Photon confinement in photonic crystal nanocavities

The quest for enhanced light-matter interactions has enabled a tremendous increase in the performance of photonic-crystal nanoresonators in the past decade. State-of-the-art nanocavities now offer mode lifetime in the nanosecond range with confinement volumes of a few hundredths of a cubic micrometer. These results are certainly a consequence of the rapid development of fabrication techniques and modeling tools at micro- and nanometric scales. For future applications and developments, it is necessary to deeply understand the intrinsic physical quantities that govern the photon confinement in these cavities. We present a review of the different physical mechanisms at work in the photon confinement of almost all modern PhC cavity constructs. The approach relies on a Fabry-Perot picture and emphasizes three intrinsic quantities, the mirror reflectance, the mirror penetration depth and the defect-mode group velocity, which are often hidden by global analysis relying on an a posteriori analysis of the calculated cavity mode. The discussion also includes nanoresonator constructs, such as the important micropillar cavity, for which some subtle scattering mechanisms significantly alter the Fabry-Perot picture.