Structures And Optical Properties Of Multi-Component Transition Metal Oxide Glass

The rapid development of information technology requires a higher-capacity telecommunication system.Our country has put forward the“Broadband China”and has taken broadband telecommunication as a strategic key for the country’s development.In the telecommunication system,optical fiber communication plays a crucial role and its capacity depends on the gain bandwidth of fiber optical amplifier（FOA）.Currently,erbium-doped fiber amplifier（EDFA）can only provide³5 nm gain bandwidth due to the narrow-band luminescence properties of rare earth ions,which limits the capacity of telecommunication system.To overcome this limitation,the most effective strategy is to explore novel gain materials which can potentially give broadband optical amplification.Especially,photonic materials with d-d transitions and/or nonlinear Raman gain have been widely studied for their potential applications as broadband gain materials.Despite enormous research efforts,the construction of gain materials with broadband and efficient optical amplification properties remains an arduous task.This thesis focuses on the design and fabrication of novel gain materials for broadband optical amplification.Firstly,the heterogeneous structure of multi-component transition metal oxide glass system was studied.By control of the the structure and nanocrystallization,tunable and broadband near-infrared luminescence are successfully achieved in Ni²⁺-doped glass-ceramics.Secondly,the Raman scattering characteristics of multi-component transition metal oxide glass system are studied.It can be found that the large polarizability and unique connective structures of transition metal ions inside glass allow for generation of large Raman intensity and broadband Raman bandwidth.Thirdly,the multi-component transition metal oxide glass fiber is fabricated by“molten core”method.Detailed research contents and research results are as follows:（1）Researches on the structures of multi-component transition metal oxide glass:Molecular dynamics are used to study the structures of the glass system that heavily doped with Ta₂O₅.The bond distribution,bond length,and coordination number are calculated.It can be found that the nanoscale heterogeneities enriched with Ta or Si/Al elements are homogeneously distributed inside glass.The heterogeneous structures obtained with different cooling rates are also simulated,and the results indicate that heterogeneities are originated from the the liquid-liquid phase separation during melting.The presence of heterogeneities inside glass is further validated by using the high angle annular dark field scanning transmission electron microscopy（HAADF-STEM）technique.（2）Researches on multiphase glass-ceramic doped with Ni²⁺derived from multi-component transition metal oxide glass for broadband luminescence:The heterogeneities of multi-component tantalum silicate glass provide the possibility to precipitate multiple nanocrystals.After heat-treatment,the LiTaO₃ and LiAlSi₂O₆ nanocrystal are successfully precipitated from the glass matrix.Then Ni²⁺ion is selected as luminescence center to dope into this glass-ceramics.It is found that Ni²⁺ions are incoporated into these two types of nanocrystals.Ultra-broadband near-infrared luminescence can be obtained by combining the luminescence bands of Ni²⁺at different nanocrystals.By optimizing the crystallization process especially the heat treatment duration,the ultra-broadband luminescence（up to 480 nm）with flat spectral shape can be achieved.（3）Researches on phase control in multi-component transition metal oxide glass doped with Ni²⁺for tunable broadband luminescence:The heterogeneities of multi-component tantalum silicate glass provide the possibility to control the crystallization process.Firstly,the investigation on glass structures indicates that heterogeneities are homogeneously distributed inside glass matrix with nanometer size.The crystallization kinetics is used to analyze the crystallization mechanism.It is found that Ta elements enriched region serves as crystal nucleus for Ta₂O₅ nanocrystals phase,and the growth of nanocrystals shows diffusion dependence.The unique structures of this glass allow us to obtain glass-ceramics with 56%crystallinity（mass percent）and 85%transmittance in the near-infrared region.Secondly,by substitution of network modifier with larger diffusivity ions,another two types of nanocrystals（LiTa₃O₈ and LiTaO₃）can precipitate inside glass phase.Thirdly,Ni²⁺ion is selected as luminescence center to dope into this glass-ceramics.Because the precipited LiTa₃O₈ and LiTaO₃ nanocrystals can provide different crystal field strength for Ni²⁺dopant,the fabricated glass-ceramics present tunable and ultra-broadband near-infrared luminescence which covers the whole telecommunication band.（4）Researches on Raman scattering properties of multi-component transition metal glass:The transition metal ion such as Nb⁵⁺has large polarizability and forms various unique structure units.This potentially provides opportunity to achieve strong Raman scattering.Firstly,various niobium germanate glass systems are designed and fabricated by introducing large amount of Nb₂O₅ into germanate matrix.It is found that the distorted[NbO₆]octahedrons inside glass matrix are interconnected with each other by corner-or edge-shared form.This leads to large Raman intensity and broadband Raman gain.The Raman gain coefficient and Raman gain bandwidth are calculated to be around 50×10^-13 m/W and 300cm^-1,respetively.Secondly,the structure change of this glass during crystallization process is investigated.The results show that the connective structures of[NbO₆]octahedron changes from edge shared form to corner shared form.Thirdly,by optimization of the heat-treatment process,the structure change of niobium germanate glass-ceramics can be controlled and the large Raman intensiy and flat Raman gain are successfully achieved.（5）Researches on construction of multi-component transition metal oxide glass fiber and fabrication of microchannels by space-selective control of phase separation in glass:Firstly,the multi-component transition metal oxide glass fiber is fabricated by using the“molten-core”method,which can prevent the occurance of uncontrollable crystallization during fiber drawing process.Owing to the fast fiber drawing velocity,the inter-diffusion between core and cladding is effectively reduced.After heat-treatment,LiTaO₃ and Li AlSi₂O₆ nanocrystals are precipitated from the fiber.The glass-ceramics fiber shows wavelength conversion function,due to the frequency-doubled effect of LiTaO₃ nanocrystal phase.Secondly,an effective strategy for fabrication of microchannels inside glass is proposed based on space-selective control of phase separation inside glass induced by femtosecond laser.The proposed method allows for fabrication of microchannels with millimeter scale and a uniform cross section.