Investigations of LiNbO3 waveguides using the non-standard Z-propagation are presented. Due to the isotropic refractive index of the bulk material and a small residual TE/TM modal birefringence, this orientation seems to be well suited for passive, polarization-insensitive devices with increased power handling capability. The measured wavelength response curves of BOA-type wavelength multiplexers, fabricated with Z-propagating waveguides on X-cut LiNb01, however, indicate the presence of increased waveguide birefringence. This results in an opposite shift of the sinusoidal TE/TM transmission curves of nearly 180Ã‚Â°, which can not be verified by theoretical calculations (device simulation by the beam propagation method BPM ). The determination of the refractive index profile by m-line spectroscopy leads to gaussian profiles with polarization dependent 1/e-widths and maximum index increases An. BPM-simulations based on these profiles show results, which correspond well to the measurements.