Side-tunnel fibre: an approach to polarisation-maintaining optical waveguiding scheme

A new type of polarisation-maintaining fibre is proposed, analysed, and preliminary fabrication and measurement are described. The new fibre features two `side tunnels¿ bored on both sides of the core, and exhibits an absolutely single-polarisation characteristic or a relatively strong modal birefringence. The normalised birefringence obtained so far is 0.73×10¿4. This value is appreciably lower than expected. Two possible reasons are discussed.