Research On Ultrahigh-quality-factor Rare-earth-doped Microcavities And Their Lasing Characteristics

Whispering-gallery-mode（WGM）microcavities with ultrahigh quality（Q）factor and small mode volume are attractive for their potential applications in high-precision sensing,nonlinear optics,cavity optomechanics and microlasers.Rare earth（RE）elements with high stability,high photoluminescence quantum yield and abundant spectrum bands are excellent luminescent materials.If we can homogeneously dope rare earth elements into WGM microcavities without severely degrading their intrinsic Q factor,it is expected to realize low-threshold and narrow-linewidth microlasers,covering multiple lasing bands.In this thesis,the RE-doped WGM microlasers were investigated.The main research contents include:the preparation of ultrahigh-Q RE-doped silica microsphere cavities,low-threshold and narrow-linewidth laser in 1.5μm band,erbium-based single-mode lasing in 1.5μm band via loss engineering,RE-based multi-band,high-order upconversion and white upconversion continuous-wave（CW）lasing at room temperature（RT）.The specific researches of the thesis are as follows:（1）A RE doping method by polymer-assisted thermal diffusion was proposed.Based on this method,RE-doped silica microsphere cavities can achieve intrinsic Q factor at 10⁸level,effective doping concentration at 10¹⁸/cm³level,and lasing in 1.5μm band with low threshold and narrow linewidth.（2）A loss-engineering-based method for achieving erbium-doped single-mode microlasers in 1.5μm band was proposed.Thulium is codoped into microcavities as a loss modificator for erbium,suppressing low-gain competing modes,achieving mode-hopping free single-mode lasing in 1.5μm band with high side-mode suppression ratios exceeding50 d B,showing excellent performance and robustness.This mode suppression mechanism is further verified in Rhodamine-doped polymer microbottle cavities,indicating that it can be universal for different gain materials and cavity structures.（3）Based on an erbium-ytterbium-codoped microsphere,simultaneous lasing in ultraviolet,visible and near-infrared bands at RT was realized by pumping a 975-nm CW laser.All the lasing bands have lasing thresholds below one milliwatt,while lasing wavelength range is up to 1170 nm.The optical spectrum acquisition under Purcell effect is analyzed by theoretical calculation and experiments.The annihilation of Purcell-enhanced spontaneous emission peaks at an increased pump power is used to further confirm lasing onset.（4）Based on an erbium-doped microsphere,high-order upconversion lasers were realized.By pumping a 1540-nm CW laser,380 and 410-nm-band lasers were realized at RT with lasing thresholds below one milliwatt,which correspond to five-and four-order upconversion lasers,respectively.（5）Based on a thulium-erbium-ytterbium-codoped microsphere,white upconversion lasers were realized.By pumping a 975-nm CW laser,red,green and blue lasers were achieved at RT.At 8.8-m W pump power,the chromaticity（0.297,0.323）of the microfiber-dropped laser is very close to that of the standard white light.