  High coherence visible and near-visible laser sources are centrally important
to the operation of advanced position/navigation/timing systems as well as
classical/quantum sensing systems. However, the complexity and size of these
bench-top lasers is an impediment to their transitioning beyond the laboratory.
Here, a system-on-a-chip that emits high-coherence visible and near-visible
lightwaves is demonstrated. The devices rely upon a new approach wherein
wavelength conversion and coherence increase by self-injection-locking are
combined within in a single nonlinear resonator. This simplified approach is
demonstrated in a hybridly-integrated device and provides a short-term
linewidth around 10-30 kHz. On-chip, converted optical power over 2 mW is also
obtained. Moreover, measurements show that heterogeneous integration can result
in conversion efficiency higher than 25% with output power over 11 mW. Because
the approach uses mature III-V pump lasers in combination with thin-film
lithium niobate, it can be scaled for low-cost manufacturing of high-coherence
visible emitters. Also, the coherence generation process can be transferred to
other frequency conversion processes including optical parametric oscillation,
sum/difference frequency generation, and third-harmonic generation.
