Design of mid-wavelength infrared multispectral filter arrays based on silicon metasurface structures

Multispectral imaging in the mid-wavelength infrared (MWIR) band is essential for applications such as environmental monitoring, agriculture, and resource exploration. However, traditional systems typically rely on bulky dispersive optics that hinder integration and miniaturization. Here, we demonstrate a fully integrated approach for achieving narrowband, multispectral MWIR detection using a single-layer dielectric metasurface directly combined with a broadband InSb photodetector. The metasurface consists of periodic amorphous-silicon nanocylinders that function as low-loss, high-Mieresonant elements for precise engineering of spectral filtering. By rigorously tuning the geometrical parameters of the nanocylinders including height, diameter, and period, we obtain narrowband transmission peaks with high efficiency at target wavelengths, originating from the controlled excitation of electric dipole and magnetic quadrupole resonances. The designed metasurface arrays exhibit peak transmissions above 90% and the full width at half maximum (FWHM) of each peak is below 200 nm, enabling wavelength-selective detection without using complex optical paths. Furthermore, we integrate such a metasurface array onto an InSb detector with an SU-8 transition layer whose optimized thickness enhances detector absorption while suppressing the parasitic near-field coupling. Simulation results show that, while the planar InSb detector lacks spectral selectivity, the integration of our metasurface structure arrays on the detector can lead to high absorption at selective wavelengths with a very small FWHM. These results provide insights into developing compact, lightweight, and highly integrable platforms for high-resolution MWIR multispectral imaging, paving the way for the development of next-generation on-chip photodetection systems and multifunctional infrared photonic devices.