Research On Displacement Sensing Characteristics Of Optical Microcavity Based On Surface Nanoscale Axial Photonics Structure

In recent years,due to the extremely small mode volume and extremely high quality factor,the whispering gallery mode(WGM)microcavity has received extensive attention in the field of sensing,especially in displacement sensing applications.Although the displacement sensing technology based on the whispering wall microcavity has been continuously progressing and developing,in practical applications not only need to improve the performance of the microcavity,but also strongly depend on the sensing scheme used.In this paper,a new type of displacement sensing scheme based on the surface nanoscale Axial Photonics(SNAP)structure microcavity is proposed.The new type of sensing scheme can not only avoid the interference of external unfavorable factors,but also obtain simple rules.By solving the resonance spectrum of multiple axial modes,large-range and high-resolution displacement sensing can be realized.Therefore,this article discusses and researches the theory and experiment of the new displacement sensing scheme.The specifics are as follows aspect:(1)Based on the mode theory and coupling theory of SNAP microcavity,the SNAPfiber coupling system is modeled and simulated by MATLAB numerical calculation.By controlling the coupling parameters and the SNAP mode parameters,the changing laws of resonance spectrum characteristics are studied.By analyzing the actual meaning of each parameter,we have obtained helpful guidance for the experimental process,which has important value in practical applications.(2)By analyzing the surface graphs of resonance spectra with different coupling positions,ideal coupling parameters and mode parameters for displacement sensing are obtained.The influence of the sensitivity threshold and the number of excited modes on the displacement sensing characteristics is studied.The results show that the sensitivity under certain conditions can be achieved by adjusting the transmittance threshold.The number of excited modes during the sensing process determines the sensing range.Quantitative analysis of sensitivity and range of single-order and multi-order resonance spectra is carried out,and finally the feasibility of multi-order axial mode joint sensing is demonstrated.When the first21-order axial mode is excited,when the sensitivity threshold is set to 0.05 and the resolvable transmittance of 1/1000 changes,the sensing range can reach 183.17?m and the resolution is 20 nm.(3)Based on simulation principles and numerical calculation results,we built a fusion tapering system and fabricated fiber cones with a waist size from 3?m to 1?m.At the same time,we fabricated a usable SNAP microcavity by arc discharge method.Finally,through processing and purchase,a set of precision tuning platform was built to realize the coupling of fiber cone and SNAP microcavity.By moving the microcavity axially,stable and controllable coupling is achieved,and 130 sets of axial modes in the cavity are excited equidistantly within a 65?m sensing range.With the help of the fitting alignment algorithm,the experimental resonance spectrum surface map is obtained,and the positioning and recognition of the resonance mode is realized.The experimental phenomenon is very consistent with the theoretical calculation result.