Highly Efficient Gradient Solid Immersion Lens with Large Numerical Aperture for Broadband Achromatic Deep Subwavelength Focusing and Magnified Far Field

Abstract Achromatic deep subwavelength lens with large numerical aperture (NA) is in urgent need in several fields, from optical imaging, photolithography, spectroscopy, nanophotonics to microwave engineering and sensing. However, the previous proposed approaches to achieve deep subwavelength lens suffer from severe chromatic aberrations, limited bandwidth, and limited efficiency. In this paper, enlightened by Maxwell's fish‐eye lens, a semicircular gradient solid immersion lens is proposed and manufactured by gradient isotropic dielectrics. Highly efficient (above 85%) achromatic (7–13 GHz) deep subwavelength focusing with full width at half maximum around 0.15λ and large NA of 2.4 as well as magnified far‐field radiation (4–12 GHz) with high recognition are achieved. Theoretical analysis reveals that electric field enhancement at the lens/air interface and magnification of high spatial frequency deep subwavelength information contribute to deep subwavelength focusing and magnified far‐field radiation, respectively. Measured results of near field and far field agree well with those of theoretical predictions, which makes the presented lens having the potential to be applied in deep subwavelength engineering systems.