Investigation of a Grating-based SPR Sensor with Suspended Graphene Monolayer and Double-mode Operation

This study presents a graphene-based tunable surface plasmon resonance sensor utilizing an InAs grating. The graphene nanosheet excites the plasmonic mode at the interface with InAs grating. Operating in the mid-IR range, the sensor is designed to detect materials with refractive indices from 1.33 to 1.48. The sensor’s performance is analyzed using the finite difference time domain method, considering the influence of structural parameters. The strong coupling of incident light to the SPR mode on the graphene surface is demonstrated through field distribution analysis. The sensor’s performance is based on the shift of double dips which could provide much accuracy compared with single mode operating sensors. The optimized sensor offers maximum sensitivity and the figure of merit of 3800 nm/RIU and 23 RIU⁻¹ for mode 1 and 2100 nm/RIU and 35 RIU⁻¹ for mode 2, respectively. The presented sensor is applicable as a broadband tunable spectroscopy in the mid-IR range.