Research On Optical Properties Of Brillouin Lasers Based On Microsphere Resonator

The Whispering Gallery Mode(WGM)microsphere cavity is a typical structure of the optical resonant cavity.Compared with the traditional optical microcavity,it not only has a high quality factor(Q)and size-dependent small mode volume(V),but also has rich resonances.The ultra-high quality factor means long photon lifetime in the cavity.A small mode volume means that the low-power pumped has a high optical energy density in cavity,and the rich resonant mode easily meets the optical resonance conditions required for nonlinear optics.Therefore,microspheres are commonly used in ultra-low threshold lasers,nonlinear optics,and high-sensitivity sensors.In this paper,we mainly explore the application of high-Q quartz microspheres in Brillouin micro-lasers and their thermal sensing.We try to use laser diodes to directly pump microspheres to generate Brillouin lasers,and use microsphere Brillouin lasers to realize optical thermal sensing.The main research contents include:1.Theoretical analysis of the effects of resonance drift on Brillouin laser powerCombining the coupled mode theory with the thermodynamic equations in the microcavity,we derive the relationship between the first-order Brillouin laser output power,the pump wavelength tuning,and the ambient temperature variation:(1)Without considering the resonant mode conversion and others nonlinear effects,the Brillouin output power variation and the pump wavelength tuning are approximately linear;(2)When the ambient temperature increases,the Brillouin output power decreases linearly,and the more quickly temperature increases,the faster the output power drops;(3)When the heat is dissipated,the Brillouin output power increases exponentially.2.Realization of a new type of Brillouin micro laser-External cavity lasing pumped stimulated Brillouin laser(1)Constructing a microsphere feedback fiber laser,the microsphere cavity here is used as a mode-reflecting mirror and to compress the resonance line width.We realize a single-frequency laser output with a line width of-200kHz and the signal to noise ratio of～50dB;(2)Using the fiber-ring microcavity system we realize an external cavity self-pumped stimulated Brillouin laser.In the multi-mode state,the 20dB linewidth at～11GHz is～12kHz,and the 10dB linewidth at～22GH is～4kHz;In the single-mode state,～11 GHz microwave signal 10dB linewidth is～6kHz.3.Experimental exploration on the thermal sensing of microsphere Brillouin laserBased on the theoretical analysis of the influence of resonant wavelength drift on the Brillouin output optical power,the effect of tuning the pump wavelength and changing the ambient temperature on the Brillouin optical power is explored experimentally.(1)First,in order to obtain a stable Brillouin laser,we designed a package structure of cavity-taper coupling.Wideband tunable cascaded SBS,high signal-to-noise ratio cascaded SBS,and "optical frequency combing" induced by backward Stokes photon are realized;(2)By tuning pump wavelength,changing the coupling relationship between pump wavelength.Stokes light and resonant modes,we achieve a linear change of the Brillouin laser power and pump wavelength tuning,and results in agreement with theoretical predictions;(3)Observed optical bi-stablilities induced by the resonant transition of pump wave and Brillouin lasing;(4)Controling the increase(decrease)of the ambient temperature by heating(stopping the heating)the electric heating plate.we obtain the Brillouin optical power negative exponentially rised during the heat dissipation process and linearly dropped during heating.By changing the mode volume area or ambient temperature respectively,we achieve the control of Brillouin micro-laser output power.which provides a new idea for the thermal sensing research of micro devices.