Metasurfaces are planar structures that locally modify the polarization, phase and amplitude of light in reflection or transmission, thus enabling lithographically patterned flat optical components with functionalities controlled by design. Transmissive metasurfaces are especially important, as most optical systems used in practice operate in transmission. Several types of transmissive metasurface have been realized, but with either low transmission efficiencies or limited control over polarization and phase. Here, we show a metasurface platform based on high-contrast dielectric elliptical nanoposts that provides complete control of polarization and phase with subwavelength spatial resolution and an experimentally measured efficiency ranging from 72% to 97%, depending on the exact design. Such complete control enables the realization of most free-space transmissive optical elements such as lenses, phase plates, wave plates, polarizers, beamsplitters, as well as polarization-switchable phase holograms and arbitrary vector beam generators using the same metamaterial platform.

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Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission

During the past few years, metasurfaces have been used to demonstrate optical elements and systems with capabilities that surpass those of conventional diffractive optics. Here, we review some of these recent developments, with a focus on dielectric structures for shaping optical wavefronts. We discuss the mechanisms for achieving steep phase gradients with high efficiency, simultaneous polarization and phase control, controlling the chromatic dispersion, and controlling the angular response. Then, we review applications in imaging, conformal optics, tunable devices, and optical systems. We conclude with an outlook on future potentials and challenges that need to be overcome.

https://www.degruyter.com/document/doi/10.1515/nanoph-2017-0129/pdf

A review of dielectric optical metasurfaces for wavefront control

A stacked array magnifier (SAM) forms a magnified, demagnified or unit image of an object. The SAM includes one or more non-refractive lenslet arrays and one or more refractive lenslet arrays to form a plurality of lenslet channels. Each lenslet channel has at least one refractive lenslet and at least one non-refractive lenslet. SAMs are combined and tiled to form a scaleable display of flat panel displays. Multiple SAMs are used to increase magnification selectively. Hybrid lenslet arrays of the invention are also useable for optical processing and non-imaging applications.

Lenslet array systems and methods

We report here on the theoretical performance of blazed binary diffractive elements composed of pillars carefully arranged on a two-dimensional grid whose period is smaller than the structural cutoff. These diffractive elements operate under unpolarized light. For a given grating geometry, the structural cutoff is a period value above which the grating no longer behaves like a homogeneous thin film. Because the grid period is smaller than this value, effective-medium theories can be fully exploited for the design, and straightforward procedures are obtained. The theoretical performance of the blazed binary elements is investigated through electromagnetic theories. It is found that these elements substantially outperform standard blazed echelette diffractive elements in the resonance domain. The increase in efficiency is explained by a decrease of the shadowing effect and by an unexpected sampling effect. The theoretical analysis is confirmed by experimental evidence obtained for a 3λ-period prismlike grating operating at 633 nm and for a 20°-off-axis diffractive lens operating at 860 nm.

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Design and fabrication of blazed binary diffractive elements with sampling periods smaller than the structural cutoff

The numerical aperture (NA) of a lens determines its ability to focus light and its resolving capability. Having a large NA is a very desirable quality for applications requiring small light–matter interaction volumes or large angular collections. Traditionally, a large NA lens based on light refraction requires precision bulk optics that ends up being expensive and is thus also a specialty item. In contrast, metasurfaces allow the lens designer to circumvent those issues producing high-NA lenses in an ultraflat fashion. However, so far, these have been limited to numerical apertures on the same order of magnitude as traditional optical components, with experimentally reported NA values of 0.99) and subwavelength thickness (∼λ/3), operating with unpolarized light at 715 nm. To demonstrate its imaging capability, the designed lens is appli...

A Metalens with a Near-Unity Numerical Aperture

: Multi-level diffractive phase have the potential to significantly improved the performance of many conventional lens systems. The theory, design and fabrication of these diffractive profiles are described in detail. Basic examples illustrate the potential usefulness, as well as the limitations, of these elements. Keywords: Binary optics; Diffractive optical elements.

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G. J. Swanson

Papers

Binary Optics Technology: The Theory and Design of Multi-Level Diffractive Optical Elements