Tunable Resonant Narrow-Band Filter Based on Electro-optic Materials
A resonant grating filter is a simple structure composed of a stack of a few dielectric layers on which a sub-wavelength grating is engraved. Their main interest is the narrow spectral FWHM they can achieve: in practice, quality factors greater than 7000 have already been obtained. The potential application fields are: optical telecommunications, spectroscopy, lasers, sensoring, etc. We aim to develop the potential of resonant grating filters by studying the tunability of their center wavelength by electro-optic effect. We chose two materials, Lithium Niobate and Barium Titanate, because of their large electrooptic coefficients. We developed a numerical tool based on the Fourier Modal Method including anisotropic materials. This is indispensable to analysis the effects related to the incident polarization. We compared several configurations, allowing a strong (up to 90nm) or weak tunability, independent or not versus the incident polarization. For each case, a physical interpretation is given for the facts that are observed. Last, we conclude by practical considerations concerning the feasibility of the structures and the influence of the absorption losses.