A polarization independent optical waveguide structure has been developed and optimized towards minimized dependence on deviations in the processing parameters and very low processing complexity. The tolerance analysis was based on typical parameters of the silicon oxynitride technology. The optimized waveguide structure meets the criterion of a channel birefringence within 5x10-5 taking the processing tolerance into account. Moreover, it was found that the channel birefringence is thickness independent (within the 10-5 criterion) over a range of up to 200 nm. The optimized waveguide, fulfilling also the remaining demands of the application, has been applied for the realization of a passband flattened add-drop multiplexing device with 0.4 nm free spectral range and 0.03 nm TE-TM shift
