Multifunctional Metasurfaces : Design Principles and Device Realizations

In recent years, we have witnessed a rapid expansion of using super-thin metasurfaces to manipulate light or electromagnetic wave in a subwavelength scale. However, most designs are confined to a passive scheme and monofunctional operation, which hinders considerably the promising applications of the metasurfaces. Specifically, the tunable and multifunctional metasurfaces enable to facilitate switchable functionalities and multiple functionalities which are extremely essential and useful for integrated optics and microwaves, well alleviating aforementioned issues. In this book, we introduce our efforts in exploring the physics principles, design approaches, and numerical and experimental demonstrations on the fascinating functionalities realized. We start by introducing in Chapter 2 the "merging" scheme in constructing multi-functional metadevices, paying particular attention to its shortcomings issues. Having understood the merits and disadvantages of the "merging" scheme, we then introduce in Chapter 3 another approach to realize bifunctional metadevices under linearly polarized excitations, working in both reflection and transmission geometries or even in the full space. As a step further, we summarizes our efforts in Chapter 4 on making multifunctional devices under circularly polarized excitations, again including designing principles and devices fabrications/characterizations. Starting from Chapter 5, we turn to introduce our efforts on using the "active" scheme to construct multifunctional metadevices under linearly polarized wave operation. Chapter 6 further concentrates on how to employ the tunable strategy to achieve helicity/frequency controls of the circularly polarized waves in reflection geometry. We finally conclude this book in Chapter 7 by presenting our perspectives on future directions of metasurfaces and metadevices. Introduction 11 Early Attempts on Multifunctional Metasurfaces: The ``Merging'' Concept 17 Design Principles 17 Reflection-Geometry Realizations 17 Transmission-Geometry Realizations 20 Issues with the ``Merging'' Scheme 22 Multifunctional Metasurfaces/Metadevices Based on Single-Structure Meta-Atoms I: Linear-Polarization Excitations 23 Design Principles: Efficiency and Polarization Cross-Talk 23 Reflection-Geometry Realizations: Versatile Beam-Control Metadevices 25 Transmission-Geometry Realizations: Focusing and Beam Bending 42 Full-Space Wave-Control Multifunctional Metasurfaces 50 Concept and Meta-Atom Design of Full-Space Metasurface 52 Full-Space Beam Deflector 53 Full-Space Focusing Lens 59 Full-Space Bifunctional Metadevice 64 Summary 65 Multifunctional Metasurfaces/Metadevices Based on Single-Structure Meta-Atoms II: Circular-Polarization Excitations 69 Design Principles: Pancharatnam–Berry Phases 69 PB Metasurfaces in Reflection Geometry 71 PB Metasurfaces in Transmission Geometry 80 PB Metasurfaces in Full-Space Geometry 88 Concept and Meta-Atom Design 88 Bifunctional Meta-Lens 92 Bifunctional CP Beam Splitter 95 Summary 99 Linearly Polarized Active Multifunctional Metasurfaces 103 Design Principles: Role of Tunable Meta-Atoms on Phase Compensations 103 A Bifunctional Metadevice Exhibiting Anomalous-Reflection and Surface-Wave Conversion Functionalities 111 Aberration-Free and Functionality-Switchable Microwave Meta-Lenses 121 Summary 130 Circularly Polarized Active Multifunctional Metasurfaces 133 Design Principles 133 Dynamical Control on Helicity of Electromagnetic Waves 134 Tunable Pancharatnam–Berry metasurfaces 147 Summary 158 Conclusions and Perspectives 161 References 163 Authors' Biographies 185 Blank Page 2 Tunable and multifunctional metasurfaces facilitate switchable functionalities and multiple functionalities which are essential for integrated optics and microwaves. This book explores the physics principles, design approaches, and numerical and experimental demonstrations on the fascinating functionalities realized.