Birefringence and path length adjustment of silica-based waveguide using permanent heater trimming

A birefringence induction method involving thin film heaters to eliminate the polarisation dependence of silica-based waveguides is proposed. The birefringence is adjusted by applying different electric powers to a single thin-film heater. This method was applied to a lattice-form filter and reduced the polarisation dependent frequency shift (PD-f) to less than 0.9% of the frequency period.