Conformally Mapped Mikaelian Lens for Broadband Achromatic High Resolution Focusing

Focusing light into a tiny spot of high resolution is of significant importance in fields from imaging, photolithography to microwave engineering and sensing. However, most of the previous high resolution metalenses are constrained by their limited bandwidth and efficiency. In this paper, on the basis of Mikaelian lens derived from conformal transformation optics, a rectangular gradient refractive index lens with a relatively larger refractive index profile is put forward and manufactured by gradient isotropic dielectrics. Highly efficient (above 74%) broadband (7–14 GHz) achromatic high resolution focusing with full width at half maximum (FWHM) around 0.2λ as well as large numerical aperture (NA) of 2.04 has been accomplished. Measured results agree well with theoretical predictions, which makes the presented lens having a great potential to be employed in high resolution imaging systems.