The Study Of Sensor Based On Cascaded Micro-ring Resonators

In recent years,optical sensors have been widely reported to be used in many fields,such as gas monitoring,chemical analysis,and biological sensing.Silicon on Insulator(SOI)waveguide with high refractive index difference between core and cladding,is compatible with Complementary Metal Oxide Semiconductor(CMOS)technology,so large-scale photonic integration can be achieved.A variety of silicon-based integrated optical sensors have been reported.Since micro-ring resonator allows optical signal to be circulated continuously in its cavity,which is equivalent to increasing the length of the sensing arm,it can achieve higher sensing performance with a smaller size.However,most researches currently focus on improving either the sensing sensitivity or the sensing range.The purpose of this thesis is to design some new structures based on cascaded microring resonators,so as to improve the sensing sensitivity and the sensing range simulataneously.Firstly,the coupled-mode theory and sensing theory was given.Then by introducing the vernier effect,a sensing structure based on the cascaded U-shaped waveguide nested micro-ring was proposed.The structure is composed of micro-ring resonators and U-shaped waveguide,which improve the sensing range and sensing sensitivity.The parameters such as the radius of the micro-ring,the coupling distance,and the length of the U-shaped waveguide were designed and optimized by transmission matrix method,.The simulation results show a sensing sensitivity of3794.025 nm/RIU and a sensing range of 0.0256 RIU,respectively.it has a detection limit of 2.636×10^-6 RIU with a spectral resolution of 0.01 nm.Compared with the sensor based on a single micro-ring,simulataneous improvement of sensing sensitivity and sensing range is achieved.In addition,on the basis of a series-coupled micro-ring resonators,a sensing structure based on slot waveguide is designed.Parameters such the slot waveguide gap size,coupling gap size,and the radius of the inner and outer waveguide was optimized.The simulation results show the sensing sensitivity of the structure is 438.417nm/RIU,and the detection limit is 2.281×10^-5 RIU with a spectral resolution of 0.01 nm.Compared with the traditional micro-ring resonator based on rectangular waveguide,the sensitivity is improved by nearly 6 times.At the same time,it also has a relative large sensing range of 0.108 RIU.