Study On Fano Resonance Sensing Properties Based On Photonic Crystal Nano-beam Cavity

In recent years,the photonic crystal micro-cavity structure has advantages such as high Q value,small mode volume,easy integration,and simple manufacturing process,which has made it widely used in the design of nano-sensing structures,and researchers try to further improve the sensing performance of the structure by exciting Fano in the photonic crystal micro-cavity.Based on the study of the characteristics of the photon micro-cavity and the formation mechanism of the Fano resonance,the Fano resonance was combined with the one dimensional photonic crystal micro-cavity to design the sensing structure,and the transmission characteristics of the structure were qualitatively analyzed in conjunction with the coupling mode theory.The influence of the structural parameters on the transmission spectrum and sensing charact eristics was quantitatively analyzed using the finite difference time domain method.Three types of one-dimensional photonic crystal micro-cavity structures are mainly studied in this paper,which are the uniform aperture type,the chirped aperture type and the cascade type.The main research contents of the paper include:Firstly,based on the photonic band gap and photon local ization characteristics of photonic crystal,the transmission characteristics of one-dimensional photonic crystal nano-beam and nano-beam cavity structure are studied and analyzed.The finite difference time domain method simulation software is used to analyze the influence of the number of air holes,the radius and the arrangement period on the transmission spectrum characteristics,and to grasp the law of the influence of the structural parameters on the transmission spectrum.Furthermore,when designing the sensing structure,appropriate structural parameters can be selected according to the position of the resonance peak and the requirements of the band.Secondly,based on the principle of Fano resonance and the characteristics of photonic crystals,a photonic crystal nano-beam side coupled uniform aperture nano-beam cavity structure was proposed,On this basis,in order to enhance the local ability of light in the resonant cavity,the concept of aperture chirp was introduced in the design of the photonic crystal nano-beam cavity structure.The structural parameters were optimized by the control variable method to obtain better sensing performance.After comparative analysis,the(Figure of Merit,FOM)FOM value of the structure was improved by an order of magnitude compared to the uniform aperture nano-beam cavity.Finally,a dual Fano resonance structure with a photonic crystal nano-beam side coupled to a cascaded nano-beam cavity is proposed.Through the study of single Fano resonance,it can be found that a resonant cavity can generate a resonant valley as a discrete state.Therefore,an attempt was made to introduce another resonant cavity to generate two resonant valleys to form a dual Fano resonance.Studies have shown that the dual Fano resonance structure can not only realize refractive index sensing of the object to be measured,but also can be used as differential sensing to eliminate errors that may occur in the environment to be measured and improve the accuracy of sensing.