Analysis of Ultra-Broadband Absorber with Multilayer Structure in Visible to Near Infrared Light

We have designed an absorber with ultra-broadband absorption spanning from visible light to near-infrared light. The performance of the designed absorber was validated with numerical analysis using the COMSOL simulation software. The absorber structure consists of two layers of square cubes stacked on top of four layers of continuous flat films. Starting from the top, the structure consists of an aluminum oxide (Al₂O₃) and titanium (Ti) cube, followed by a four-layer continuous planar film consisting of poly N-isopropyl acrylamide (PNIPAAm), titanium (Ti), silicon dioxide (SiO₂), and titanium (Ti). The simulation analysis results indicated the exceptional performance of this absorber in terms of ultra-broadband. Its high absorption rate was attributed to several factors. Firstly, the top alumina layer exhibits anti-reflection properties, which minimize reflection losses. Secondly, the absorber incorporates three different resonances: local surface plasmon resonance, propagating surface plasmon resonance, and Fabry-Perot cavity resonance. These resonances coexisted within the designed absorber, and at least two of them occurred simultaneously. Thirdly, the formation of two Fabry-Perot cavities within PNIPAAm and silica dielectric layers contributed to the overall performance. The combined effects of anti-reflection, multiple resonances, and the presence of Fabry-Perot cavities enabled the absorber to achieve ultra-broadband absorption and a high absorption rate. Overall, the designed absorber demonstrated remarkable characteristics in absorbing a wide range of wavelengths, from visible light to near-infrared light, while maintaining a high absorption efficiency.