Broadband Visible Wavelength Microcomb Generation In Silicon Nitride Microrings Through Air‐Clad Dispersion Engineering

Abstract The development of broadband microresonator frequency combs at visible wavelengths is pivotal for the advancement of compact and fieldable optical atomic clocks and spectroscopy systems. Yet, their realization necessitates resonators with anomalous dispersion, an arduous task due to the prevailing normal dispersion regime of materials within the visible spectrum. In this work, it is evinced that silicon nitride microring resonators with air cladding on top and sides—a deviation from the frequently employed silica‐embedded resonators—allows for the direct generation of broadband microcombs in the visible range. Combs pumped at 1060 nm (283 THz) are experimentally demonstrated that reach wavelengths as short as 680 nm (440 THz), and combs pumped at 780 nm (384 THz) reach wavelengths as short as 630 nm (475 THz). Simulations show that microcombs extending to wavelengths as low as 461 nm (650 THz) should be accessible in this platform.