Low-loss criterion for fused polarisation-maintaining fibre couplers

摘要

A simple low-loss criterion for polarisation-maintaining directional couplers made of fused tapered stress-induced birefringent fibres is proposed and used to explain the loss characteristics of some experimental couplers. It is shown that the very low excess loss of some experimental couplers is due to the combined use of index-matched stress-applying regions and a high core-cladding index difference.