Point-defect nanocavities based on silicon planar photonic crystal (PhC) have been optimized and studied for sensing the refractive index of gases in the mid-infrared wavelength region. The point-defect has been introduced at the center of the triangular lattice of the photonic crystal that is made up of circular air holes, making it suitable for probing the properties of the gas found within the cavity. By optimizing the radius and position of the air holes closest to the defect region precisely, on the order of a few nanometers, the ratio of the quality factor to mode volume (Q/V) for the point-defect PhC nanocavities can be increased considerably. Moreover, a perturbation method has been implemented in order to study the resonant wavelength shift of the optimized point-defect nanocavity modes caused by a small change in the refractive index of the gas. The results obtained show that sensitivity of 270 nm/RIU (Refractive Index Unit) and a detection limit of $$10^{-4}$$ 10 - 4 RIU can be achieved for the optimized point-defect PhC nanocavities. These nanocavities have been designed to oscillate at a single mode with a high Q/V thus enabling to sense the refractive index of gases with high sensitivity.

中文翻译：

---

基于高Q/V点缺陷光子晶体纳米腔的中红外气体传感器

基于硅平面光子晶体 (PhC) 的点缺陷纳米腔已被优化和研究，用于检测中红外波长区域中气体的折射率。点缺陷被引入由圆形气孔组成的光子晶体三角形晶格的中心，使其适合探测腔内气体的特性。通过精确优化最接近缺陷区域的气孔的半径和位置，在几个纳米的数量级上，点缺陷 PhC 纳米腔的品质因数与模式体积 (Q/V) 的比率可以显着增加. 而且，为了研究由气体折射率的微小变化引起的优化点缺陷纳米腔模式的谐振波长偏移，已经实施了一种微扰方法。获得的结果表明，对于优化的点缺陷 PhC 纳米腔，可以实现 270 nm/RIU（折射率单位）的灵敏度和 $$10^{-4}$$$10 - 4 RIU 的检测限。这些纳米腔被设计为以高 Q/V 的单模振荡，从而能够以高灵敏度感测气体的折射率。