Proposing a low-loss inverse V-type hybrid plasmonic waveguide and its utilization as a highly sensitive refractive index sensor

In this study, we propose a hybrid plasmonic waveguide structure consisting of an SiO2 substrate, topped with a Si column featuring an isosceles triangular tip. Another layer of SiO2 is deposited, followed by Ag, which excites surface plasmons in the SiO2 region between the triangular tip and the Ag surface. By altering the triangle's shape to a scalene configuration, the field focus shifts from the waveguide's center toward its edges. This enables the implementation of an integrated optical coupler when waveguides are placed at an optimal distance. The research demonstrates that the coupling coefficient can be effectively tuned based on the waveguide spacing, achieving a low-loss 3dB coupler. Furthermore, leveraging this structure, we design a refractive index sensor. By terminating both ends of one waveguide with gold, a linear resonator is created. Introducing an unknown refractive index between the two waveguides facilitates sensing. The proposed sensor operates for refractive indices ranging from 1 to 2, with a quality factor of 500. The simplicity of the design, coupled with its broad applicability, distinguishes the proposed structure as a promising solution for integrated photonic devices and sensing applications.