High-Q photonic nanocavity in a two-dimensional photonic crystal

Photonic cavities that strongly confine light are finding applications in many areas of physics and engineering, including coherent electron–photon interactions1, ultra-small filters2,3, low-threshold lasers4, photonic chips5, nonlinear optics6 and quantum information processing7. Critical for these applications is the realization of a cavity with both high quality factor, Q, and small modal volume, V. The ratio Q/V determines the strength of the various cavity interactions, and an ultra-small cavity enables large-scale integration and single-mode operation for a broad range of wavelengths. However, a high-Q cavity of optical wavelength size is difficult to fabricate, as radiation loss increases in inverse proportion to cavity size. With the exception of a few recent theoretical studies8,9,10, definitive theories and experiments for creating high-Q nanocavities have not been extensively investigated. Here we use a silicon-based two-dimensional photonic-crystal slab to fabricate a nanocavity with Q = 45,000 and V = 7.0 × 10-14 cm3; the value of Q/V is 10–100 times larger than in previous studies4,11,12,13,14. Underlying this development is the realization that light should be confined gently in order to be confined strongly. Integration with other photonic elements is straightforward, and a large free spectral range of 100 nm has been demonstrated.