Functionalized Silica Optical Microcavities And Their Applications

Due to advantages of low optical absorption and easy fabrication process,silica is an ideal candidate for fabricating the ultrahigh-quality(Q)factor microcavity.Due to its ultrahigh Q factor and small mode volume,the silica whispering gallery mode(WGM)microcavity has a broad prospect in many applications including high sensitivity sensing,microlaser,nonlinear optics,cavity optomechanics and cavity quantum electrodynamics.However,the silica microcavity still has several challenges in its applications:How to improve the Q factor of the erbium doped silica microcavity;How to realize efficient tuning of the ultrahigh Q silica microcavity.In the thesis,the functionalized silica WGM microcavity was investigated.All-optical control of the ultrahigh Q silica microcavity was realized and its applications in the microlaser and nonlinear optics were broadened.The research contents include:all-optical control of the ultrahigh-Q silica microbottle cavity and its application in the controllable electromagnetically induced transparency effect;tunable microlaser in the ultrahigh-Q erbium-doped microbottle cavity;low threshold tunable Brillouin and Raman microlasers in the functionalized microbottle cavity;controllable optical frequency comb based on the hybrid microsphere cavity;polarization beam splitter and magnetic field sensor based on the optofluidic ring resonator.The thesis is divided into following several sections:(1)Based on the strong photothermal effect of iron oxide nanoparticles,an all-optical control scheme for the ultrahigh-Q microbottle cavity was realized.WGMs were away from nanoparticles,which meant that the microcavity could maintain its ultrahigh Q factor during the tuning process.The tuning range of 85.9 GHz(0.68 nm)was achieved.A spherical end was fabricated by optimizing the microcavity structure,hence more iron oxide nanoparticles could be coated in this area.The tuning range of 282.32 GHz(2.25 nm)was achieved based on the simple and stable device.Furthermore,the controllable electromagnetically induced transparency effect was realized in coupled tunable hybrid microbottle cavities.A transparency window bandwidth of 2.3 MHz and a whole spectrum tuning range of 71.52GHz were realized.(2)A new erbium-doping method was proposed,which avoided cracks and defects,and the ultrahigh-Q erbium doped microbottle cavity was fabricated.The nanoparticle-coating method was improved,which made nanoparticle-coating area more controllable.The Q factor of 5.2×10~7 was achieved based on the simple and repeatable method,which was better than those achieved from the conventional sol-gel method.Due to its ultrahigh Q factor,the lasing threshold of 1.65 m W was achieved through nonresonant pump.Due to its excellent tuning performance,a tuning range of 4.4 nm was achieved.Besides,tunable Brillouin and Raman microlasers with low thresholds were also realized based on the Stimulated Brillouin and Raman scattering effects.Tuning ranges of 2.68 nm and 2.32 nm were achieved,respectively.(3)Based on the functionalized microsphere cavity,controllable Kerr frequency comb and Raman-Kerr frequency comb were realized.Iron oxide nanoparticles cannot influence the Q factor and group velocity dispersion of WGMs,and the control light could transmit through the fiber stem and arrive the end of microsphere,which meant that the control light could be absorbed effectively by nanoparticles.The optical parametric oscillation with an ultralow threshold of 0.42 m W was achieved in the microsphere cavity with a diameter of248?m.The controllable Kerr frequency comb was also realized.Besides,with a help of the Raman laser,the Raman-Kerr frequency comb with a comb span of 164 nm was achieved in the microsphere cavity with a diameter of 139?m,when the pump power was only 954?W.A comb line tuning range of 2.67 nm was achieved.(4)The polarization beam splitter and magnetic field sensor were realized in the optofluidic ring resonator.Based on the birefringent effect of the optofluidic ring resonator,a tunable polarization beam splitter was proposed.The extinction ratios in the through port and the drop port were 38 d B and 20 d B,respectively.The resonance tuning range of 7.02nm was achieved by replacing the fluid with different refractive indexes(RIs).The magnetic fluid was filled into the core of the optofluidic ring resonator.Based on the magnetically tunable RI effect,the magnetic field sensing with a sensitivity of 75.7 pm/m T was realized.