Gas sensing performance of high-Q photonic crystal nanocavities based on a silicon-on-insulator platform

Abstract

We have proposed and theoretically analyzed the gas sensing performance of the photonic crystal (PhC) nanocavities based on a silicon-on-insulator platform. To assess the gas sensing performance of the proposed PhC nanocavities, the effect of the etch-depth of the circular air holes in the substrate on the quality factor, mode volume, and resonant wavelength have been analyzed. Numerical analysis carried out using the three-dimensional finite-difference time-domain method and filter diagonalization approach shows that the etch-depth significantly perturbs the electric field profile of the original cavity mode. By tuning this parameter, the antinodes of the electric fields are relocated to the air regions of the etch-depth, which leads to an increase in the quality factor and reduction in the mode volume. In this case, the quality factor is found to increase with increasing etch-depth, but still remains as high as 5170 with a small modal volume of $$0.95~(\lambda /n)^{3}$$ . In addition, using the perturbation method, we have demonstrated that the proposed PhC nanocavities possess the capability of detecting the change in the refractive index of the surrounding gas target with a high sensitivity of 322 nm/refractive index unit (RIU) and a detection limit of $$10^{-3}\,RIU$$ . We believe that our proposed PhC nanocavities, which exhibit excellent sensing performances, ultra-small mode volume, and a compact footprint, may offer the potential to develop on-chip sensing devices for applications in gas detection.