This paper describes the specially designed geometry of a dry-etched large-wedge-angle silica microdisk resonator that enables anomalous dispersion in the 780 nm wavelength regime. This anomalous dispersion occurs naturally without the use of a mode-hybridization technique to control the geometrical dispersion. By fabricating a 1-μm-thick silica microdisk with a wedge angle as large as 56° and an optical Q-factor larger than 107, we achieve a visible Kerr comb that covers the wavelength interval of 700–897 nm. The wide optical frequency range and the closeness to the clock transition at 698 nm of Sr87 atoms make our visible comb a potentially useful tool in optical atomic clock applications.

By overcoming fabrication limitations, we have successfully fabricated silica toroid microcavities with both large diameter (of 1.88 mm) and ultra-high-Q factor (of 3.3×108) for the first time, to the best of our knowledge. By employing these resonators, we have further demonstrated low-threshold Kerr frequency combs on a silicon chip, which allow us to obtain a repetition rate as low as 36 GHz. Such a low repetition rate frequency comb can now be directly measured through a commercialized optical-electronic detector.