Sensitivity Enhancement of Silicon Strip Waveguide Ring Resonator by Incorporating a Thin Metal Film

Abstract

In this work, we proposed a metal-assisted silicon strip waveguide design for highly sensitive refractive index sensing applications. To prove the superiority of our proposed design, we make a fair comparison with the standard silicon strip waveguide of comparable geometry. In metal-assisted waveguide structure, a thin SiO2 layer is sandwiched between gold and silicon strip waveguide. The transmission spectrum and E-field distribution of these structures are simulated using 3D-Finite Element Method (FEM). In the first part of the paper, we demonstrated the enhancement of the evanescent field in the upper cladding region of a straight strip waveguide which makes it an ideal candidate for evanescent field gas absorption sensor. In the second part, we designed a metal-assisted silicon strip waveguide ring resonator of radius $1.5~\mu \text{m}$ and verified its higher sensitivity, Q-factor and figure of merit compared to standard ring resonator. The maximum sensitivity of 300 nm/RIU is obtained which is ~67% higher than the sensitivity of a standard ring resonator design when sandwiched SiO2 layer is equal to 50 nm in our proposed design. We believe that our study will provide new favourable circumstances to design sensors with improved sensitivity.