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.