Highly sensitive refractive index sensing with a perfect MIM absorber in visible to near-infrared range

An innovative metasurface refractive index sensor that operates in the visible to near-infrared (NIR) range is introduced in this work. The sensor has a unique half-ring, half-square split design which allows it to reach dual absorption peaks, resulting in near-perfect absorption values of 99.97% in the visible range and 99.99% in the NIR region. Reaching 530.05 nmRIU-1for the visible spectrum's first peak and 620.24 nmRIU-1for the NIR's second peak, the resonant structure has remarkable refractive index sensitivity. Additionally, the metasurface's highest figure of merit of 13.88 RIU^-1highlights how effective it is in detecting refractive index. The sensor has a robust linear response to changes in the refractive index and functions efficiently throughout a range of 1 to 1.5. Through the utilization of both surface plasmon resonance and Fabry-Pérot cavity resonances, the device's distinct design improves light-matter interaction, which in turn increases sensitivity and absorption. Finite element method simulations in the frequency domain revealed the optimal geometric parameters for maximum performance. With its high absorption capacity and polarization insensitivity, this unique design provides a flexible platform for use in chemical detection, environmental monitoring, and biosensing. The structure's scalability and tunability further increase its potential for useful sensing solutions in a variety of industries.