Roughly described, an optical device has first and second waveguide segments which are constructed such that irradiation changes both average refractive index and also birefringence in the respective segment. The change in birefringence as a function of the change in average refractive index, is different for the two segments. Predetermined lengths of each of the two segments are irradiated. In an MZI, the technique can be used to adjust simultaneously for one or more of differential path length phase delays, coupler-induced phase errors, and frequency errors.