Non-polarized and ultra-narrow band filter in MIR based on multilayer metasurface

We propose an ultra narrow-band filter in the mid infrared region (MIR) using artificial metamaterials (AMM), which is suitable for the design of on-chip photonic spectrometers. 2-D rectangular holes with a cross-like layerout are adopted to enhance the filter's efficiency and precision. Considering the penetration depth of electromagnetic (EM) waves in the metal film, we opt for multi-layer films composed of metal layers and dielectric layers, instead of a single metal layer, to improve the structure's performance in the MIR. This multilayer configuration significantly enhances the efficiency and precision of the AMM structures in the MIR. The transmission peak, with a full width at half maximum (FWHM) of 30 nm, can be achieved and tuned in the wavelength range from 3.0 μm to 10.0 μm by changing the periods of the unit cell (enlarging the unit cell from 3.0 to 10.0 μm). The proposed AMM structures, with tunable narrow band transmittance in MIR, exhibit promising potential in the fabrication of narrow band photonic detectors and on-chip spectrometers.