SOI Suspended membrane waveguide at 3.39 μm for gas sensing application

In this letter, we present a numerical study on designing a silicon-on-insulator (SOI) suspended membrane waveguide (SMW). The waveguide geometry is optimized at 3.39 mu m TE-polarized light which is the absorption line of methane gas by utilizing a 3D finite element method (FEM). The transmission loss (TL) and evanescent field ratio (EFR) of the waveguide are calculated for different geometric parameters such as the width of core, height of core and period of the cladding. We found out that TL is directly related to EFR. Therefore, waveguide geometry can be designed which can offer high EFR at the cost of high TL or low EFR with low TL, as desired. Based on the geometric parameters used in this paper, we have obtained a TL and EFR which lies in the range of 1.54 divided by 3.37dB and 0.26 divided by 0.505, respectively.