Ultra-Sensitive Chemical Gas Sensor based on Slot and Cavity Strip Silicon Waveguide

Identification and analysis of chemical compounds and products are of great importance for researchers in Chemistry, especially in the Organic and Analytical Chemistry. Accordingly, chemical sensors due to their sensitivity to change and certain chemical compounds, can identify these compositions, and provide information which needed by researchers to analyze. In this paper, an ultra-sensitive optical sensor (S≈2.5) is introduced for chemical gases such as CH4, CO, CO2, NO, N2O and H2O as well. Due to the high optical power, and consequently, the increased risk of the reaction of combustible chemical gases in the earlier sensors, the ineffectiveness and the high risk of using those sensors have become more and more recognized. Since the maximum optical absorption of CH4 is in the wavelength of λ = 3.39 μm, therefore He-Ne laser can be used in the studies. Another reason to choose such exciting optical sources are their lower power and thereby they can eliminate the risk of explosion of the combustible gases such as CH4[1,2]. The proposed optical sensor structure in this paper is a slotted strip waveguide in the Silicon core that comprises two cavities (with radius R) which is grown on Silica substrate. The optical interaction of the evanescent field with CH4 gas changes optical parameters such as the effective refractive index [1]. These changes are the basis of sensing in such optical sensors [2]. Hence, in this research, we try to increase the confinement of the electric field in the slotted region and therefore increasing the possibility of optical interaction with CH4 in this region (Fig. 1). This combined configuration causes the proposed sensor to perform extraordinary sensitivity to the gaseous fluids passing through the gap region.