Chiro-optical effects offer a wide range of potential applications in nanophotonics, such as advanced imaging and molecular sensing and separation. Flat single-layer metasurfaces composed of subwavelength meta-atoms have gained significant attention due to their exceptional characteristics in light–matter interactions. Although metasurface-based devices have manipulated electromagnetic waves, the compact on-chip realization of giant chiro-optical effects remains a challenge at optical frequencies. In this work, we experimentally and numerically demonstrate an all-dielectric metasurface to realize large chiro-optical effects in the visible regime. Notably, the proposed strategy of utilizing achiral nanofins instead of conventional chiral structures provides an extra degree of design freedom. The mutual coupling between carefully engineered nanofins produces constructive and destructive interference, leading to the asymmetric transmission of 70% and average circular dichroism exceeding 60%. We investigate the underlying mechanism behind the chiro-optical effects using the theory of multipolar decomposition. The proposed design mechanism maximizes the chiro-optical response through a single-layer metasurface with potential applications in high-efficiency integrated ultrathin polarization rotators and shapers, chiral polarizers for optical displays, chiral beam splitters, and chiral sensors.
Futuristic holographic displays will essentially require broadband chiro‐optical effects for medical imaging, virtual reality, smart security, and optical encryption. However, conventional metasurfaces cannot provide such on‐chip realization of broadband chiro‐optical effects. Moreover, the simultaneous conversion of amplitude, polarization, and phase (APP) at optical wavelengths to introduce giant chirality has not been realized yet. In this paper, a planar all‐dielectric metasurface is proposed incorporating extra degrees of freedom to comprehend the conversion of APP with broadband chiro‐optical effects in terms of giant asymmetric transmission with maximum efficiency of ≈77% at the wavelength of 567 nm. The underlying mechanism behind induced chiro‐optical effects is also investigated using higher‐order multipolar dielectric resonances. Moreover, experimental validation is performed using the reproduced polarization‐encrypted meta‐holograms at broadband visible wavelengths. This work expands the scope of meta‐nanophotonics with potential applications in bioimaging and polarization‐encrypted displays for healthcare and smart security applications.
comes from a Greek word that means "the hand." Any pairs of geometric figures or groups of points hold the chirality if they are mirror images of each other but cannot be superimposed. [1] These chiral molecules are also named "enantiomers," which can have the same energy levels with different handedness. In zoology [2,3] and botany, [4] chirality plays a substantial role in coloration. Moreover, it is crucial for enantiomer's separation and detection in pesticides, drugs, and amino acids in living organisms. For example, in pesticides, several weed killers contain dichlorprop and mecoprop molecules, where one handedness is herbicide and the other is inactive. [5] Likewise, in the pharmaceutical industry, one enantiomer of the drug, namely thalidomide, is used as relief medicine in pregnant women for morning sickness, but the other enantiomer can cause serious birth deficiencies in children. There are several other examples like levodopa (used to treat Parkinson's disease, but its other enantiomer can lead to severe chronic bacterial infections), ketamine (commonly used anesthetic whose mirror image creates hallucinations), naproxen (used as an anti-inflammatory drug but the mirror image causes liver poisoning), etc. [6][7][8][9] Additionally, all the amino acids, the building blocks of the proteins, are chiral.Left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light have distinct spectral responses, which are regarded as chiroptical effects. [10,11] Examples include optical activity and circular dichroism (CD) or asymmetric transmission (AT). [1,12] Optical activity can rotate the plane of linearly polarized (LP) light (a combination of LCP and RCP).
Next‐generation holographic displays have promising applications in medical science, augmented/virtual reality, smart security, data encryption, etc. Although metasurfaces emerged as the suitable choice to provide compact holographic displays, multifunctionality in metasurfaces at broadband optical wavelengths is inevitable for the abovementioned applications. Here, a metasurface is demonstrated based on chiral structures to introduce multifunctionality in terms of multiple wavefront information depending upon the polarization of incident light. The proposed metasurface integrated with a liquid crystal (LC) provides fast switching and dynamic optical response at broadband visible wavelengths in transmission mode. To avoid the phase distortion in multiple wavefront information embedded into a single planar metasurface, chiral z‐shaped meta‐atoms are used to provide high diffraction efficiency and phase chirality response for circularly polarized (CP) light illuminations. The phase mask of holographic information is encoded into the metasurface using a combination of dynamic and geometric phase modulation techniques. The experimental validation of the designed metasurface is performed to reproduce the spin‐dependent‐specific information at broadband visible wavelengths for changing the polarization of incident light. This research may pave the way toward designing highly efficient multifunctional metadevices to produce next‐generation holographic displays for promising applications in healthcare, media, smart security, and data encryption.
Broadband communication with high data rates is a dire need for state-of-the-art wireless technologies. For achieving efficient wireless communication (particularly in an indoor environment), the electromagnetic (EM) waves should maintain their state of polarization despite encountering multiple reflections. Metasurfaces provide a unique platform to design subwavelength-featured meta-reflectarrays which enable the desired retention of the polarization state of an EM wave upon reflection. We present a single-layered broadband meta-reflectarray, simultaneously breaking n-fold (n > 2) rotational and mirror symmetry, which exhibits an unprecedented control over the phase, amplitude, and polarization of a reflected EM wave. This unique control enables the retention of polarization state and recording of spin-encrypted information for the reflected EM waves. Such novel multifunctional meta-reflectarray can be crucial to building an indoor setup for high data rate wireless communications. Meanwhile, the meta-array’s ability to encode phase information provides an extra degree of freedom to structure and control (via incident spin) the reflected EM beam in the desired way. For the proof of concept, we have experimentally demonstrated a spin-encrypted holographic display which reconstructs the recorded holographic image at an image plane for the left circularly polarized (LCP) illumination and exhibits circular dichroism for the right circularly polarized (RCP) incident waves. The proposed meta-array can find applications in 5G indoor wireless communication, chiral sensing, spin-selective imaging, holography, and encryption.
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