Origin of optical anisotropy in planar polymer waveguides

Many optical gas-sensor-devices utilise the optical anisotropy ΔNeff (difference of effective mode indices) in a planar waveguide that may be induced by molecule diffusion into the guiding film. The time dependence of ΔNeff can be obtained in a dynamic waveguide experiment from the phase shift between two guided modes of different polarization. Different effects of diffusing molecules on the guiding polymer film are discussed for isotropic and anisotropic waveguide films. All effects on refractive indices and film thickness have been studied additionally by the m-line spectroscopy in transmission. For the sensitive polyimide Ultradel 9020D the origin of the complicated anisotropy change is investigated.