Efficient and wavelength-tunable second-harmonic generation towards the green gap

Achieving compact and efficient visible laser sources is crucial for a
wide range of applications. However traditional semiconductor laser
technology faces difficulties in producing high-brightness green light,
leaving a “green gap” in wavelength coverage. Second-harmonic generation
(SHG) offers a promising alternative by converting near-infrared sources
to visible wavelengths with high efficiency and spectral purity. Here, we
demonstrate efficient and tunable SHG within the green spectrum using a
high-Q Si3N4 microresonator On chip green power as high as 5.3 mW is
generated with a conversion efficiency of 141%/W (absolute 7.9%). A
space-charge grating induced by the photogalvanic effect realizes
reconfigurable grating numbers and flexible wavelength tuning over a range
of 2.6 THz. Additionally, grating formation dynamics and competition is
observed. These findings underscore the potential of Si3N4 as a robust,
integrative platform for on-chip, tunable green light sources.