Preparation And Morphology Dependent Resonances Characteristics Of Whispering Gallery Mode Microsphere

Whispering Gallery Mode is an acoustical resonance phenomenon.In the field of optics,this resonance phenomenon,which depends on geometrical properties such as size,shape,and material properties,is also described as morphology dependent resonances.The spherical resonator is studied earlier and can be applied to the field of flow parameters detection.It can achieve high sensitive sensing including the temperature,pressure and other parameters under complex flow conditions.Due to the small size,the microspheres are easy to install and do not affect the flow field,which can realize multi-parameter sensing and distributed detection.In this paper,we mainly explore the whispering gallery mode of micro cavity and the tapered fiber-microsphere system,including the theoretical analysis,model simulations and experiments.More details are as follows:Firstly,we introduce the research background and significance of the micro cavity of WGM,and discuss the research status of microsphere and coupling system.Then we determine the research objectives of this paper.Secondly,we analyze the distribution of WGM microsphere based on the Maxwell equation.Several important parameters of microsphere are introduced.At last,the coupling characteristics of microspheres and tapered fibers are analyzed in detail.Once again,we simulate the whispering gallery mode of microsphere by the software COMSOL,based on the previous theoretical analysis.Since the three-dimensional simulation is computationally intensive and the coupling is very difficult,we first introduce a method to reduce the 3D model to a 2D model.At the same time,according to the communication theory of the WGM,we can know that the resonant surface and the tapered fiber are in the same plane,which can determine the feasibility of the two-dimensional simulation.Next,we simulate the coupling system and analysis the results in detail.Finally,we carry out laboratory preparation on the basis of theory and simulation.In this thesis,we have two kinds of medium microspheres: One is PDMS microspheres,another is the magnetic microspheres containing carbonyl iron powder based on PDMS,and the size of microspheres are 45-200?m.According to the size relationship between microspheres and tapered fibers,2-5?m tapered optical fibers are prepared and the coupling and testing system are designed.In the region of coupling,the tapered fibers and microspheres are respectively fixed on the two-dimensional platform and three-dimensional precision platform.The best effect of coupling is achieved by constantly adjusting the relative position between microspheres and tapered fiber.Through the experiment,the resonance spectrum of the WGM microspheres was obtained at 1520 nm-1570 nm wavelength.Affected by the accuracy of experimental equipment,the quality factor can reach 104,but the actual value is much higher than the test.By further studying the composite application of pressure,temperature and magnetic field sensing,WGM microspheres are of great study significance for realizing distributed detection of the flow field.