Periodic bumps in miniature racetrack for light converts near-IR laser into specific desired wavelengths of visible light

https://phys.org/news/2023-11-scientists-miniaturized-technique-generate-precise.html

"select wavelength to accuracy of 99.7%. With improvements, >99.9%, required for powering high-precision optics such as atomic clocks, quantum information ... transforms near-IR laser into specific wavelength of visible light (plus unused longer wavelength). These OPO-generated colors, unlike those previously created by smooth microrings, can be precisely controlled by bumps' spacing and width... shift towards longer or shorter wavelength depending on shift magnitude which is determined by bump height"