Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1998-05-01
2001-10-09
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S126000, C385S115000, C065S409000, C065S411000
Reexamination Certificate
active
06301420
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical fibre having at least two cores for propagating radiation. The invention also relates to a method of making such a fibre.
2. Discussion of Prior Art
Optical fibres with two cores have been reported and applied to various problems in optical sensing and telecommunications. The potential of multicore fibres with more than two single-mode cores has also been recognized [S. Prasad: “Focusing light into a multiple-core fiber II application to ground-based interferometry”, Optics Communications 115 (1995) 368-378]. For example, bend sensing in the plane has been demonstrated using a four-core fibre, using a technique that can readily be extended to the monitoring of bending in three dimensions [M. J. Gander et al., “Bend measurements using multicore optical fiber”, presented at OFS 12 1997 ].
However, at present there are relatively few applications for multicore optical fibres. This is because it is very difficult to make multicore fibres with the required uniformity and geometrical accuracy. One way which has been reported is to use an extension of the process previously used to make two-core fibres. In this method, single-core preforms made by standard vapour-phase techniques are precisely machined and are then assembled to form a multicore preform. The multicore preform is then drawn into fibre [G. Le Noane et al., “Ultra high density cables using a new concept of bunched multicore monomode fibers: A key for future FTTH networks”, Proceedings of the International Wire & Cable Symposium (1994) 203-210]. This process, starting from a number of single core preforms, is a time-consuming and costly process. Furthermore, the addition of each extra core adds further complexity to the multicore preform. Higher multiplicity core fibres are therefore increasingly difficult to fabricate.
A single-mode photonic crystal fibre (PCF) is described by J. C. Knight et al., “All silica single-mode optical fiber with photonic crystal cladding”, Optics Letters 21 (1996) 1547-1549 and is of relevance to the present invention.
SUMMARY OF THE INVENTION
The present invention relates to a multicore optical fibre which can be made more easily than known multicore fibre and each core of which is capable of transmitting radiation in a single mode of propagation.
According to the present invention, a multicore optical fibre for transmitting radiation comprises;
two or more core regions, each core region comprising a substantially transparent core material and having a core refractive index, a core length, and a core diameter, wherein said core regions are arranged within a cladding region, said cladding region comprising a length of first substantially transparent cladding material, having a first refractive index, and wherein said first substantially transparent cladding material has an array of lengths of a second cladding material embedded along its length, wherein said second cladding material has a second refractive index which is less than said first refractive index,
such that radiation input to said fibre propagates along at least one of said core regions.
This provides an advantage over known multicore fibre in that, in the preform, the core regions may be automatically positioned in the precise geometry required without the need for accurate machining and assembly of single-core preforms. In addition, each core region may be single mode over a wide wavelength range.
The cladding region and the core regions may be arranged such that radiation input to the fibre propagates along at least one of the core regions in a single mode of propagation.
The first substantially transparent cladding material may have a substantially uniform first refractive index. One or more of the core materials may have a substantially uniform core refractive index. Each of the core regions may comprise the same core material. The first substantially transparent cladding material and the core materials may be substantially the same. In a preferred embodiment, at least one of the first substantially transparent cladding material and one of the core materials may be silica.
The array of lengths of the second cladding material may be an array of holes embedded along the length of the first substantially transparent cladding material. The holes may be a vacuum. Alternatively, the second cladding material may be air, liquid or a substantially transparent material. The substantially transparent core material of at least one of the core regions may comprise a dopant. At least one of the first or second cladding material may comprise a dopant. The second cladding material may comprise an amount of the first cladding material.
According to another aspect of the invention, a bend sensor comprises the multicore photonic crystal fibre of the present invention.
According to another aspect of the invention, a directional coupler comprises the multicore photonic crystal fibre of the present invention.
According to another aspect of the invention, a spectral filter comprises the multicore photonic crystal fibre of the present invention.
According to another aspect of the invention, a method of manufacturing a multicore optical fibre comprises the steps of;
(i) forming the fibre preform by arranging a plurality of composite rods in an array, each of said rods comprising a first substantially transparent cladding material, having a first refractive index, and each of said rods having a length, wherein said rods have an array of lengths of a second cladding material embedded along said rod lengths, wherein said second cladding material has a second refractive index which is less than said first refractive index,
(ii) arranging at least two rods comprising a substantially transparent core material within said fibre preform, and
(ii) drawing said fibre preform in fibre drawing apparatus to form said multicore optical fibre.
REFERENCES:
patent: 4300816 (1981-11-01), Snitzer et al.
patent: 5155792 (1992-10-01), Vali et al.
patent: 5321257 (1994-06-01), Danisch
patent: 5802236 (1998-09-01), DiGiovanni et al.
patent: 5805751 (1998-09-01), Kewitsch et al.
Birks et al., “Full 2-D Photonic Bandgaps in Silica/Air Structures”, Electronic Letters, vol. 31 (22), p. 1942 (Oct. 1995).
Birks Timothy A.
Greenaway Alan H.
Knight Jonathan C.
Lloyd Peter A.
Russell Philip S.
Nixon & Vanderhye P.C.
Sanghavi Hemang
The Secretary of State for Defence in Her Britannic Majesty&apos
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