Parameter Analysis Of Tapered Fiber And Coupling Characteristics Of Whispering Gallery Microsphere

Due to the high quality factor,small volume mode,and good mechanical stability,the whispering gallery mode,optical resonator has attracted more and more attention.The way to guarantee the effective coupling of the resonator is an important link to realize the WGM and get the effective output.In order to effectively achieve the coupling between microsphere resonator and the tapered fiber,the parameters of the tapered fiber are analyzed.Three coupling states of the system are analyzed in terms of the transmissivity of the system,such as under coupling,critical coupling and over coupling.Based on the basic characteristics,ray theory and waveguide theory of the tapered fiber,the propagation constant of the tapered zone and cone waist are studied respectively.And the evanescent field of the tapered fiber and the effect of evanescent field on the fiber loss are analyzed.Through the theoretical analysis of the forming process of tapered fiber,the relationship between the mode field distribution,the optical power distribution and the diameter of the fiber core are obtained.The tapered optical fiber with a diameter of about 2.8?m is successfully drawn by using the hydrogen oxygen flame drawing system when the stretched length is 15 mm.In order to carry out the coupling experiment between microsphere and tapered fiber,the distribution of photons at the waist of tapered fiber is studied.The Monte Carlo method is used to analyze the distribution of photons at the waist of the tapered fiber when the photons are incident one by one continuously.The result shows that the smaller the diameter of cone is,the more the number of photons escaped from the tapered fiber is.Then the distribution of electric field component Ez in X-Y surface at the cone waist is simulated and the results show that:(1)when the relative refractive index is 1,the diameter of cone waist changes from 4?m to 2?m,the constraints capacity of light of cladding is still strong but shows a downward trend when the tapered waist diameter becomes smaller.With the diameter of the cone waist becomes smaller,the distribution of electric field near the cladding gets larger,so is the evanescent field.(2)when the diameter of the cone waist is 3?m,the external refractive index will affect the electric field distribution,the smaller the external refractive index is,the smaller the distribution of the electric field near the cladding is,so is the evanescent field.In order to carry out the verification of parameters of tapered fiber,the coupling experiment of Whispering Gallery Mode microspheres has carried out.The microspheres made of polydimethylsiloxane(PDMS)with the of diameter 144?m and the diameter of 163?m are coupled with the tapered fiber with diameter of 2.8?m,then the quality factor of 7384,the free spectral range of 3.7nm are obtained when the line width is 2pm.