Enhanced Refractive Index Sensing in an Ag-Dielectric-Ag Plasmonic Waveguide with an Embedded WS2 Layer

We design and analyze a plasmonic metal–dielectric–metal waveguide sensor with a WS2 nanolayer embedded within the dielectric core. We analyze the effect of the WS2 position and thickness on the transmission spectra, resonance characteristics, electromagnetic-field distribution, and refractive-index sensitivity using the finite element method. We compare three configurations: an MDM waveguide without WS2, a structure with WS2 at the metal–dielectric interface, and a structure with WS2 embedded within the dielectric core. The results show that the position of the WS2 layer changes the resonance characteristics and electromagnetic field distribution of the waveguide. We further optimize the WS2 thickness and identify 5 nm as the optimized thickness. Within the refractive-index range of 1.33–1.40, the optimized structure provides sensitivities of 504 nm/RIU and 571 nm/RIU for the dip and peak resonances, respectively. The sensing performance is further evaluated using the full width at half maximum, figure of merit and quality factor. We also examine a hybrid configuration by adding a graphene layer at the metal–dielectric interface. However, the graphene layer does not provide any additional improvement in sensing performance compared with the optimized WS2 configuration. These results show that the position and thickness of the WS2 layer are important parameters for controlling the resonance response and refractive-index sensing performance of compact plasmonic waveguides.