Mid-infrared Gas and Liquid Sensing Using Highly-Doped Silicon Flat Micromirrors
摘要
In this work, a new class of flat micromirror cavity made of highly-doped Silicon is proposed and investigated using the Finite-Difference Time-Domain (FDTD) numerical analysis technique. By controlling the Silicon’ doping concentration, the resonant wavelength of the supported optical modes can be tuned, and hence, a significant improvement of the quality factor (Q-factor) can be achieved. Furthermore, combining the flat micromirror cavity with a tubular microfluidic channel, in which, homogeneous medium such as gases and liquids, and non-homogeneous fluids, especially colloidal suspensions can be immersed, the sensing mechanism can be successfully established. The working process of the presented sensor consists in monitoring, within the mid-infrared (mid-IR) spectral range, the changes in the effective refractive index of the operating modes induced by perturbation of the fluids’ refractive index (RI). The coupled structure exhibits around the 5.54 μm wavelength, an exceptional sensitivity of 2350 nm per refractive index unit (RIU) with an outstanding figure of merit (FOM) of 4196 for gases. In addition, the architecture demonstrates around the 5.75 μm peak, a sensitivity of 2031 nm/RIU accompanied by an FOM of 5489 for liquids. The detection of limit (LOD) is estimated to be 0.42 × 10− 6 RIU for gases and 0.4.3 × 10− 6 RIU for liquids. Although, the sensor demonstrates the ability to trap a micrometer sized particle suspended in a liquid medium. The proposed device shows excellent sensing performances with multipurpose detection, which suggest its potential use in the future as mid-infrared sensor.