Study of the Sensitivity of D‐Shaped Optical Fiber Sensors Based on Surface Plasmon Resonance with a Silver Pyramidal Nanostructure Coated with a Thin Layer of TiO 2

In this study, a D‐shaped optical fiber sensor based on surface plasmon resonance and incorporating a long pyramidal silver (Ag) bar coated with aT i O 2 $T i O_{2}$ layer is numerically analyzed using the finite element method. This structure enables the generation of plasmonic waves through the interaction of free electrons in the metal with evanescent waves. The main objective is to identify the most efficient configuration for detecting refractive index (RI) variations in biological media by adjusting the geometrical and physical parameters of the sensor. The sensor's sensitivity to RI variations is determined from optical spectra, particularly through dielectric loss function curve and transmittance spectra. The figure of merit and the sensor's resolution are calculated and analyzed to evaluate its detection performance. The results reveal efficient detection of RI variations in the infrared range, with performance significantly enhanced by tuning theT i O 2 $T i O_{2}$ layer thickness and the height of the pyramidal Ag bar. The sensor achieves a maximum sensitivity of4215   nm / RIU $4215 n m / R I U$ when the RI( n a ) $ n_{a} $ increases from1.31 $1.31$ to1.45 $1.45$ , with aT i O 2 $T i O_{2}$ layer thickness of30   nm $30 n m$ and Ag layer height of70   nm $70 n m$ . The analysis highlights the critical role of theT i O 2 $T i O_{2}$ thickness in improving the sensor's sensitivity.