Performance of photonic crystal based gas sensors under the influence of losses

Abstract

Photonic crystals have attracted a great amount of research work in the last 20 years. Initially, their application possibilities concentrated on communications. In recent years, a lot of research has shown the capability of using these crystals in the form of photonic crystal micro cavities (PCM) in gas sensing applications for e.g. environmental monitoring. Since these crystals exhibit so called photonic bands, they allow only certain frequencies to propagate through the structure while blocking other frequencies. These bands depend on a variety of parameters including the refractive indices forming the crystal structure; most importantly, they show a strong response towards refractive index changes. Thus, it is possible to create gas sensors with high selectivity that even react to the small refractive index changes of different gaseous analytes. These structures are often proposed to be used as chemical sensors, since they allow for very high Q values and thus very high selectivity. The performance of such sensors can be easily simulated with help of numerical approaches such as Finite Elements Method (FEM). Previous research that aimed at studying PCM sensors typically neglected losses due to signal attenuation in such simulations. In this paper we subsequently show how the Q values and the related gas sensing performance change with the imaginary refractive index of the crystal structure.