Large electrooptic modulation using ferroelectric thin films in a Fabry-Perot cavity

We report a reflective thin film ferroelectric light modulator which has exhibited optical phase modulation as large as fifty degrees and on/off signal ratio of twenty for intensity modulation. The large optical modulation was achieved by means of multiple reflection. A ferroelectric (FE) PLZT thin film material, deposited on Pt-coated silicon substrate, was used as the modulating medium. An indium-tin oxide (ITO) thin layer was deposited on the ferroelectric films as the top electrode. A He-Ne laser beam was obliquely incident on the ITO/FE/Pt structure. The light modulation was detected in the laser beam reflected from the thin film structure when a voltage signal was applied to the ITO and Pt electrodes. Unlike transmission-mode modulators, the sandwich of the ferroelectric films between the air-ITO and FE-Pt interfaces exhibited characteristics of a Fabry-Perot etalon. Near a Fabry-Perot peak, drastically enhanced light modulation than transmission devices was obtained. Design principles and the performance of the modulator are discussed