Moisture Sensitivity of Holographic Gratings Recorded in Photosensitive Polyimide

Abstract

For the ultraviolet (UV) photosensitive polyimide Probimide\\circR 412 the dynamic behavior of induced refractive index changes due to indiffusion of water molecules is investigated by two different methods. On the one hand the optical waveguide anisotropy of thin films ( 2.41 µm) is determined in a transient experiment. On the other hand volume phase gratings in thick films ( 50–60 µm) are produced using holographic technique and the time dependence of the diffraction efficiency is monitored upon exposure to moisture. A crosslinking of the photosensitive polyimide can be achieved by UV illumination. Different sensitivities to moisture of exposed (crosslinked) and unexposed waveguide films are observed. This results in a change of the diffraction efficiency of a phase grating where exposed and unexposed regions alternate with each other. A simple model for the time dependence of the diffraction efficiency is presented and discussed.