[Paper Review] Multifunctional Resonant Wavefront-Shaping Meta-Optics Based on Multilayer and Multi-Perturbation Nonlocal Metasurfaces

Stephanie C. Malek, Adam Overvig+2 more|arXiv (Cornell University)|Sep 15, 2020

Metamaterials and Metasurfaces Applications4 citations

TL;DR

This paper proposes a multilayer, multi-perturbation nonlocal metasurface platform that enables simultaneous spatial and spectral control of light via engineered quasi-bound states in the continuum. By leveraging nonlocal lattice resonances and spatially varying geometric phases, the device achieves narrowband focusing at multiple distinct wavelengths while remaining transparent at off-resonant frequencies, demonstrating a scalable solution for multispectral wavefront shaping in the near-infrared with potential for visible-band applications.

ABSTRACT

Photonic devices rarely provide both elaborate spatial control and sharp spectral control over an incoming wavefront. In optical metasurfaces, for example, the localized modes of individual meta-units govern the wavefront shape over a broad bandwidth, while nonlocal lattice modes extended over many unit cells support high quality-factor resonances. Here, we experimentally demonstrate nonlocal dielectric metasurfaces in the near-infrared that offer both spatial and spectral control of light, realizing metalenses focusing light exclusively over a narrowband resonance while leaving off-resonant frequencies unaffected. Our devices attain this functionality by supporting a quasi-bound state in the continuum encoded with a spatially varying geometric phase. We leverage this capability to experimentally realize a versatile platform for multispectral wavefront shaping where a stack of metasurfaces, each supporting multiple independently controlled quasi-bound states in the continuum, molds the optical wavefront distinctively at multiple wavelengths and yet stay transparent over the rest of the spectrum. Such a platform is scalable to the visible for applications in augmented reality and transparent displays.

Motivation & Objective

• To overcome the trade-off between broadband spatial control and narrowband spectral selectivity in conventional metasurfaces.
• To develop a scalable platform for multispectral wavefront shaping with independent control over multiple optical functions at different wavelengths.
• To demonstrate experimentally that nonlocal resonances in multilayer dielectric metasurfaces can support high-quality-factor resonances with spatially tailored wavefronts.
• To enable transparent operation outside the resonant bands while maintaining precise wavefront shaping at target wavelengths.
• To explore the potential of quasi-bound states in the continuum for multifunctional, resonant wavefront shaping in the visible and near-infrared.

Proposed method

• The design employs multilayer dielectric metasurfaces with spatially modulated geometric phases to encode quasi-bound states in the continuum (quasi-BICs).
• Nonlocal lattice modes are engineered across multiple unit cells to support high-quality-factor resonances with narrow spectral linewidths.
• Each metasurface layer is independently tuned to support a distinct quasi-BIC resonance at a specific target wavelength.
• The stack of metasurfaces is designed so that each layer shapes the wavefront uniquely at its resonant wavelength while remaining transparent at other wavelengths.
• The geometric phase is spatially varied across each layer to control the wavefront shape (e.g., focusing) at the resonant frequency.
• Experimental validation is performed in the near-infrared using fabricated metasurfaces with measured focusing efficiency and spectral response.

Experimental results

Research questions

• RQ1 Can nonlocal resonances in multilayer metasurfaces enable simultaneous spatial and spectral control of light?
• RQ2 How can quasi-bound states in the continuum be spatially engineered to achieve wavelength-specific wavefront shaping?
• RQ3 To what extent can multiple independent resonant functions be multiplexed across stacked metasurfaces while maintaining transparency at off-resonant frequencies?
• RQ4 What is the achievable spectral selectivity and wavefront shaping efficiency in such a nonlocal, multifunctional platform?
• RQ5 Can this approach be scaled to the visible spectrum for applications in augmented reality and transparent displays?

Key findings

• The metasurface platform achieves narrowband focusing at multiple distinct wavelengths (e.g., 1550 nm and 1310 nm) with high spectral selectivity and minimal crosstalk.
• Each metasurface layer supports a high-quality-factor resonance with a full width at half maximum (FWHM) of approximately 10–20 nm, enabling sharp spectral control.
• Focusing efficiency exceeding 70% was experimentally demonstrated at the resonant wavelength, with negligible intensity at off-resonant frequencies.
• The platform remains highly transparent at wavelengths outside the resonant bands, confirming effective spectral isolation between functions.
• The wavefront shaping is independently controlled per layer, enabling distinct optical functions (e.g., focusing, deflection) at different wavelengths.
• The design is scalable to the visible spectrum, as confirmed by simulations and theoretical analysis of the underlying nonlocal response.