Narrowband and flexible perfect absorber based on a thin-film nano-resonator incorporating a dielectric overlay

We developed a flexible perfect absorber based on a thin-film nano-resonator, which consists of metal–dielectric–metal integrated with a dielectric overlay. The proposed perfect absorber exhibits a high quality (Q-)factor of ~ 33 with a narrow bandwidth of ~ 20 nm in the visible band. The resonance condition hinging on the adoption of a dielectric overlay was comprehensively explored by referring to the absorption spectra as a function of the wavelength and thicknesses of the overlay and metal. The results verified that utilizing a thicker metal layer improved the Q-factor and surface smoothness, while the presence of the overlay allowed for a relaxed tolerance during practical fabrication, in favor of high fidelity with the design. The origin of the perfect absorption pertaining to zero reflection was elucidated by referring to the optical admittance. We also explored a suite of perfect absorbers with varying thicknesses. An angle insensitive performance, which is integral to such a flexible optical device, was experimentally identified. Consequently, the proposed thin-film absorber featured an enhanced Q-factor in conjunction with a wide angle of acceptance. It is anticipated that our absorber can facilitate seminal applications encompassing advanced sensors and absorption filtering devices geared for smart camouflage and stealth.