Trimming phase and birefringence errors in photosensitivity-locked planar optical circuits

A strong and stable photosensitivity response was permanently locked into hydrogen-loaded Mach-Zehnder planar waveguide circuits by 248-nm KrF-laser preirradiation. The photosensitivity enhancement survived thermal annealing up to 225 degreesC. Post-laser trimming at 248 nm induced an unsaturated refractive index increase of 0.002, and a birefringence change of Deltan similar to 0.0001. This combination of photosensitivity locking and post-laser tuning affords wide latitude for precise and stable tuning of waveguide phase errors and birefringence.