Design and performance of diamond-based mid-infrared sensor

Herein, finite-element analysis is used to optimize the performance of mid-infrared (MIR) (7.7-13.7 μm) waveguides by selecting optimal waveguide and substrate materials, waveguide size, and boundary field. The results show that a diamond waveguide has a substantially higher sensitivity than Si- or Ge-based waveguides owing to its higher boundary evanescent field at the same depth. Furthermore, it is found that AlN substrates have better optical stabilities than SiO${}_2$ and Si${}_3$N${}_4$ substrates, because AlN substrates do not have apparent absorption characteristics in the MIR range (7.7-13.7 μm). Geometry of diamond waveguide on AlN substrate is optimized, and a section length of 45 μm is chosen for optimal signal transmission quality. The calculations of the infrared attenuated total reflection (ATR) of the diamond waveguide applied to water, alcohol, and diisopropyl methyl phosphate are highly consistent with the actual infrared absorption spectrum. This proves the feasibility of applying AlN/diamond waveguides in MIR ATR detection, which is of great significance for the preparation of high-sensitivity MIR detectors. (© 2020 Wiley‐VCH GmbH)