Optical Metasurfaces with Advanced Phase Control Functionalities

Abstract

The development of a metasurface platform with advanced micro- and nano-fabrication techniques has attracted a lot of attention. It exhibits a broad range of applications in the lens, hologram, image processing, vortex beam generation, information encoding, sensing, etc. Metasurfaces are ultrathin planar nanostructures made of subwavelength metallic or dielectric elements that can efficiently control the light characteristics such as polarisation, dispersion, amplitude, and phase. The high-index dielectric metasurfaces exhibit low loss and produce various types of resonant effects such as Mie-type resonances, Huygens' resonances, and so on. The Huygens' resonant regime of the dielectric metasurfaces exhibits the near-unity transmission window with a 2pi-phase coverage. The efficient 2pi-phase control capability with high transmittance feature makes the metasurfaces versatile tools for wavefront manipulation. The challenge is to realize the practical application of the metadevices such as beam deflection, optical image processing, sensing, hologram, lens, and so on. The performance of such metadevices can be made highly efficient by incorporating carefully engineered phase discretisation. Due to such engineered subwavelength wave discretisation, new functionalities that are not possible to date can be achieved by governing the phase response. In this thesis, I will first demonstrate the efficient control of deflection angle with high diffraction efficiency in the visible wavelength. I will also discuss deeply subwavelength metasurface resonators for terahertz wavefront manipulation. Then, I will focus on a novel dielectric resonant metagrating-based highly sensitive optical biosensing technique. Finally, I will demonstrate Mie-resonant dielectric metasurfaces can be used as a passive filter to perform image processing in the form of edge detection of a target object.