Sr1.8Ca0.2NaNb5O15 films for electro-optic modulator application

Ferroelectric Sr1.8Ca0.2NaNb5O15 ( SCNN) optical thin films have been fabricated on fused quartz substrates using pulsed laser deposition. X-ray diffraction measurements and scanning electron microscopy revealed that these SCNN thin films exhibited a pure tetragonal tungsten-bronze phase polycrystalline crystal structure with good surface morphologies. Their transmittance profiles showed that the films had a transmittance of 80% in the visible range. The optical waveguiding properties of the films were characterized using a coupled prism technique. Distinct m-lines of the guided transverse-electric (TE) and -magnetic (TM) modes of the SCNN waveguides were observed. The TE and TM refractive indices were found to be 2.251 and 2.237, respectively. A simple, direct and reliable technique based on the shift of synchronous angles of the guided modes as a function of the applied electric field was used to investigate the effective electro-optic coefficient, which was determined to be 176.6 pm V-1. We demonstrate that this technique is convenient in studying the effective electro-optics properties for thin films.