Optimized Double-Layered Grating Structures for Chem/Biosensing in Midinfrared Range

Abstract

Doubled-layered grating structures (DGSs) fabricated of gold (Au) and silver (Ag), respectively, are proposed for chem/biosensing in the mid-infrared range. The geometry parameters of the DGS sensors are optimized using a rigorous coupled wave analysis (RCWA) method such that the minimum reflectance is obtained at an infrared wavelength of 4.8 µ µ µ µm or 6.7 µ µ µ µm. The magnetic field patterns and Poynting vector distributions within the optimized grating structures are examined using a finite difference time-domain (FDTD) method. The simulation results show that for a resonant wavelength of 4.8 µ µ µ µm, the Au and Ag sensors both have a sensitivity of 2000 nm/RIU (refractive index unit) and 3000 nm/RIU theoretical sensing resolution of 5x10 -6 RIU and of 1x10 -7 RIU, respectively. Similarly, for a resonant wavelength of 6.7 µ µ µ µm, the two sensors have a sensitivity of around 200 nm/RIU and theoretical resolution of 5x10 -5 RIU. In other words, the sensitivity of the DGS sensors optimized for an infrared wavelength of 4.8 µ µ µ µm is one order higher than that of the sensors optimized for a wavelength of 6.7 µ µ µ µm. In general, the results presented in this study show that the proposed DGS sensors provide a simple and versatile solution for performing chem/biosensing at midinfrared wavelengths.Index Terms-Doubled-layer gratings structure, mid-infrared wavelength, surface plasmon polaritons, cavity resonance, 1530-437X (c)

A subwavelength metal-grating assisted sensor of Kretschmann style for investigating the sample with high refractive index

“…where the plasmon frequency of ω p = 1.447 × 10 16 rad/s and the collision frequency of V c = 8.33689 × 10 13 rad/s are obtained from the best fit of experimental values for the wavelength ranging from 350 nm to 800 nm. [15,16] substrate (ε g )…”