  Frequency combs have applications that extend from the ultra-violet into the
mid-infrared bands. Microcombs, a miniature and often semiconductor-chip-based
device, can potentially access most of these applications, but are currently
more limited in spectral reach. Here, we demonstrate mode-locked silica
microcombs with emission near the edge of the visible spectrum. By using both
geometrical and mode-hybridization dispersion control, devices are engineered
for soliton generation while also maintaining optical $Q$ factors as high as 80
million. Electronics-bandwidth-compatible (20 GHz) soliton mode locking is
achieved with low pumping powers (parametric oscillation threshold powers as
low as 5.4 mW). These are the shortest wavelength soliton microcombs
demonstrated to date and could be used in miniature optical clocks. The results
should also extend to visible and potentially ultra-violet bands.
