[Paper Review] Dielectric Metasurfaces for Complete and Independent Control of Optical Amplitude and Phase

Adam Overvig, Sajan Shrestha+5 more|arXiv (Cornell University)|Mar 1, 2019

Metamaterials and Metasurfaces Applications48 references475 citations

TL;DR

This paper presents a dielectric metasurface platform that enables complete, independent control of optical amplitude and phase at one or two frequencies using structurally birefringent meta-atoms with tunable form birefringence and in-plane rotation. The approach achieves high-efficiency, artifact-free holography by simultaneously modulating both amplitude and phase, enabling high-fidelity 2D and 3D holographic imaging without iterative algorithms.

ABSTRACT

Metasurfaces are optically thin metamaterials that promise complete control of the wavefront of light but are primarily used to control only the phase of light. Here, we present an approach, simple in concept and in practice, that uses meta-atoms with a varying degree of form birefringence and rotation angles to create high-efficiency dielectric metasurfaces that control both the optical amplitude and phase at one or two frequencies. This opens up applications in computer-generated holography, allowing faithful reproduction of both the phase and amplitude of a target holographic scene without the iterative algorithms required in phase-only holography. We demonstrate all-dielectric metasurface holograms with independent and complete control of the amplitude and phase at up to two optical frequencies simultaneously to generate two- and three-dimensional holographic objects. We show that phase-amplitude metasurfaces enable a few features not attainable in phase-only holography; these include creating artifact-free two-dimensional holographic images, encoding phase and amplitude profiles separately at the object plane, encoding intensity profiles at the metasurface and object planes separately, and controlling the surface textures of three-dimensional holographic objects.

Motivation & Objective

• To overcome the limitation of conventional phase-only metasurfaces that cannot independently control amplitude and phase.
• To develop a CMOS-compatible, all-dielectric metasurface platform capable of simultaneous and independent control of amplitude and phase at one or two optical frequencies.
• To demonstrate high-fidelity, artifact-free computer-generated holography without iterative optimization algorithms.
• To enable new holographic functionalities such as separate encoding of phase and amplitude profiles, intensity control at both metasurface and object planes, and textured 3D holographic objects.

Proposed method

• Utilizes structurally birefringent dielectric meta-atoms to control amplitude via conversion efficiency of circularly polarized light between opposite handednesses.
• Employs geometric (Pancharatnam-Berry) phase by rotating the in-plane orientation of meta-atoms to control the output phase of transmitted light.
• Models the system using Jones calculus, where the transmission matrix combines amplitude (A_o, A_e) and phase (ϕ_o, ϕ_e) responses along ordinary and extraordinary axes.
• Designs meta-atoms with height d and effective refractive indices n_o, n_e to achieve desired phase shifts via ϕ_o,e = k₀n_o,e d.
• Employs a two-frequency design by engineering structural dispersion to achieve independent amplitude and phase control at two distinct wavelengths.
• Uses non-iterative, direct synthesis of complex transmission functions to generate holograms, avoiding the convergence issues of Gerchberg-Saxton algorithms.

Experimental results

Research questions

• RQ1 Can dielectric metasurfaces achieve independent and complete control of both amplitude and phase at optical frequencies?
• RQ2 Can this dual-control platform enable artifact-free holographic imaging without iterative phase retrieval algorithms?
• RQ3 What new holographic functionalities become accessible with independent amplitude and phase control, such as separate encoding at object and metasurface planes?
• RQ4 How does the performance of phase-amplitude holography compare to phase-only holography in terms of image fidelity and efficiency?
• RQ5 Can the platform simultaneously control amplitude and phase at two distinct optical frequencies for multiwavelength holography?

Key findings

• The metasurface platform achieves independent control of amplitude and phase using only two geometric degrees of freedom: form birefringence and in-plane rotation.
• Holograms generated with the phase-amplitude (PA) metasurface show no ringing artifacts or speckle noise, unlike phase-only (PO) holograms that require iterative GS algorithms and suffer from image degradation.
• The method enables high-fidelity 3D holographic objects with distinct surface textures, a capability not realizable with phase-only holography.
• The platform allows separate encoding of phase and amplitude profiles at the object plane, and independent control of intensity distributions at both the metasurface and object planes.
• The system achieves high efficiency with minimal RMS error, and the trade-off between image quality at the metasurface and object planes is analytically and experimentally validated.
• The approach is extended to dual-wavelength operation, enabling simultaneous control of amplitude and phase at two optical frequencies, demonstrating multi-color holography with independent tuning.