Two physical mechanisms for boosting the quality factor to cavity volume ratio of photonic crystal microcavities

We identify two physical mechanisms which drastically increase the Q/V factor of photonic crystal microcavities. Both mechanisms rely on a fine tuning the geometry of the holes around the cavity defect. The first mechanism relies on engineering the mirrors in order to reduce the out-of-plane far field radiation. The second mechanism is less intuitive and relies on a pure electromagnetism effect based on transient fields at the sub-wavelength scale, namely a recycling of the mirror losses by radiation modes. The recycling mechanism enables the design of high-performance microresonators with moderate requirements on the mirror reflectivity. Once the geometry around the defect is optimised, both mechanisms are shown to strongly impact the Q and the Purcell factors of the microcavity.