Lattice vibration and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate

Raman scattering and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate were examined. The A₁(TO) modes appear in E symmetry spectrum of the doped lithium niobate. Their intensities vary with different dopings. In the spectrum of z(yy)x geometry, the properties of the lowest-frequency E(TO) mode of the Cr-doped lithium niobate are different from those of pure, Co- and Fe-doped lithium niobate. The intensity of the A₁(TO) mode at 637cm^-1 I is decreased in doped lithium niobate compared with the pure crystal. We attribute these properties to both the photorefractive effect which is enhanced by dopants and to the different occupation of the doping ions. A light climbing effect was observed in Co- and Cr-doped lithium niobate for the first time. A higher photodamage threshold and quicker light climbing speed were found in Co- and Cr-doped lithium niobate in comparison with the light climbing effect in the Fe-doped lithium niobate. The results from the photoinduced light scattering experiments were compared with those from a Raman spectroscopic study.     

Synthesis, structure and ferroelectric property of a new niobate: Sr6CrNb9O30

A new niobate Sr₆CrNb₉O₃₀ was found in the ternary system SrO---Cr₂O₃---Nb₂O₅. The transparent crystal which has a green color and a need-like shape can be grown by the flux method. The crystal structure was determined by x-ray diffraction analysis and dielectric measurement, and it belongs to the orthorhombic tungsten bronze structure at room temperature with space group Cmm2, and unit cell parameters A=1.7505(4) nm, B=1.7510(1) nm, C=7.768(4)nm, Z=4. Dielectric constant measurement show that Sr₆CrNb₉O₃₀ has two phase transitions, paraelectric to ferroelectric at 110°C and ferroelectric to ferroelastic at 205°C.     

Inhomogeneity of composition in near‐stoichiometric LiNbO3 single crystal grown from Li rich melt

A near‐stoichiometric LiNbO₃ single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li₂O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO₃ crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation Enthalpy Calculation of Oxygen Vacancy Defect in Doped Lithium Niobate Crystals

The relationship between temperature and oxygen vacancy concentration is deduced in this paper. Based on the data of thermal weight-loss experiment, the formation enthalpies of congruent and several doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping valence-changeable ions. The experimental results were discussed and a new reduction process of the photorefractive LN crystal at a relatively low temperature was proposed, and the reduced crystals showed a good effect in practical use.     

近化学计量比掺镁铌酸锂晶体的抗光折变性能

应用气相传输平衡技术,我们获得了3种近化学计量比掺镁铌酸锂晶体,晶体的掺镁量接近我们以前提出的第二阈值.在我们实验室所能达到的最大光强26 MW/cm2照射下,在所有近化学计量比掺镁铌酸锂晶片中没有观察到光斑畸变,该光强比同成分铌酸锂晶体所能承受的光强高6个量级,为目前已报道的铌酸锂晶体之最.应用双光束全息写入法测得掺1.0 mol; Mg近化学计量比铌酸锂晶体的光折变饱和值仅有4.6×10-7,比同成分铌酸锂晶体小两个量级,从已有实验数据推测,该晶体的抗光折变能力应当比同成分铌酸锂晶体高9个量级以上.     

液相外延法制备LiNbO3薄膜的研究和进展

讨论了液相外延法制备LiNbO3薄膜过程中,衬底和助熔剂的选择对LiNbO3薄膜制备的影响及掺杂改性问题,简要地介绍了LiNbO3薄膜的一些性能及光学应用.研究表明,目前可用液相外延法在LiTaO3、掺镁(5mol;)的同成分LiNbO3及纯的同成分或近化学计量比LiNbO3单晶衬底上制备出具有较高光学质量的LiNbO3薄膜.讨论了液相外延法制备LiNbO3薄膜过程中存在的主要问题、发展前景及今后的研究方向.     

Mach-Zehnder电光波导调制器啁啾的研究

在光纤通信系统中,调制器的啁啾参数是衡量调制器性能的重要参数之一.为了深入研究铌酸锂M-Z结构外调制的机理,导出了Mach-Zehnder结构外调制方式调制器的啁啾参数表达式,研究表明该结构调制器频率啁啾不为零,而且调制器的直流偏置漂移对啁啾的影响很小.详细讨论了影响啁啾参数的因素,分析了直流消光比、外加信号以及直流偏置漂移对器件啁啾参数的影响.分析结果表明,利用负啁啾可以改善系统的色散特性.     

级联二阶非线性铌酸锂全光开关的研制

以基于准位相匹配和频与差频级联二阶非线性[X^(2)：X^(2)]基础上的全光开关的理论分析作指导,进行了周期极化铌酸锂晶体(PPLN)和退火质子交换光波导(APE)的实验制备,利用所研制的PPLN-APE器件,以自行研制的工作波长为1．54μm的被动调Q掺钴铝酸镁激光器作为控制光源,以工作波长为1．5μm的连续二极管激光器为信号光源进行了级联二阶非线性全光开关实验。当控制光峰值功率为3kw,信号光功率为1mW时,实现13％的开关效率,分析了进一步提高全光开关性能的途径。     

飞秒激光烧蚀LiNbO3晶体的形貌特征与机理研究

采用了不同能量的单脉冲和多脉冲飞秒激光对LiNbO₃晶体进行烧蚀，并刻蚀了表面衍射型光栅.通过扫描电镜和原子力显微镜观察了烧蚀点的形貌特征，首次发现利用单束飞秒激光脉冲对LiNbO₃晶体烧蚀，可以得到超衍射极限的烧蚀点，当聚焦光斑直径约为2μm、能量为170nJ的单脉冲飞秒激光作用时，烧蚀点的直径约为400nm，100nJ，17个脉冲作用时烧蚀点的直径约为800nm.同时可以观察到在能量较低的多脉冲飞秒激光作用下， LiNbO₃晶体呈现出大约200nm周期性分布的波纹状结构.实验结果表明，选择合适参数的飞秒激光脉冲可以对LiNbO₃晶体进行超衍射极限加工，这对于利用飞秒激光制作LiNbO₃基质的微纳光电子器件有十分重要的意义.     

信息时代的铌酸锂晶体:进展与展望

铌酸锂晶体具有非线性效应、电光效应、声光效应、光折变效应、压电效应与热释电效应等多种物理特性,在表面声波器件、光电器件、声光器件等方面获得广泛的应用.经历了六十多年的发展,铌酸锂晶体历久弥新,随着材料特性的不断开发,新功能、新器件、新应用层出不穷,尤其是铌酸锂单晶薄膜在薄膜滤波器、集成光电器件等领域的性能具有明显优势,...