Subwavelength-thick lenses with high numerical apertures and large efficiency based on high-contrast transmitarrays.

Amir Arbabi,Alexander J Ball,Andrei Faraon,Mahmood Bagheri,Yu Horie

doi:10.1038/ncomms8069

Amir Arbabi, Alexander J Ball + Show 3 more

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https://doi.org/10.1038/ncomms8069

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Abstract

Flat optical devices thinner than a wavelength promise to replace conventional free-space components for wavefront and polarization control. Transmissive flat lenses are particularly interesting for applications in imaging and on-chip optoelectronic integration. Several designs based on plasmonic metasurfaces, high-contrast transmitarrays and gratings have been recently implemented but have not provided a performance comparable to conventional curved lenses. Here we report polarization-insensitive, micron-thick, high-contrast transmitarray micro-lenses with focal spots as small as 0.57 λ. The measured focusing efficiency is up to 82%. A rigorous method for ultrathin lens design, and the trade-off between high efficiency and small spot size (or large numerical aperture) are discussed. The micro-lenses, composed of silicon nano-posts on glass, are fabricated in one lithographic step that could be performed with high-throughput photo or nanoimprint lithography, thus enabling widespread adoption.

Highlights

Flat optical devices thinner than a wavelength promise to replace conventional free-space components for wavefront and polarization control
Diffractive elements based on plasmonic metasurfaces composed of 2D arrays of ultrathin scatterers have attracted significant attention[6,7,8,9,10,11,12,13,14], but their efficiency is limited to 25% by fundamental limitations[15,16] and they suffer from material absorption[11]
The term high-contrast transmitarrays (HCTAs) is used when they are designed for large transmission

Summary

Introduction

Flat optical devices thinner than a wavelength promise to replace conventional free-space components for wavefront and polarization control. Several designs based on plasmonic metasurfaces, high-contrast transmitarrays and gratings have been recently implemented but have not provided a performance comparable to conventional curved lenses. We report polarization-insensitive, micron-thick, high-contrast transmitarray micro-lenses with focal spots as small as 0.57 l. A novel approach is to use high-contrast gratings (HCGs), fabricated from semiconductors or high refractive index (highindex) dielectrics[17,18,19], that can be designed with large reflection[20] or transmission[21] efficiencies. A promising class of aperiodic HCGs can be realized by positioning high-index dielectric scatterers on a periodic subwavelength 2D lattice. To demonstrate the HCTA versatility, we present design, simulation, fabrication and characterization results of polarization-insensitive high-NA micro-lenses with high focusing efficacy. The HCTA devices provide a more reliable alternative with fabrication techniques that lend themselves to wafer-scale processing

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