Origin of optical anisotropy in planar polymer waveguides

Many optical gas-sensor-devices utilise the optical anisotropy Delta N-eff (difference of effective mode indices) in a planar waveguide that may be in duced by molecule diffusion into the guiding film. The time dependence of D elta N-eff can be obtained in a dynamic waveguide experiment from the phase shift between two guided modes of different polarization. Different effect s of diffusing molecules on the guiding polymer film are discussed for isot ropic and anisotropic waveguide films. All effects on refractive indices an d film thickness have been studied additionally by the m-line spectroscopy in transmission. For the sensitive polyimide Ultradel(R) 9020D the origin o f the complicated anisotropy change is investigated. (C) 1998 Elsevier Scie nce S.A. All rights reserved.