Design and simulation of refractive index sensor based on suspended composite hybrid plasmonic waveguide for sensing mass density of polarizable hydrogen gas

Abstract. Hybrid plasmonic waveguides (HPWs) are capable of supporting subwavelength optical modes. In a composite HPW (CHPW), the propagation loss can be minimized by adjusting the geometrical parameters of its component layers to reduce field flux inside its lossy metal layer. A ring resonator-based plasmonic sensor based on a waveguide structure of suspended CHPW (SCHPW) is designed for gas sensing applications. SCHPWs are applied for the introduced sensor’s 200-nm-wide bus waveguide and 1-μm-radius ring resonator. The operational parameters of the sensor, such as sensitivity and figure of merit (FOM), are investigated in the near-infrared region using a three-dimensional finite-difference time-domain method. For two considered resonances of the proposed sensor, sensitivities of 236.2 and 270  nm  /  RIU with FOMs of 67.4 and 37.5  RIU  −  1 are achieved, respectively. Additionally, for the proposed sensor, a straightforward mechanism for sensing the mass density of the polarizable hydrogen gas is introduced using the theoretical index–density relation of Lorentz–Lorenz. The mass density sensitivities of 358.2 and 409.3  nm  /    (  g  /  cm3  )   are achieved for the two considered resonances for the hydrogen gas at the range of 0 to 0.05  g  /  cm3.