Conformally Mapped Mikaelian Lens for Broadband Achromatic High Resolution Focusing

Abstract

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.

Spin-decoupled excitation and wavefront shaping of structured surface waves via on-chip terahertz metasurfaces

“…Therefore, when the LCP and RCP THz waves are normally incident on the meta-device, they can be converted to SBBs and SFBs, respectively. Then the ϕ res and ϕ geo values of each meta-atom can be derived from eqn (8).…”

“…Like propagating waves (PWs, freely traveling in space), surface waves (SWs) are another type of electromagnetic (EM) wave mode confined at metal/dielectric interfaces. 1 Due to the many unique properties of SWs, e.g., slow group velocity and local field confinement, a lot of extraordinary applications of SWs have been put forward, such as super-resolution imaging, 2 retroreflectors, 3 antennas, 4 second harmonic generation, 5 plasmonic vortex, 6 graded-index lenses, 7,8 spoof surface plasmon polariton switches, 29 and so on. Traditionally, prisms or gratings are used to excite and manipulate SWs.…”

Achromatic on-chip focusing of graphene plasmons for spatial inversions of broadband digital optical signals

“…To find the form of the function, we briefly turn our attention back to the well-known Mikaelian lens. The refractive index profile of Mikaelian lens, which can be extracted from Maxwell’s fish-eye lens by an exponential conformal mapping, exhibits a symmetrical distribution of n(x)=n0 sech(ξx), 43 , 44 , 48 as shown by the red curve in Fig. 2(a), where ξ is the gradient coefficient and n0 is the maximum refractive index at the central axis of the lens.…”

“…By studying the mode properties of the AGPPs supported by the GIWAL, we provide an analytical model to understand the complete physics underlying the on-chip focusing and other beam evolution behaviors, such as self-focusing, self-collimation, and pendulum effects of Gaussian beams as well as spatial inversions of digital optical signals, which are attributed to the superposition of all orthogonal AGPP modes along the propagation direction. The designed GIWAL, which resembles the Mikaelian lens developed from well-known Maxwell’s fish-eye lens by utilizing conformal transformation optics, 43 , 44 can converge periodically light waves at the central axis of the lens. By adjusting the filling factor of the dielectric grating in the GIWAL, the modal index of the lens is designed and thus the desired graded index profile of Mikaelian lens is obtained, which can be analytically understood and quantitatively predicted with the effective index method of the AGPPs propagating in a periodic two-medium slab waveguide.…”

Broadband achromatic flexural wave Mikaelian lens for high resolution focusing

“…In this paper, since the governing equations of flexuralwave in thin plates could be established by Kirchoff-Love approximation [29], where the vertical displacement is explained by bi-Helmholtz equation, CTM could be applied under this condition. Enlighted by conformally mapped Mikaelian lens in optics [30,31] and acoustics [32], evanescent waves originating from internal reflection is excited by modifying the refractive index profile of conformally mapped Mikaelian lens to enhance impedance mismatch at the lens/plate interface and contribute to broadband (30−80 kHz) highly efficient (above 75%) achromatic high-resolution flexural wave focusing with full width at half maximum (FWHM) around 0.2λ in thin plate. To implement proposed flexural wave Mikaelian lens, the local refractive index is fulfilled by adjusting the thickness of the thin plate.…”