Ultralow-threshold Neodymium-doped Microsphere Lasers On A Silicon Chip

As essential optical components,optical microcavities have been widely applied in both fundamental and applied studies,such as low threshold microlasers,nonlinear optics,cavity optomechanics,cavity quantum electrodynamics,biosensing and so on.Microsphere cavities,which have the advantage of ultrahigh quality factors and small mode volumes,have become excellent cavities for achieving narrow linewidth and low threshold lasers.In this thesis,we have studied the fabrication of this whispering-gallery-mode microcavity and its application for microlasers.We have obtained ultralow-threshold neodymium-doped microsphere lasers on a silicon chip by the sol-gel method.In our work,to fabricate the chip-based Nd3+-doped microsphere cavities,we prepared the silica sol-gel film with a thickness of approximately 1.3 μm.During the sol-gel process,Neodymium(Ⅲ)nitrate hexahydrates(Nd(NO3)3·6H2O)with different doping concentrations were added into the solution.Then,with the combination of photolithograph,buffered HF wet etching,XeF2 dry etching and CO2 laser reflow,the Nd3+-doped microsphere structures were finally formed.We used a narrow-linewidth tunable laser operating around the 780 nm band to resonantly pump the Nd3+-doped microspheres,and laser spectra at 900 nm band and 1060 nm band were observed,with thresholds of 2.4 μW and 1.2 μW respectively.