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

This study introduces a novel hybrid plasmonic waveguide (HPW) architecture composed of a SiO₂ substrate, a silicon column featuring an isosceles triangular tip, and a silver (Ag) cladding layer that excites surface plasmons in the intermediate SiO₂ region. By modifying the triangular geometry to a scalene form, the electric field distribution shifts from the waveguide center toward its edges, enabling efficient optical coupling when multiple waveguides are placed at an optimized separation. Numerical simulations demonstrate that the coupling coefficient can be precisely tuned as a function of waveguide spacing, achieving a low-loss 3 dB directional coupler. Furthermore, the same structure is utilized to design a refractive index (RI) sensor. By terminating both ends of one HPW with gold layers, a linear resonator is formed. The introduction of an analyte between the coupled waveguides results in detectable spectral shifts. The proposed sensor operates effectively across an RI range of 1.0–2.0, achieving a sensitivity of 15 THz/RIU (≈ 112 nm/RIU at 200 THz) and a quality factor (Q) of 500. The combination of structural simplicity, broad applicability, and strong performance underscores the potential of the inverse V-type HPW as a robust platform for integrated photonic circuits and high-performance sensing applications.