Ultra-high sensitive 2D photonic crystal for gas and chemical sensing applications

Abstract

Mid infrared (MID-IR) band of electromagnetic radiation plays the key role for gas and chemical sensing application because it provides molecular fingerprints for most trace gases and molecules. Photonic crystal cavity coupled waveguide (PC-CWG) based sensors is a remarkable platform for sensing applications due to its capability to confine light modes on small volume displaying high sensitivity and high quality factors. In this work, we report a novel design of (PC-CWG) based on square lattice of silicon pillars in air with radius of 0.2𝜇m and lattice constant of 1 𝜇m. A waveguide is introduced by removing three columns of silicon pillars, and a microcavity is created by removing a number of silicon pillars forming curved shapes on both sides of the waveguide. The proposed design demonstrates multiple resonances covering a broad spectral range in MID-IR ranging from 2.4 𝜇m to 4.2 𝜇m that represents the bandgap region. Remarkable resonances are observed at operating wavelengths 2.67 𝜇m, 2.88 𝜇m, 3.03 𝜇m, 3.2 𝜇m and 3.5 𝜇m. Moreover, the reported design shows ultra-high sensitivity reaching 2680 nm/RIU with a significant quality factor of Q=6475 giving rise to a figure-of-merit of 5.7 × 10 6 at the operating wavelength of (𝜆=3.03𝜇m). The suggested photonic crystal design offers simple fabrication and broad applicability for refractive index sensing applications.