Chaos-assisted free-space coupling and transmission spectra of high-Q deformed microcavities

We investigate the mechanism of efficient excitation of high-Q modes in deformed microcavities via the chaos-assisted free-space coupling. A quantum scattering theory is employed to study the free-space transmission properties, from which the coupling strength can be derived. The theory predicts asymmetric Fano-like resonances around high-Q modes in background transmission spectra, which is in good agreement with previous experimental results. The phase shift occurring in the dynamical tunneling across Kolmogorov-Arnol'd-Moser tori is further studied, which plays a key role in the Fano-like resonance. This efficient free-space coupling holds potential advantages in simplifying experimental condition and exciting high-Q modes in higher-index-material microcavities.