Design considerations for circularly form-birefringent optical fibres

Single-lobe and multiple-lobe single-mode fibre core structures which are twisted at a uniform rate along the fibre axis are proposed as candidates for achieving very high circular birefringence in optical fibres. The main characteristics of these structures are analysed in general terms using ray optics. These circularly birefringent fibres can give 100% twisting efficiency without any linear birefringence effects. Even with parameters similar to conventional monomode fibres, the maximum obtainable birefringence can be a few rotations/mm.