Mid-Infrared Waveguide-Integrated Dielectric Metalens by Bigradient Slots on Silicon

This paper reports a waveguide-integrated bigradient dielectric metalens with a footprint of only 16.8×10 µm2. In mid-infrared wavelengths of 3.65-3.8 um, the metalens achieves high-efficiency in-plane focusing with the highest ratio of wavelength to focal length/spot size (0.268 & 2.83). After subsequent optimization and design, the total area of the bigradient metalens has been further compressed to 55.1% and demonstrated mode conversion applications and beam steering. This provides focusing components for the next generation of mid-infrared photonic integration, which also holds the potential for spectroscopic sensing, communication, neuromorphic computing, and non-linear optics.