Optical Microring Resonators in Fluorine-Implanted Lithium Niobate for Electrooptical Switching and Filtering

We present a new approach for the fabrication of electrooptically tunable microring resonators in lithium niobate. Planar optical waveguides for vertical light confinement $(\Delta n_{ o} = 0.17)$ are produced by fluorine ion implantation. Optical microrings and bus waveguides are then formed by laser lithography masking and Ar$^{+}$ plasma etching. Electrodes are optically isolated from the optical microrings by a polyvinyl alcohol buffer layer with a high dielectric constant ($\varepsilon \sim 70$ at 10 Hz) to improve electrooptic tuning. The microrings with a radius of 80 $\mu$ m exhibit optical resonances with a modulation depth of 11 dB, a free spectral range of 2 nm, and an electrooptical tunability of 10 pm/V.