ELECTRO-OPTIC TUNABLE FILTER

This letter describes a tunable optical filter that couples light energy between ordinary and extraordinary polarizations in a birefringent electro-optic crystal at the phase-matched wavelength by means of a spatially periodic dc electric field. The specific embodiment described here is a LiTaO3 platelet operating with transverse electric field and located between cross polarizers. Analogies to both the Solc birefringent filter and the Harris acousto-optic filter are cited. The electro-optic filter is tuned by varying the spatial period of the electric field via an array of separately addressable finger electrodes. We have demonstrated tunability from 4700 Å to 4.5 μm. Experimental results of transmittance versus applied voltage and of bandwidth versus pass wavelength agree well with theory. The flexibility of this type of electronic filter in allowing synthesis of arbitrary transfer functions through nonperiodic voltage distributions is emphasized.