Electro-optical investigation of the dipole orientation in poled polymers

In order to exhibit low scattering losses and sufficiently large electro-optical or other nonlinear optical coefficients, polymers for active waveguide applications must be amorphous and contain molecular dipoles with large hyperpolarizabilities, respectively. Macroscopic effects are only possible if the dipoles have a poling-induced preferential orientation which is either uniform or suitably patterned within the optical guiding layer. Since the linear electro-optical or Pockels effect is one of the strongest and most useful effects in such poled polymers, it can also be employed for investigating the magnitude, the spatial distribution, and the stability of the dipole orientation. Novel and modified experimental techniques such as scanning electro-optical microscopy, electro-optical phase-shift interferometry and electro-optical thermal analysis are described. And typical results of such measurements are presented. It is demonstrated that the Pockels effect leads to experimental tools that are of similar value for investigating polar dielectric materials as those based on the quadratic electro-optical or Kerr effect.