Single-polarisation characteristics of doubly clad type nonconfocal elliptic fibres

The paper gives single-polarisation characteristics of doubly clad type nonconfocal elliptic fibres. The outside layer of the core is composed of a nonconfocal elliptical layer. Two types of cross-section are studied: type 1 fibre, where the major axis of the core equals the major axis of the pit; and type 2 fibre, where the minor axis of the core equals the minor axis of the pit. Numerical analyses are investigated to satisfy simultaneously the larger modal birefringence, the larger singlepolarisation bandwidth, the smaller dispersion sensitivity, the larger power concentration in the core, and the zero total dispersion within the single-mode region. When satisfying zero total dispersion at the wavelength of 1.55 (mu)m, it is found that: (i) for type 1 fibre, the maximum modal birefringence of 3.62 * 10 ^ (-3) and the maximum single-polarisation bandwidth of 138.5 nm are attained while keeping the power in the core more than 94%. however, the very large relative index difference of 3.69% is required; (ii) for type 2 fibre, the maximum single-polarisation bandwidth of 111.9 nm is attained within the practical relative index difference of < 0.53% while keeping the power in the core > 82%, whereas the modal birefringence becomes small.