1986-07-01), Jacobson
Electronics Letters, vol. 21, No. 17, 15 Aug. 1985 (GB) S. B. Poole et al., "Fabrication of Low-Loss Optical Fibers Containing Rare-Earth Ion", pp. 737,738.
Japanese Journal of Applied Physics, vol. 22, No. 8, Aug. 1983, part 2, (Tokyo, JP) Seiko Mitachi: "Reduction of Impurities in Fluoride Glass Optical Fiber", pp. L537-L538.
Mears Robert J.
Payne David N.
Poole Simon B.
Reekie Laurence
Lindsay Robert L.
National Research Development Corporation
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