Manipulating Light With Multifunctional Metasurfaces

Abstract

In free space, electromagnetic waves are solutions of Maxwell's wave equation. A monochromatic electromagnetic wave is characterized by its frequency, its amplitude and phase, its direction of propagation and its polarization state. Accordingly, to control the flow of light - either to steer a laser beam, to form an image, or to excite an atom in a specific way - requires the ability to manipulate these electromagnetic degrees of freedom across the wavefront. However, the set of available functions from conventional optical elements is rather limited. Recently, metasurfaces - ultrathin planar photonic components consisting of subwavelength-spaced nanostructures - have emerged as a versatile platform for wavefront shaping. This thesis explores how to manipulate the various degrees of freedom of light using multifunctional metasurfaces. By engineering the interaction of light with specially designed nanostructures, we demonstrated metasurfaces with tailored spatial, spectral, angular and polarization responses. In particular, we developed new dispersion engineering strategies for wavelength-controllable beam shaping; studied the interplay of the angular and polarization degrees of freedom using freeform metasurfaces; and last but not least, utilized spatially-interleaved metasurfaces to enable new methods of efficient depth sensing. These results have expanded the scope of multifunctional wavefront control techniques, and opened up possibilities for various applications in science and technology.