Fabrication Of Nanocrystal Containing Optical Fiber And Its Application

Nanocrystals exhibit special properties compared to corresponding bulk crystals,e.g.quantum confinement effect,quantum size effect,and surface plasmon resonant effect and so on,due to their extremely small size.Therefore,they can be applied in many fields,such as display,detection,micro lasers,biological cure,and nonlinear optics etc.However,some nanocrystals have poor stability and their applicable form is too simple,which makes them usually being dispersed in specific solvents or covered with other materials,like liquids,organic solids,inorganic glasses and so on.Inorganic glasses are a kind of metastable material with good optical,thermal,and mechanical properties.These properties make glass a widely used material in optical communication filed.But the disordered structure of glasses shows relatively small nonlinear effect and makes the possibilities of nonradiation very high,emitting centers in glasses are always in the state with low emission efficiency,while nanocrystals with ordered structure can provide good environment for the emission and other own special properties.In order to combine all these good properties in one material,glasses containing nanocrystals are fabricated which are called glass-ceramics.However,nanocrystals play the role as a nucleation agent in glass,which can degrade the thermal stability of glass against crystallization.Therefore,glasses containing nanocrystals cannot be drawn easily into fibers due to crystallization during fiber fabrication process,which confines the application of glass-ceramics.In this research,we aimed at fabricating glass-ceramic fibers with good optical properties by two methods.On one hand,we fabricated glass-ceramic fiber by applying a fiber fabrication method named melt-in-tube in which the fiber is drawn at the temperature of soften clad glass and molten core glass.Thus,the crystallization of core glass can be prohibited.On another hand,by applying a soft glass with specific composition,the glass can be drawn into fiber at relatively low temperature where the potential barrier for atom migration is very high in the glass.Therefore,the crystallization in core glass can be prohibited for the low velocity of atom movement.The whole research results will be presented next.?1?Precursor glass doped with Er³⁺-Yb³⁺ was prepared by melt quenching method.DSC measurement was performed to decide the heat treatment temperature for crystallization and anneal temperature for stress releasing.Then,the precursor glass was heat treated at different condition to fabricating glass-ceramic containing CaF2 nanocrystals.By applying absorption spectra and XRD measurements,the type and size of crystals were identified.The size of the nanocrystals increases with increasing heat treatment time,which would also degrade the transmittance of glass in visible region.Besides,emission and life time measurement of the glass-ceramic was performed.The enhanced emission and elongated life time show that the rare earth ions are in the crystals at least partially.After drawing the core glass rod into fiber by rod-in-tube method,the residual glass rod and fiber are opaque due to the uncontrollable crystallization.While by applying melt-in-tube method,well-structured and transparent glass fiber was fabricated.EMPA measurement shows no apparent element diffusion between core and clad.In addition,the presence of nanocrystals was confirmed and the size of the crystal ranging from 2 to 5 nm was observed by TEM measurement after heat treatment.What's more,the upconversion emission intensity of the crystallized fiber is greater than that of the precursor fiber under the excitation of 980 nm LD.By analyzing the relationship between emission intensity and pumping power,we concluded that this upconversion emission is a two photon process.?2?Silver ion doped precursor glass was prepared by melt quenching method.DSC measurement was performed to decide the heat treatment temperature for crystallization and anneal temperature for stress releasing.Silver nanoparticles presented after heat treatment,which was confirmed by absorption spectra.With increasing heat treatment duration,the plasmon resonant peak shows a red shift,which was contributed by the increasing silver particle size.Precursor fiber was then prepared by melt-in-tube method.EPMA measurement shows no obvious elements inter diffusion between core and clad.Plasmon resonant peak was also red shifted with increasing heat treatment time.TEM measurement shows that the crystal size is about 5nm in fiber after heat treatment.Great optical nonlinearity of this fiber was also presented.?3?Precursor glass was prepared by melt quenching method.DSC measurement was performed to decide the heat treatment temperature for crystallization and annealing temperature for stress releasing.After drawing the precursor glass rod into core glass rod,CdS quantum dots were formed in the core glass rod.Raman spectral measurement shows that the structure of the glass had been changed after the drawing process and such change is good for confining the growth of quantum dots in the glass.And the size of the quantum dot changed with the time in the furnace during the fabrication process.By drawing the core glass rod and clad tube into fiber,a fiber with good core-clad structure and CdS quantum dots in the fiber core was obtained.And the fiber shows broadband red emission under the excitation of 405 nm LD.Besides,the emission intensity degraded and absorption edge red-shifted with increasing temperature.Finally,the optical nonlinearity of this fiber was presented and discussed.