High numerical aperture RGB achromatic metalens in the visible
Sangwon Baek, Joohoon Kim, Yeseul Kim, Won Seok Cho, Trevon Badloe, Seong‐Won Moon, Junsuk Rho, Jong‐Lam Lee
Abstract
We theoretically and experimentally demonstrate an RGB achromatic metalens that operates concurrently at three visible wavelengths ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>450</mml:mn> </mml:mrow> </mml:math> , 532, and 700 nm) with a high numerical aperture of 0.87. The RGB metalens is designed by simple integration of metalens components with the spatial interleaving method. The simulated spatial interleaving metalens shows RGB achromatic operation with focusing efficiencies of 25.2%, 58.7%, and 66.4% at the wavelengths of 450, 532, and 700 nm, respectively. A 450 μm diameter metalens operating at three designated wavelengths is fabricated with low-loss hydrogenated amorphous silicon. The fabricated metalens has the measured focusing efficiencies of 5.9%, 11.3%, and 13.6% at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>450</mml:mn> </mml:mrow> </mml:math> , 532, and 700 nm, respectively. The Strehl ratios of 0.89, 0.88, and 0.82 are obtained at given wavelengths, which show a capability of diffraction-limited operation.