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 interactions(1), ultra-small filters(2,3), low-threshold lasers(4), photonic chips(5), nonlinear optics(6) and quantum information processing(7). 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 studies(8-10), 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 x 10(-14) cm(3); the value of Q/V is 10-100 times larger than in previous studies(4,11 - 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.