Design and research of an all-dielectric diatomic metasurface for high-performance circular polarization detection in the mid-wave infrared (<italic>invited</italic>)

ObjectiveAchieving high circular dichroism (CD), low optical loss, and strong design tolerance remains a fundamental challenge for compact mid-wave infrared (MWIR) polarization detection systems. Existing chiral metasurfaces typically rely on quasi-bound states in the continuum (quasi-BICs) to enhance CD; however, their inherently narrow spectral bandwidth and extreme sensitivity to structural asymmetry and fabrication imperfections severely constrain their practical performance. To overcome these limitations, this work proposes a dual-atom Z-type all-dielectric chiral metasurface driven by guided-mode resonance (GMR). By precisely tuning the interatomic spacing to achieve controllable resonance coupling, the proposed structure attains a high-CD response in the MWIR region while maintaining low loss and robust structural stability.MethodsThis paper presents a diatomic Z-shaped all-dielectric chiral metasurface for mid-infrared polarization detection. Guided-mode resonance is introduced to enhance circular dichroism and enable selective coupling of circular polarizations (Fig.1). Finite-element simulations are conducted to analyze transmission spectra and near-field distributions, revealing diatomic coupling effects (Fig.2). The calculated band diagram confirms that the observed high CD originates from GMR modes (Fig.3). The CD and circular polarization extinction ratio are further evaluated (Fig.4). Angle-resolved analyses under varying polar and azimuthal angles demonstrate anisotropic dispersion behavior (Fig.5), while near-field field maps identify the selective excitation of RCP and LCP waves (Fig.6). Parameter sweeps of geometric dimensions clarify their effects on resonance tuning and CD intensity (Fig.7). The metasurface is fabricated using electron-beam lithography (Figs.8-9), and its optical response is experimentally verified through FTIR-based polarization spectroscopy (Fig.10).Results and DiscussionsThe proposed dual-atom Z-type all-dielectric chiral metasurface exhibits strong circular polarization selectivity in the mid-infrared. Introducing an inter-supercell spacing of Δd=150 nm produces narrow transmission dips at 3162 nm and 3206 nm with a maximum circular dichroism of 0.93, while near-field analysis confirms that selective coupling of right- and left-handed circular polarizations to guided-mode resonances (GMRs) drives the enhanced CD. Angle-resolved studies reveal pronounced dispersion along the long-period (Px) direction, where increasing polar angle redshifts transmission dips and CD peaks, whereas the short-period (Py) direction remains nearly insensitive. Parametric tuning of arm lengths, widths, and lattice periods flexibly shifts resonance wavelengths within MIR while preserving high spectral quality and robust CD. These results demonstrate that the metasurface combines high CD, anisotropic dispersion, and favorable design tolerance, offering a practical route toward compact mid-infrared polarization detection and on-chip integration.ConclusionsThis study proposes and designs a diatomic Z-shaped all-dielectric chiral metasurface based on guided mode resonance excitation, achieving a circular dichroism response of up to 0.93 in the mid-infrared. Finite element analysis results show that the transmission dips under different chiral incident conditions closely correspond to localized near-field enhancements, confirming that the CD enhancement originates from selective coupling of GMRs. Incident angle analysis further reveals that the structure exhibits significant dispersion along the long-period direction while remaining virtually unaffected in other directions, indicating that the strong CD is primarily driven by GMRs in specific directions. Flexible manipulation of geometric parameters allows for effective tuning of the resonant wavelength and optimization of the CD intensity and quality factor. Compared to existing enhancement methods relying on Q-BICs, the proposed scheme achieves high CD response in the MIR while offering advantages in device stability and manufacturing tolerances, demonstrating its potential for application in MIR polarization detection and on-chip integration.