Ultra-high Q alumina optical microresonators in the UV and blue bands

UV and visible photonics enable applications ranging from spectroscopic sensing to communication and quantum information processing. Photonics structures in these wavelength regimes, however, tend to experience higher loss than their IR counterpart. Particularly in the near-UV band, on-chip optical microresonators have not yet achieved a quality factor beyond 1 million. Here we report ultra-low-loss photonic waveguides and resonators patterned from alumina thin films prepared by a highly scalable atomic layer deposition process. We demonstrate ultra high Q factor of 1.5$\,\times\,$10$^6$ at 390nm, a record value at UV bands, and 1.9$\,\times\,$10$^6$ at 488.5nm.