Ultrahigh sensitive gas sensors based on slotted photonic wire-based structures including optical microcavities

In this paper, we investigated two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) simulations to provide ultrasensitive gas sensors based on silicon-on-insulator (SOI) slotted photonic wire structures in the mid-IR spectral region, tuned for the wavelength 3.392 μ m . The proposed optical microstructures have the ability to detect methane gas in the environment in addition to sensing the gas flux from the hole/slot regions with a very high sensitivity ( S = 2.97 ) through a very high confinement of the electric field in the photonic wire slot region that leads to an increase in the interaction of light with gas. To further boost the sensitivity of the SOI slotted photonic wire structure to the methane gas, we designed an optical microcavity in the photonic crystal (PhC) slotted structure. This microcavity can sense the smallest methane gas level ( 0.36062 μ m 2 ) with high sensitivity ( S = 27.45 ), by means of strengthening the high-quality factor cavity mode and reduction of effective modal volumes. In addition, the ultra-wide bandgap ( 1.9 μ m ) obtained from Bragg mirrors of the simulated microcavity structures can facilitate us to extend the sensing in a wide range of wavelengths.