Research On Optical And Thermal Nonlinear Behaviors Of Microcavity Brillouin Laser

As a classic whispering gallery mode(WGM)resonator,silica microsphere cavity has been extensively and deeply studied in the fields of low threshold microlaser,high sensitivity sensing and nonlinear optics due to its extremely high quality factor Q,relatively small mode volume V and rich resonant modes.In this thesis,we focus on exploring the related characteristics of silica microsphere cavity in terms of optical and thermal nonlinearity.The main research work is as follows:1.Theoretical study on the nonlinear thermal behavior of silica microsphere cavity based on finite element analysisWe build a thermal model of the silica microsphere cavity by employing a multiphysics analysis software(Comsol).Based on the model,firstly,in the steady state,we analyze the changing trend of the cavity temperature T under the influence of distance g between thermal conductivity and heat source,thermal coefficient y,the sizes D1 of cavity and the size D2 of thermal conductivity.In the transient state,we analyze the relationship between the the cavity temperature T and thermal response time t.Next,we study the effect of its geometric structure on its thermal conductivity and thermal power based on a silica microcavity Brillouin laser.2.Research on the thermal sensing characteristics of silica microsphere cavityWe select fiber optic spheres and glass rod cavities as resonant cavities,and choose fiber spheres,glass rod cavities and metal probes as the thermal conductor.We conduct combined experiments in order to investigate the resonance drift of silica sphere cavities.First of all,spheres fabricated from silica fiber are chosen.The resonance shifts,which achieved by the above three types of thermal conductors,are up to 4.03pm,5.14pm,and 7.61pm.For a sphere cavity with relatively large dimensions,due to that dense mode distribution with small resonance spacing,it is generally difficult to achieve accurate and stable measurements of a single resonant mode drift through an optical spectrum analyzer or by an electrical sweeping method.We propose an indirect method by employing Brillouin lasing in sphere cavity to study its thermal characteristics,that is,resonance shift is indirectly deduced from stimulated Brillouin scattering.We analyze the change of the thermal power of the resonator cavity and the output power of Brillouin laser under the influence of the coupling mode and the distance g between the cavity and the heat source.Finally,we verify the authenticity of the results of the finite element analysis through experiments.3.Experimental exploration on the symmetry breaking effect of silica microsphere cavityWe study the symmetry breaking caused by Kerr nonlinear effect in silica microsphere cavity.Firstly,we deduced the coupling output optical power of the resonator in the two WGM modes of clockwise CW and counterclockwise CCW.Next,an experimental platform for the coupling system is set up for studying the symmetry breaking of lasing light,nonreciprocal optical output of nonlinear phenomena,such as single-mode SBS,cascaded SBS,and four wave mixing generated by SBS,are observed.Finally,we also observe the randomness of the symmetry breaking effect through the non-reciprocal output of stimulated Brillouin scattering.