  Optical parametric oscillation (OPO) in a microresonator is promising as an
efficient and scalable approach to on-chip coherent visible light generation.
However, so far only red light at < 420 THz (near the edge of the visible band)
has been reported. In this work, we demonstrate on-chip OPO covering > 130 THz
of the visible spectrum, including red, orange, yellow, and green wavelengths.
In particular, using a pump laser that is scanned 5 THz in the near-infrared
from 386 THz to 391 THz, the signal is tuned from the near-infrared at 395 THz
to the visible at 528 THz, while the idler is tuned from the near-infrared at
378 THz to the infrared at 254 THz. The widest signal-idler separation we
demonstrate of 274 THz corresponds to more than an octave span and is the
widest demonstrated for a nanophotonic OPO to date. Our work is a clear
demonstration of how nonlinear nanophotonics can transform light from readily
accessible compact near-infrared lasers to targeted visible wavelengths of
interest, which is crucial for field-level deployment of spectroscopy and
metrology systems.
