Efficient visible wavelength mode switch based on mode-engineered ring resonator

Control of the transverse spatial modes of waveguides is critical for chip-scale wavefront shaping. These modes can be used to steer and structure light, which is required for quantum, portable display, and biological applications at visible wavelengths. However, it is challenging to efficiently excite higher-order modes at shorter wavelengths due to stringent phase-matching conditions and tight fabrication tolerances. Here, we demonstrate mode-engineered adiabatic ring resonators for efficient generation and control of the TE4 mode for the first time around 637 nm using thermo-optic phase tuning on a silicon nitride waveguide platform. We utilize a multistage transition to the higher-order mode, allowing for higher confinement within typical fabrication tolerances leading to low power and high-extinction ring modulation. This provides a viable path toward compact and high resolution beam shaping, structuring, and steering at visible wavelengths.