Theoretical and experimental study of a surface plasmon sensor based on Ag-MgF₂ grating coupler

To achieve a high-sensitivity surface plasmon resonance sensor, a sensor based on Ag-MgF₂ grating was designed and fabricated. A suitable-thickness MgF₂ was suggested to prevent the oxidation of silver while avoiding reducing its plasmonic properties. The combination of an interference lithography approach, the material used for the fabrication of grating, and angular interrogation method led to a less costly sensor. The sensitivity and figure of merit of the proposed sensor approached 85.61 deg/RIU and 51 RIU⁻¹, respectively, which is higher than the experimental values reported so far for grating-based sensors. It was shown that by optimization of the silver-based structure, it has great potential for use in sensor applications. It was observed that based on the made grating pattern, the numerical results were closer to experimental results by considering the grating pattern in a sine form. The effect of temperature on sensor performance was experimentally investigated. It was demonstrated that the change in the resonance angle with the temperature in this structure was equal to 0.02 deg/°C and it was also experimentally shown that temperature changes in the analyte refractive index had the most effect on the variations of the SPR response with temperature.