Research On Novel Refractive Index Sensing Technology Based On Micro-ring Resonator

With the rapid development of information technology and continuous progress on integrated optics,sensors based on integrated optical devices are attracting many research interests in the field of optical sensing due to their distinctive advantages such as high sensitivity,easy to be integrated,compact and light in weight.As a typical integrated optical device,silicon-based micro-ring resonators have the characteristics of high Q factor,easy to be cascaded,and the capability for mass production.As a result,they have good potentials in both high-speed optical communications and novel optical sensing applications.On the other hand,refractive index sensing technologies are important in the fields of food safety and inspection,chemical substance detection,biomedicine,and environmental protection applications.By accurately detecting the refractive index of the analytes,information such as purity and concentration of the sample can be estimated.In this paper,we proposed a refractive index sensor based on a few-mode silicon nitride micro-ring resonator structure.It employs the difference of the resonant wavelength shifts among different guided modes for refractive index detection when the index of the analytes changed.Our method has advantages such as high in sensitivity,wide detection range and low temperature sensitivity.We carried out the theoretical study and simulation analysis based on both a coupled-mode theory and the finite-difference method.We designed the few-mode micro-ring resonator and verified the feasibility of the method.In the experiment,we successfully fabricated a two-mode micro-ring resonator based refractive index sensor and systematically measured and analyzed its key parameters such as Q factor and FSR.We carried out refractive index sensing experiments by using mixed solution with different refractive index.In experiment,we achieved a refractive index sensitivity of 91.79 nm/RIU and a refractive index resolution of 10^-5 RIU.The experimental results agree well with that of the theoretical ones.Further improvement in sensitivity can be expected by adopting micro-ring resonator supporting higher order modes and optimizing the sensor structure.