Sensing mechanism of an Au-TiO2-Ag nanograting based on Fano resonance effects

In recent years, with the development of nano-photonics, Fano resonance has gained increasing attention. Due to its high sensitivity, real-time detection, and label-free properties, the Fano resonance sensor has been widely applied in the fields of biochemistry and environmental detection. To improve the sensing characteristics of Fano resonance, an Au-TiO2-Ag grating structure is proposed in this paper, and the sensing performance is enhanced by a bi-metallic grating and deposited TiO2. The characteristics of both sensing and field distribution of the model are accordingly analyzed using the finite-difference time-domain method. By varying the structural parameters such as grating period, grating height, silver film thickness, and TiO2 layer thickness, the tuning of sensing characteristics can be realized, and afterwards, the sensing performance is improved; consequently, the Fano resonance reflection spectrum with high sensitivity and a high figure of merit (FOM) value is obtained. When the grating period P = 200 nm, grating height T1 = 90 nm, silver film thickness T2 = 20 nm, TiO2 layer thickness T3 = 20 nm, and SiO2 layer thickness T4 = 600 nm, such a structure indicates favorable sensing performance, and sensor detection accuracy can reach 10-3; maximum sensitivity is 1400 nm/RIU, and maximum FOM can reach 4212RIU-1. The results demonstrate that the designed Fano resonance sensing model has good potential for application.