Chirality‐Reversed Bidirectional High‐Efficiency Dichroic Metalens based on Hybrid Helical Surfaces

Abstract

A conventional chiral metalens based on helical structures have the disadvantages of fixed chirality and low conversion efficiency of cross-circular polarization. In this study, a chirality-reversed bidirectional high-efficiency dichroic metalens based on hybrid helical surfaces (HHSs) is proposed and experimentally demonstrated, which is composed of a pair of half-pitch helical surfaces with left-and right-handedness. It is found that the cross-polarization conversion efficiency of the hybrid structure reaches 78.5%, which is ≈20 times higher than that (≈4%) of a conventional normal helical structure. The chirality of the hybrid structure can be flexibly switched between left-and right-handedness by simply flipping the metalens by 180°, rendering a chirality-reversed bidirectional operation. A comprehensive analysis of the physical mechanism and experimental verification are conducted. Two-photon laser direct writing and electron beam evaporation are employed to fabricate the dichroic metalens with a scale of a 101 × 101 HHS array, and dichroism focusing and imaging are successfully realized by lock-in thermography in the IR wavelength range from 3 to 5 𝝁m. The demonstrated high-efficiency bidirectional dichroic metalens promises important applications in polarimetric imaging and biomedical chirality detection.

Recent Advances and Prospects of Optical Metasurfaces

“…To overcome these obstacles, metasurface designs are experiencing diverse upgrades, such as from ordinary nanostructures (nanofin, nanorods, etc.) to units with irregular shapes ,,, (3D nanostructures, multipole resonance units, etc. ), from a single layer to multiple layers, ,,,, and from a single material to a composite material. ,, In particular, inverse design considers the global response and supports aperiodic surface morphology, which is expected to empower further metasurface research and applications.…”

“…To overcome these obstacles, metasurface designs are experiencing diverse upgrades, such as from ordinary nanostructures (nanofin, nanorods, etc.) to units with irregular shapes 54,58,59,183 (3D nanostructures, multipole resonance units, etc. ), from a single layer to multiple layers, 32,43,58,59,146 and from a single material to a composite material.…”

“…), from a single layer to multiple layers, 32,43,58,59,146 and from a single material to a composite material. 105,183,184 In particular, inverse design considers the global response and supports aperiodic surface morphology, which is expected to empower further metasurface research and applications.…”

Two-photon polymerization lithography for imaging optics

“…Conventional chiral metalenses with fixed helical structures suffer from constrained chirality and low cross-circular polarization conversion efficiency. Wang and Wang introduce a hybrid helical surface that fosters bidirectional chiral metalensing, achieved by 3D printing the halfpitch helical surface and subsequently coating it with a gold film [210]. Notably, the cross-polarization conversion efficiency achieves an impressive 78.5%, a stark enhancement compared to the conventional normal helical structures, heralding promising applications for high-efficiency chip-scale dichroism and chiral devices.…”

Metalens in Improving Imaging Quality: Advancements, Challenges, and Prospects for Future Display

“…[29] Fan et al created a neural nanophotonic light-field camera with an exceptionally deep depth of field (DOF) in the same year, drawing inspiration from trilobites and combining it with a convolutional neural network reconstruction method. [30] As research into metalens continues to advance rapidly, it is increasingly applied across the visible and near-infrared spectrums, [31][32][33][34] and the ultraviolet band has also been steadily investigated. [35][36][37] For instance, Ossiander et al in 2023 effectively focused ultra-short EUV light bursts caused by high harmonics to the waist of 0.7 micron using extreme ultraviolet metalens with a focal length of 10 mm.…”