Tutorial on metalenses for advanced flat optics: Design, fabrication, and critical considerations

Metalenses comprised of artificial subwavelength structures known as meta-atoms have demonstrated abilities beyond conventional bulky optical components by modulating the phase, amplitude, and polarization of light in an ultrathin planar form factor. In this Tutorial, we present the fundamental principles and practical design procedures to exploit the abilities of metalenses, including achromaticity, high numerical aperture, and tunability. The fundamental principles include both plasmonic and dielectric meta-atoms, which require different physics to describe their light-matter interactions. In the phase modulation section, we compare the methods of physically implementing phase via meta-atoms including both the propagation and geometric phase methods. Next, we cover the recent progress of nanofabrication procedures from the perspective of the metalenses using materials such as titanium dioxide, gallium nitride, and hydrogenated amorphous silicon. We further compare the various fabrication methods with regard to the resolution, size, cost, and optical properties of fabricated metalenses. Then, we describe the critical considerations of metalenses including aberration-correction, numerical aperture, and tunability for advanced flat optics. Herein, we provide a practical guide for the design, fabrication, and critical considerations of metalenses with examples of research from early works to more recent developments.