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Chiral metasurfaces have emerged as a useful platform for enhancing the circular dichroism (CD) signals of chiral molecules, and understanding the enantioselective interactions between chiral metasurfaces and chiral molecules is essential. Here, we study the enhanced enantioselective interactions between chiral molecules and eye-shaped chiral metasurfaces by investigating the difference in CD response (ΔCD) and the differential dissymmetric factor of optical chirality (Δg_c) through varying structural parameters of the metasurface. It is shown that strong chiral near-field confinement enhances both ΔCDandΔg_caround the molecule resonance. Meanwhile, the coupling condition of the metasurface with incident light affects the ΔCDresponse of the metasurface-molecule coupled system but has a negligible effect onΔg_c. These results will advance the metasurface-based chiral molecule sensing for potential applications in pharmaceutical drug development and biomedical diagnostics. 

ABSTRACT Ince‐Gaussian (IG) modes are a complete and orthogonal set of solutions to the paraxial wave equation in elliptic coordinates representing a continuous transition between Hermite‐Gaussian modes and Laguerre‐Gaussian modes. Chip‐scale platforms to generate IG beams have great significance for various applications, including optical trapping and micromanipulation of particles, optical communication, and quantum optics. On the other hand, materials with high optical anisotropy are crucial for building polarization‐sensitive optical devices. In this context, niobium oxide dihalides are a new class of ferroelectric materials exhibiting strong, tailorable, and highly anisotropic second‐harmonic generation responses. Here, we report the generation of highly anisotropic second‐harmonic IG beams using binary grating holograms patterned on ultrathin niobium oxide dibromide (NbOBr₂) flakes. Both even and odd IG beams with different mode indices are generated by encoding the phase profiles of the beams into the holograms. According to the polarization‐dependent second‐harmonic generation responses, the relative magnitudes of the second‐order nonlinear susceptibility elements of NbOBr₂crystal are extracted. The results presented here provide new directions for generating complex optical beams with potential applications in classical and quantum photonic integrated devices. 

Abstract Optical vortices have the tremendous potential to increase data capacity by leveraging the extra degree of freedom of orbital angular momentum. On the other hand, anisotropic 2D materials are promising building blocks for future integrated polarization‐sensitive photonic and optoelectronic devices. Here, highly anisotropic third‐harmonic optical vortex beam generation is demonstrated with fork holograms patterned on ultrathin 2D germanium arsenide flakes. It is shown that the anisotropic nonlinear vortex beam generation can be achieved independent of the fork grating orientation with respect to the crystallographic orientation. Furthermore, 2D fork hologram is designed to generate multiple optical vortices having different topological charges with strong anisotropic responses. These results pave the way toward the advancement of 2D material‐based anisotropic nonlinear optical devices for future applications in photonic integrated circuits, optical communication, and optical information processing. 

The coherent superposition of two vortex beams with opposite topological charges gives rise to the formation of petal‐like beams with unique intensity profiles and azimuthal phase structures, offering great potential for various applications. Here, the generation of anisotropic second‐harmonic petal‐like beams is demonstrated using ultrathin niobium oxide dibromide (NbOBr₂) holograms. The polarization‐dependent Raman measurements are conducted on the NbOBr₂flake to reveal the anisotropic properties of the crystal. By imprinting the beam profile information of the superposed vortex beams on the designed NbOBr₂holograms, highly anisotropic second‐harmonic petal‐like beams with different combinations of the topological charges of vortex beams are produced. The results demonstrated here provide a pathway toward the development of chip‐scale polarization‐sensitive functional optical devices for applications in optical communication, optical trapping, and quantum optics. 

Abstract Detection and identification of chiral molecules are important for pharmaceutical industry, clinical analysis, and food analysis. Here, chiral molecular sensing based on spatially selective coupling between achiral metasurface and chiral molecules is demonstrated. The designed achiral metasurface exhibits strong optical chirality and electric field with dissymmetric distribution, and chiral molecules are selectively placed over the area with large optical chirality to form the coupled metasurface-molecule system with circular dichroism (CD) response for chiral molecular sensing. The CD spectra of the metasurface coupled with pure D-alanine enantiomer, L-alanine enantiomer and their mixtures are examined. The linear relationship between the peak CD value and the enantiomeric excess is demonstrated for the detection and identification of pure enantiomers and their mixtures. Furthermore, the CD response of the coupled system shows potential for the sensing of molar concentration of chiral molecules. Moreover, the effect of spatial location of molecules on the CD response is analyzed to show potential for position sensing of chiral molecules. These results of chiral molecular sensing with achiral metasurface offer new opportunities for advancing biomolecular sensing applications. 

Achiral metasurfaces with near-field optical chirality have attracted great attention in molecular sensing and chiral emission control. Here, the circular dichroism (CD) response of an achiral metasurface induced by spatially selective coupling with polymethyl methacrylate (PMMA) molecules is demonstrated. A designed achiral metasurface with a V-shaped resonator exhibits large optical chirality with a strongly dissymmetric distribution under circular polarization. By introducing a PMMA molecule layer on top of the metasurface, which covers the area with large optical chirality, CD in absorption of 0.38 and a dissymmetric factor of optical chiralityg_cof 0.16 are obtained. Furthermore, an analysis of the coupled harmonic oscillator model reveals stronger coupling strength between the PMMA layer and the metasurface under RCP incidence, compared to the LCP case. Moreover, it is shown that the far-field CD response of the metasurface is linearly correlated with the dissymmetric near-field optical chirality distribution. The demonstrated results present the potential for advancing applications in chiral molecule vibrational sensing, thermal emission control, and infrared chiral imaging. 

Abstract Optical vortex beams with helical phase fronts have immense potential to enhance data capacity due to the unbounded values of orbital angular momentum. Chip‐scale platforms for producing vortex beams are of paramount importance for a variety of applications. On the other hand, 2D materials with unique optical properties are essential for developing multifunctional ultrathin photonic devices. Here, anisotropic and temperature‐tunable second‐harmonic vortex beam generation is demonstrated with ultrathin ferroelectric niobium oxide dichloride (NbOCl₂) fork holograms. The polarization‐resolved Raman measurements are performed on the NbOCl₂crystal to understand the anisotropic behavior of the Raman modes. It is demonstrated that the anisotropic and temperature‐tunable second‐harmonic vortex beams can be generated regardless of the relative orientation of the fork gratings with respect to the crystallographic orientation of the NbOCl₂flakes. Furthermore, the Curie temperature of the ferroelectric NbOCl₂crystal is determined according to the measured temperature‐dependent second‐harmonic generation intensities. The results presented here create new opportunities for the development of advanced polarization‐sensitive and temperature‐switchable nonlinear photonic devices used for future applications in integrated photonic devices, quantum optical chips, and optical communication.