Multifunctional Metasurfaces: Design Principles and Device Realizations

Introduction
Early Attempts on Multifunctional Metasurfaces: The ``Merging\'\' Concept
	Design Principles
	Reflection-Geometry Realizations
	Transmission-Geometry Realizations
	Issues with the ``Merging\'\' Scheme
Multifunctional Metasurfaces/Metadevices Based on Single-Structure Meta-Atoms I: Linear-Polarization Excitations
	Design Principles: Efficiency and Polarization Cross-Talk
	Reflection-Geometry Realizations: Versatile Beam-Control Metadevices
	Transmission-Geometry Realizations: Focusing and Beam Bending
	Full-Space Wave-Control Multifunctional Metasurfaces
		Concept and Meta-Atom Design of Full-Space Metasurface
		Full-Space Beam Deflector
		Full-Space Focusing Lens
		Full-Space Bifunctional Metadevice
	Summary
Multifunctional Metasurfaces/Metadevices Based on Single-Structure Meta-Atoms II: Circular-Polarization Excitations
	Design Principles: Pancharatnam–Berry Phases
	PB Metasurfaces in Reflection Geometry
	PB Metasurfaces in Transmission Geometry
	PB Metasurfaces in Full-Space Geometry
		Concept and Meta-Atom Design
		Bifunctional Meta-Lens
		Bifunctional CP Beam Splitter
	Summary
Linearly Polarized Active Multifunctional Metasurfaces
	Design Principles: Role of Tunable Meta-Atoms on Phase Compensations
	A Bifunctional Metadevice Exhibiting Anomalous-Reflection and Surface-Wave Conversion Functionalities
	Aberration-Free and Functionality-Switchable Microwave Meta-Lenses
	Summary
Circularly Polarized Active Multifunctional Metasurfaces
	Design Principles
	Dynamical Control on Helicity of Electromagnetic Waves
	Tunable Pancharatnam–Berry metasurfaces
	Summary
Conclusions and Perspectives
References
Authors\' Biographies
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