Fabrication And Performance Research Of Nd³⁺-doped Chalcogenide Glass Microspheres

Glass microsphere has many unique properties such as high quality factor, small mode volume and very narrow spectrallinewidths, which giveitpotential intheapplication fieldrangingfromall-optical-switching, lowthresholdmicrolaser to optical WDMand superhigh sensitivity sensors. Therefore, it gets more and more research attention. The thesis emphasizes the fabrication of theNd3+-doped chalcogenide glass microspheres and their fluorescence and laser output performance. As a novel optical material,chalcogenide glass possess several excellent properties, including good optical transmission in near and mid infrared region（0.5-1μm~12-25μm）, low phonon energy（200-350cm-1）, high refractive index n1（2.0-3.5）, very high nonlinear refractive index n2（100~1000higher than silica）. As a result, chalcogenide glass microsphere has much better confinement for the light inside, lowernonradiativeprobabilitiesand moreobviousnonlinear effect.However, researches on chalcogenide glass microspheres are few and far between for until now. And the chalcogenide glassmicrospheres have been reported are consentrated on the As based passive glass microspheres, such as As2S3and As2Se3glassmicrospheres, which are not environmental. For the active chalcogenide glass microsphere without As element has only demonstratedonly once in2010, except which most researches are focused on the silica or oxide glass. Hence, the thesis will move on researchcovering from the chalcogenide glass optimization of component and concentration of the doped rare-earth ions to the fabrication ofthe chalcogenide glass. And the morphology-dependent resonances and coupling optical spectrum properties will also be studiedfurther.The thesis introduction part mainly analyzes the research history of the glass microsphere. The whole technology about glassmicrosphere, including fabricating method, coupling method, rare-earth doping and its application aredescribed. And properties of thechalcogenideglassandthedevelopment oftheconsequentingrare-earth doped chalcogenideglassmicrospheresat homeandbroad arealso introduced.Thelastpartoftheintroductionproposesthecontent, methodsand significanceofthisstudy.In chapter two, the theory and properties of microsphere resonators are introduced. The optical field distribution of themicrosphere resonators is described according to the geometrical optics and especially, the wave optics. Characteristic equation of theTE and TM mode for the WGMs are constructed respectively, by using the Maxwell equations. Further more, the position andlinewidth of resonaces are also deduced. The properties of the glass microsphere are analysized, including quality factor, propogationconstant and the volume of the WGM mode, which builds the theoretical foundation for the subsequent researches. And this chaptergivesan important guidetomoveon theexperiment.The third chapter firstly introduces the fabrication technology of the Nd3+-doped Ge-Ga-S-CsI chalcogenide glass. Then itsthermal and optical properties are tested, and the process of fabrication for the corresponding Nd3+-doped chalcogenide glassmicrospheres is highlighted. The fabricating process includes the design of the manufacturing device, the milling and sorting of glasspowders crushed from the glass, the melting of microspheres under high tempreture and cooled to the room temperature. At last, thesize distribution and surface quality of the prepared glass microspheres are characterized and this chapter serve the properchalcogenideglassmicrospheresfortheexperimentbelow.In chapter four, the alcohol burner heating and pulling mehod for preparing the silica fiber taper ismainlydescribed. Acompleteset of platform, including fiber taper fabrication, detaching and loss test, is constructed. The experimental results show that thediameters of the prepared fiber taper are between1and2μm, and the surfaces are smooth. A novel technology for taking the fibertaper down from the platform is designed deliberately which can prevent the fiber taper falling apart effectively. And in the followingoptical loss tests manifest that more than86%of the light get through the fiber taper, and losses of the fiber tapers is about0.5dB ingeneral. The dust in the air can be found attached to the fiber taper for the reason of Van der Waals’ force when observed from themicroscopeandtheycan beopticalscatteringpointswhen thelight passesthefiber taper. Asaresult,theprepared fiber taper shouldbeused intheexperiment assoon aspossible.In chapter five, this work explores the optical properties between the Nd3+-doped75GeS2-15Ga2S3-10CsI chalcogenide glassmicrospheresandthesilicafiber taper（1~2μm）couplingsystembased onthecouplingtheory.Thetheoretical modelingresultsshowthat high order WGMs will be excited inside the microsphere at both808nm and1075nm which because of the existence of bigrefractive index contrast between the chalcogenide glass and silica fiber. Coupling results manifest that the microspher made from theglass contain some water is only observed with fluorescence output around1075nm. However, the miciosphere made from the glassdo not contain water is observed with laser output when the pump laser reaches its threshold about tens of mW. And at the same time,we observe that the lasing wavelengths of the microsphere are very unstable and change tremendously. The external environmentfactors such as air flow and vibration of the platform give an effec on the coupling system which make it not such stable. Theexperimental environment shouldbeimproved inthefutureforthecouplingexperimental needstobecarried on withhighstandards.The sixth chapter is the conclusion and outlook. Here, the conclusions of this study are summarized. And at the same time, wepointout thetheexistingproblemsin theexperiment and theprospectsshould beimproved in thefuture.