Optical-fiber-based measurement of an ultrasmall volume high-Q photonic crystal microcavity

A two-dimensional photonic crystal semiconductor microcavity with a quality factor $Q\ensuremath{\sim}40,000$ and a modal volume ${V}_{\mathrm{eff}}\ensuremath{\sim}0.9$ cubic wavelengths is demonstrated. A micron-scale optical fiber taper is used as a means to probe both the spectral and spatial properties of the cavity modes, allowing not only measurement of modal loss, but also the ability to ascertain the in-plane localization of the cavity modes. This simultaneous demonstration of high-$Q$ and ultrasmall ${V}_{\mathrm{eff}}$ in an optical microcavity is of potential interest in nonlinear optics, optoelectronics, and quantum optics, where the measured $Q$ and ${V}_{\mathrm{eff}}$ values could enable strong coupling to both atomic and quantum dot systems.