Effect of UV-induced birefringence on long-period-grating coupling characteristics

For the first time, an investigation into the effect of photoinduced birefringence on the coupling characteristics of long-period-gratings (LPGs) is presented. Current values of photoinduced birefringence are shown to be sufficient to induce the polarisation-dependent coupling of two components separated by ~23 nm into each cladding mode. Consequently, a major change in the coupling growth characteristics has been experimentally recorded during the photoinscription thereby avoiding total losses to the cladding modes