Single-polarisation single-mode optical fibre with refractive-index pits on both sides of core

A new refractive-index distribution for realising a single-polarisation single-mode optical fibre is proposed. This distribution features two pits, on either side of the core. The propagation characteristics are calculated by the two-dimensional finite-element method. The relative birefringence ¿ß/ßav is 1 ~ 2.5 × 10¿4 when core/cladding index difference is 1%.