Pulley Couplers for Broadband Microcomb Generation in Si3N4 Ring Resonators

Abstract

Microresonator solitons enable high repetition-rate optical frequency combs. Their spectral span scales inversely with the strength of the resonator’s anomalous group velocity dispersion. In a thick (800 nm) silicon nitride platform, wide resonator waveguides (>2 µm) with weak anomalous dispersion are especially promising for the generation of broadband spectra. As wider waveguides have a weaker evanescent field, the coupling strength to their bus waveguide is reduced. To address this challenge, alternative coupler designs, such as pulley couplers are required. Here, we investigate pulley couplers for wide waveguide specifically targeted at broadband soliton generation. We observe significant improvement of the coupling ideality compared to conventional coupler geometries and broadband four-wave mixing spectra are observed in 2.8 µm wide microresonators.