| 摘要 |
An optical fibre device comprising an optical fibre coupler formed of two or more optical fibres fused together at a coupling region, at least a part of the coupling region being asymmetrical across its cross section. In summary, at least preferred embodiments of the invention provide a method of manufacturing polarisation insensitive couplers is achieved in asymmetric couplers by precisely controlling the cross-sectional shape. The shape required will depend on the extent of the dissimilarity between the input waveguides and possibly the size of the waveguide. The four-fold symmetry in the present couplers is broken either by the two input waveguides having different outer dimension and/or any other fibre parameter. The fibre parameters differing in the two input waveguides could be any of (a) outer cladding dimension, (b) cladding refractive index, (c) numerical aperture and (d) code dimension. A method of manufacturing an asymmetric coupler by progressive stretching, wherein the birefringence in the coupler resulting from the progressive stretching is substantially removed by precise control of the waist cross-sectional shape. Particular attention must be paid to the temperature distribution along the stretched region of glass in order to fabricate couplers with a uniform degree of fusion along their length. |
