Ultrahigh-Q, largely deformed microcavities coupled by a free-space laser beam

We experimentally report the fabrication of deformed silica microtoroids with only one-axial symmetry and very large deformation reaching 18%. The largely deformed microcavities are demonstrated to support ultrahigh-Q resonant modes exceeding 6 × 107, though much more chaos emerges compared with slightly deformed microcavities. The chaotic behavior of rays is beneficial to enhance dynamical tunneling to high-Q whispering-gallery modes, and therefore allows efficient coupling by a free-space laser beam. The largely deformed microcavities hold great potential in applied photonics and fundamental studies.