Optical Application Research Based On High-Q Quartz Microspheres

We know that the sound in the Temple of Heaven can travel a great distance along its inner wall.Similarly,photons possessing much short wavelength can also propagate along the equatorial plane through total internal reflection on the inner surface of the whispering chamber microcavity.When the circulating length of the light wave equals to an integer multiple of the wavelength of the photon,a stable resonance with ultra-high photon density can be formed in the micro-cavity due to the ultra-long photon life and small mode volume,and strongly enhances the light matter interaction even if the pump power is small.The microsphere cavity has been widely used for the studies of nonlinear optics,high sensitive sensing,and ultra-narrow linewidth optical filtering and low threshold lasing etc.In this paper,the applications of high Q quartz microspheres in displacement sensing and narrow linewidth reflection filtering are proposed and studied.The detailed research works are presented as follows:(1)Theoretical studies on the influences of the resonant modes induced by metal interferenceThe interference effects of metal on the resonant mode of the microcavity are studied and analyzed based on the full wave simulations by finite-difference time-domain(FDTD)method,including two-dimensional metal displacement disturbance and three-dimensional metal displacement disturbance.When the metal morphology is changed,namely tuning the perturbation area of metal on the resonances;the variations of resonance field distribution,Q factor,and resonant wavelength at different conditions are obtained.The results show that:(1)The "Compression" effect of high Q resonance mode is observed when the metal closes to the microcavity,and the strength of the field near the metal is significantly weakened;(2)As the metal approaches,the loss caused by the surface plasma increases,and the resonance Q value decreases;(3)The position of high-Q resonance mode shifts to the short-wave wavelength(blue shift)while the metal is approaching to the microcavity,or the interaction area between metal and microcavity increases.(2)Experimental studies on the displacement sensing based on Brillouin microsphere laserWe firstly propose a packaging method of silica microsphere with a fiber taper in order to realize a stable performance of Brillouin microsphere laser,namely both the taper of fiber(TOF)and the microsphere cavity are fixed on the same "U" shaped model.The coupling system is placed in a clean plastic box to avoid environmental contamination.In addition,based on the theoretical simulation of the influence of metal probes on the distribution of the microcavity field,the experiments are performed by introducing a metal probe near the microsphere cavity to disturb the performance of Brillouin microlaser.From the thermal properties of the Brillouin laser in the quartz microsphere cavity,it can be known that the wavelength blue shift will increase the output power of the laser.Therefore,when the metal probe approaches the microsphere cavity,the Brillouin laser power is experimentally observed to increase.Experimentally,the results of theoretical predictions were obtained,providing a feasible solution for the displacement sensing of micro-lasers.(3)Single frequency passively Q-switched fiber lasers realized by employing microsphere as a reflecting mirror with narrow linewidthSome experiments are done to realize a passively Q-switched the single frequency laser by employing a microsphere cavity.Here,the erbium-doped fiber functions as the gain medium,the carbon nanotubes functions as the satrated absorber,and the microsphere functions as a narrow linewidth reflection mirror.A stable single-frequency Q-switched laser with a wavelength of 1549.02 nm is realized.The repetition frequency varies from 156.25 kHz to 316.46 kHz,the narrowest pulse width is 0.4 p,s,and the SNR of the single-frequency laser is 49 dB with a line width of less than 50 kHz.