Ultrasmall Mode Volumes in Dielectric Optical Microcavities

Abstract

We theoretically demonstrate a mechanism for reduction of mode volume in high index contrast optical microcavities to below a cubic half wavelength. We show that by using dielectric discontinuities with subwavelength dimensions as a means of local field enhancement, the effective mode volume ($V_{\mathrm{eff}}$) becomes wavelength independent. Cavities with $V_{\mathrm{eff}}$ on the order of ${10}^{-2}(\lambda /2n{)}^{-3}$ can be achieved using such discontinuities, with a corresponding increase in the Purcell factor of nearly 2 orders of magnitude relative to previously demonstrated high index photonic crystal cavities.