Patent
1982-04-19
1984-12-25
Lee, John
G02B 726
Patent
active
044900066
DESCRIPTION:
BRIEF SUMMARY
The invention relates to improved connecting means for optical fibres, permitting them to be simply connected to each other or to an emitter or receiver of optical radiation.
For some time it has been clear that optical fibres will be an important competitor of electrical conductors as regards the transmission of information, especially since they have a very high signal capacity thanks to the possibility of working with high electromagnetic frequencies.
An optical fibre of the type in question functions as a wave guide for optical radiation. A so-called step index fibre consists of a core of glass or quartz with a high index of refraction and a surrounding jacket of glass or plastic with a lower index of refraction than that of the core. In a variant of this step index fibre, the so-called gradient index fibre, the index of refraction of the core varies continuously from high at the axis of the core to low at the edge of the core. For production reasons, this core is also surrounded by a glass-like jacket. For protection against mechanical damage, a practically usable fibre cable has also been provided on the outside with a number of layers of plastic material. To date, there is no standard for fibre diameters, but at present two especially advantageous types are available with regard to transmission characteristics and dimensions. One type of step index fibre has a core diameter of 100 .mu.m and a jacket diameter of 140 .mu.m. A suggested standard for gradient index fibre has a core diameter of 50 .mu.m and a jacket diameter of 125 .mu.m.
The problems involved in connecting such fibres are described in detail in applicant's patent applications 8003467-1 and 8003509-0.
By way of summary, it can be noted that the problem of jointing with connectors is to minimize optical radiation losses, preferably to less than 1 dB per joint. This means that a detachable connector must be able to achieve centering between two fibres within 5 .mu.m, for example, when the fibre core is about 50 .mu.m.
The solution used according to the above-mentioned patent applications is based on arranging a fibre in a holder directly in the centre of an external conical surface, two such holders being simply fitted to each other by means of an intermediate piece which has two coaxial internal conical surfaces opening in either direction.
The present invention addresses itself to the problem of mounting a fibre with satisfactory precision so that it is disposed on the axis of an external conical surface in such a connector member. The connector member is designed to be so functionally simple that it can meet military requirements for shock and temperature, i.e., -55.degree. to +125.degree. C.
Previous attempts have been made to centre fibres in mountings although not built on the conical principle, but these have encountered certain problems. In a known arrangement, inside a connector piece with an external fitting surface, a centered hole is arranged with an interior conical surface against which centering is achieved by means of three precision-made balls surrounding the fibre. One difficulty is that, although the balls guarantee a good adaption to the conical axis of the connector piece, they do not guarantee that the fibre will be on the conical axis at the truncated connector end of the external cone, since there is a certain distance to the location where the balls centre the fibre. It is thus necessary to centre the fibre at one more location, which can be accomplished, for example, with balls against another conical surface. It is, however, difficult to guarantee that the fibre is straight, and the additional centering means involve extra costs and complications. It is desirable to avoid the use of "watchmaker" methods when connecting optical fibres, and it is preferable to achieve methods which are also suitable, as far as possible, under military field conditions and in inclement weather.
Swedish Patent Application No. 8003509-0 suggests centering via a special centering piece which can be removed and which, during curing of a
REFERENCES:
patent: 4087155 (1978-05-01), Deacon
patent: 4158476 (1979-06-01), McCartney
patent: 4181402 (1980-01-01), Borsuk et al.
patent: 4208093 (1980-06-01), Borsuk
patent: 4378145 (1983-03-01), Stancati et al.
patent: 4389091 (1983-06-01), Lidholt et al.
Lee John
Ullah Akm E.
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