Application of silicon nitride feedback waveguide optical sensing based on Fano resonance

In this paper, the basic principle of Fano resonance and its application in optical sensors are discussed. On the basis of the theory, a feedback waveguide structure based on silicon nitride (Si3N4) material is proposed. The Fano resonance line can be controlled precisely by changing the related parameters, such as the distance between the micro-ring and the feedback waveguide, the period and the radius of the nanopore. The simulation results demonstrate that the designed device generates sharp Fano resonance peaks in a specific wavelength range, in accordance with the theoretical analysis. The sensitivity of 130 nm/RIU and free spectral range (FSR) up to 54.55 nm, indicated that it is suitable for high-precision chemical and biological analysis. Compared with traditional optical sensors, the device structure based on silicon nitride material exhibits large detection bandwidth, high sensitivity and ultra-low insertion loss. In addition, the footprint of the designed device is 25 × 15 um, which is smaller than conventional microring resonant cavities. With the advantages of the ultra-compact, large detection bandwidth, high sensitivity and low insertion loss, the proposed feedback waveguide can be widely used in biochemical detection, environmental monitoring, food safety and medical diagnosis.