Fabrication And Characterization Of Active Whispering Gallery Mode Microsphere/disk Resonators Operating On The Near-infrared Spectrum

Spherical or disk-like optical Whispering Gallery Mode（WGM）resonators have many desirable physical/optical properties,such as low structural complexity,high-quality factors（Q-factors）,small mode volumes,and compatible to modern fiber/waveguide devices,and thus find many interesting applications in the fields of low-threshold lasers,nonlinear optics,and narrow bandwidth filters.In this work,we present the fabrication and characterization of microsphere/microdisk WGM resonators fabricated with various interesting infrared materials,such as chalcogenide glass and tellurite glass.By doping the resonators with active dopant ions and coupling them with micro fiber tapers,we demonstrated that when pump powers were increased beyond certain thresholds,sharp laser lines can be obtained from those resonators.This dissertation includes the following two parts:（1）Fabrication of microsphere resonators with the chalcogenide glass of Ge-Ga-Sb-S（2S2G）.This 2S2G glass is selected because it has a wide transmission window and a low softening temperature（780 ℃）.It is also more environmentally friendly and more resistant to crystallization problem than other chalcogenide glasses.We doped the 2S2G glass with Tm³⁺-Ho³⁺ions and crushed the base glass material into powders.We then processed the glass powders with the classic droplet method,so that those powders can be transformed into microspheres via surface tension.Microspheres fabricated in this work have diameters of50-250μm and their typical quality factor is about 10⁵.A microsphere with a diameter of205.82μm was selected for further optical characterizations.An 808 nm semiconductor laser was used as the pump source and a 1.7μm diameter fiber taper was used as the coupling mechanism.Apparent WGMs in the wavelength ranging from 1.7-2.1μm can be obtained from the microsphere/fiber taper coupling system and when the pumping power increased beyond 0.848 m W,sharp laser lines at 2080.54 nm can be obtained from the coupling system.（2）Fabrication of microdisk resonators with the tellurite glass of Te O₂-Zn O-Na₂O.This tellurite glass is selected because it can be thermally processed in air and it has a low softening temperature（～370 ℃）.We doped the tellurite glass with Nd³⁺and Tm³⁺and then fabricated microspheres with it.We then used a home-made thermal pressing method to transform those microspheres into microdisks.Diameters of microdisks fabricated in this work are ranging from 100-400μm,the minimum thickness of those microdisks is about 8μm,and the typical quality factor is～10⁵.An Nd³⁺doped tellurite microdisk with a diameter of 105.74μm and a thickness of 10.4μm was selected as the experimental target and was coupled with a1.7μm diameter fiber taper.An 808 nm semiconductor laser was used as the pump source.Apparent WGM patterns can be obtained from the microdisk/fiber taper coupling system and when the pumping power exceeded 1.364 m W,laser modes can also be obtained.Similarly,a Tm³⁺doped microdisk（diameter:104.36μm and thickness:15.86μm）was selected for optical characterizations.We show that when the pumping power increased beyond 1.306 m W,laser modes at～1.9μm can be obtained.