Highly Q-factor plasmonic absorbers are attractive for achieving the higher figure of merit (FOM) and sensitivity in the optical sensors. In this work, an elliptical plasmonic absorber as metal–insulator–metal element is studied analytically with a cross-slot for increasing the Q-factor to concentrate the energy in gaps as a refractive index sensor for the mid-infrared spectrum. The elliptical absorber shows dual-band characteristic in the range of the 100 to 500 THz with sensitivity to incident wave mode and maximum Q-factor of 462 and 227 for TE and TM modes. The final model is selected based on parametric studies for the elliptical absorber for both TE and TM mode and it is simulated with the time-domain method. Finally, the proposed absorber is utilized as an optical sensor with maximum FOM is 88.2 RIU⁻¹ (refractive index unit) and sensitivity of 476 nm/RIU where the nanoparticle is coated with the material under test with refractive indices of 1 to 1.5. So, this optical sensor can be used for a wide range of applications such as detecting blood groups or chemical material.

高 Q 因子等离子体吸收器对于在光学传感器中实现更高的品质因数 (FOM) 和灵敏度具有吸引力。在这项工作中，作为金属-绝缘体-金属元件的椭圆形等离子体吸收体进行了分析研究，该吸收体具有交叉槽，用于增加 Q 因子以将能量集中在间隙中，作为中红外光谱的折射率传感器。椭圆吸波器在 100 至 500 THz 范围内显示双波段特性，对入射波模式敏感，TE 和 TM 模式的最大 Q 因子为 462 和 227。最终模型是基于 TE 和 TM 模式椭圆吸收器的参数研究选择的，并使用时域方法进行模拟。最后，所提出的吸收器用作光学传感器，最大 FOM 为 88.2 RIU ^-1（折射率单位）和 476 nm/RIU 的灵敏度，其中纳米颗粒涂有被测材料，折射率为 1 到 1.5。因此，这种光学传感器可用于广泛的应用，例如检测血型或化学物质。