Molecular Crystals and Liquid Crystals Science and Technology Section B: Nonlinear Optics

Electro-optic measurements of poled polymeric films


Second order optical nonlinearities of poled polymeric films containing optically nonlinear chromophores can be measured either by second harmonic generation in a Maker fringe experiment or by the change in refractive index induced by an electric field in an electro-optic experiment. Theoretically the results of these two types of experiments are related, but experimentally, this has been observed to be only approximately true because of frequent occurrence of some resonance enhancement at the second harmonic wavelength. Electro-optic experiments at wavelengths having little or no absorption lead, in our opinion, to a more reliable way to measure the optical nonlinearity of these poled polymeric thin film structures. This is especially important for modulation and switching applications. Some common methods, which we have used for the determination of the electro-optic coefficient, are attenuated total reflection (ATR), ellipsometric reflection, Mach-Zehnder interferometry and the modulation index in an electro-optic phase modulator. Fabry-Perot cavity transmission or reflection has been applied by others. A comparison of these experimental methods will be given.