LiNbO3:Fe晶体中光写入波导时折射率的变化规律

研究了利用光辐照法制作光折变波导时LiNbO3:Fe晶体中折射率变化的规律.分别采用波长为6328nm和532nm的寻常偏振和非常偏振的细激光束和片状激光束，在LiNbO3:Fe晶体中进行了写入波导实验.研究表明，制作波导的写入光宜采用寻常偏振光.在利用由光束辐照LiNbO3:Fe晶体形成的正折射率变化区域作为波导结构时，必须严格控制辐照时间.否则，由于长时间光辐照会带来较强的噪音栅以及折射率变化区域会发生扩展，而难以形成优 质波导.利用片光在“三明治”方式辐照下，以小曝光量制作波导时，可以避免噪音栅的 关键词： 光致折射率变化 光折变波导 光辐照法 LiNbO3:Fe晶体     

LiNbO3∶Fe晶体中光写入阵列平面光波导的实验实现

采用两束相干平行光形成的干涉光场辐照LiNbO3∶ Fe晶体,通过光折变效应在晶体中写入了阵列平面光波导.分别采用马赫-曾德干涉仪光路和光栅衍射法测量了阵列平面光波导的横向折射率分布和周期,并对所写入的阵列平面光波导进行了初步的导光测试.实验结果表明,用这种方法写入阵列平面光波导简便可行.     

LiNbO_3:Fe晶体中光写入平面光波导的导光特性研究

从光折变效应的单中心模型和载流子的光伏迁移机理出发给出了高斯片光在LiNbO3:Fe晶体中导致的折射率变化分布的解析表达式 .利用片光以“三明治”辐照方式在LiNbO3:Fe晶体中写入了平面光波导结构 .用切片干涉法测量了波导区的折射率分布 ,并对波导进行了简单的导光测试 .根据射线方程以及波导的折射率分布对光写入波导的导光特性进行了模拟计算分析 .研究结果表明 ,在LiNbO3:Fe晶体中光写入光波导是可行的     

LiNbO3:Fe晶体中光写入平面光波导的导光特性研究

从光折变效应的单中心模型和载流子的光伏迁移机理出发给出了高斯片光在LiNbO3:Fe晶 体中导致的折射率变化分布的解析表达式.利用片光以“三明治”辐照方式在LiNbO3:Fe晶 体中写入了平面光波导结构.用切片干涉法测量了波导区的折射率分布，并对波导进行了简 单的导光测试.根据射线方程以及波导的折射率分布对光写入波导的导光特性进行了模拟计 算分析.研究结果表明，在LiNbO3:Fe晶体中光写入光波导是可行的. 关键词： LiNbO3:Fe晶体 光辐照法 平面光波导 导光特性 高斯片光     

飞秒激光加工铌酸锂晶体：原理与应用

由于具有超短的脉冲宽度和极高的峰值强度,飞秒激光微加工是一种有效的材料加工方法, 已广泛应用于光子集成器件的加工。铌酸锂晶体具有优异的电光、非线性光学和压电特性,是集成 光学和导波光学中常见的材料。本文综述了飞秒激光对铌酸锂晶体的处理,重点介绍了飞秒激光加 工的物理原理及其制备的铌酸锂基光子器件的最新进展。飞秒激光技术使铌酸锂晶体在微纳光子学 领域具有广阔的应用前景。     

掺杂铌酸锂薄晶体光爬行耦合

实验研究了掺杂ＬｉＮｂＯ３薄晶体中非直接相交的两束光之间大角光致散射的光爬行耦合现。研究了相同材料制备的厚度不同样品的二波和四波耦合的成像质量存在差异的原因。     

白光在LiNbO3∶Fe晶体中写入的任意折射率分布光波导

在理论分析LiNbO3∶Fe晶体中光致折射率变化分布与写入光的强度分布之间关系的基础上，提出了一种在该晶体中写入具有任意折射率分布光波导的新方法.利用由白光经电寻址空间光调制器得到的强度分布不同的片光辐照晶体，分别写入了折射率呈误差函数分布和平方律分布的光波导结构.采用干涉法测量了晶体中的光致折射率变化，并用推导出的折射率变化分布解析表达式很好地拟合了测量数据.实验结果表明，该方法是可行的.利用白光光源结合高分辨率的空间光调制器有望在多种光折变材料中制备出具有任意折射率分布的高质量光波导.     

m线法研究掺杂LiNbO_3晶体波导基片的光损伤

采用ｍ线法研究了掺杂ＬｉＮｂＯ３晶体波导基片的光损伤，发现抗光损伤能力依次为Ｍｇ：ＬｉＮｂＯ３、ＬｉＮｂＯ３、Ｆｅ：ＬｉＮｂＯ３（氧化），Ｆｅ：ＬｉＮｂＯ３（还原）。对于同样材料，质子交换光波导的抗光损伤能力高于钛扩散光波导。     

掺镁铌酸锂质子交换光波导光学性能的研究

本文用质子交换反应在5mol％MgO:LiNbO_3晶体中引起了e光折射率的增加,晶体中MgO的存在并不影响LiNbO_3质子交换光波导阶跃型折射率分布的特点。用常规的质子交换法制备的MgO:LiNb·O_3波导存在着损耗大和有效折射率不稳定的缺点,经过退火处理后,这些缺点可明显地得到改善。     

LiNbO3：Fe晶体三维全息最佳曝光时间研究

对LiNbO3：Fe晶体在三维体全息记录过程中出现的噪声逐渐放大,最终对记录图像产生影响的机制进行探究．通过实验对噪声光强度变化规律进行了定量研究,并运用光感应光散射与二波耦合的能量转移理论,解释了体全息记录中噪声光的产生和放大的机理,提出优化方案．     

Optical waveguides in LiNbO<Subscript>3</Subscript> and stoichiometric LiNbO<Subscript>3</Subscript> crystals by proton exchange

The formation of optical planar waveguides in LiNbO₃ and stoichiometric LiNbO₃ crystals by proton exchange was reported. The prism-coupling method was used to characterize the dark-line spectroscopy at the wavelength of 633 and 1539 nm, respectively. The mode optical near-field outputs from proton-exchanged LiNbO₃ and SLN waveguides at 633 nm were presented. The mode field from stoichiometric LiNbO₃ (SLN) waveguide is lighter and more uniform than that from LiNbO₃ waveguide, which means the quality of the waveguide in SLN crystal is better than that of the LiNbO₃ waveguide. For proton-exchanged LiNbO₃ waveguides, the evolution of the refractive index profile with annealing was presented. The disorder profiles of Nb atoms in proton-exchanged LiNbO₃ waveguides were obtained by Rutherford backscattering/channeling technique. It is shown that the longer the exchange time, the larger the displacement of Nb atoms. Supported by the National Natural Science Foundation of China (Grant No. 10475052) and the Scientific Research Start-up Financing of Qufu Normal University     

Growth and optical properties of Hf,Ce co-doped lithium niobate crystals

In this paper, a series of Hf,Ce co-doped lithium niobate crystals with various HfO₂ concentrations were grown by Czochralski method. The ultraviolet-visible absorption spectra and the infrared transmittance spectra were measured to study defect structure of the crystals. The optical damage resistance was measured by the transmitted facula distortion method. The results showed that the optical damage resistance of Hf:Ce:LiNbO₃ was greatly improved when the Hf-doping concentration was above 4 mol%.     

Femtosecond laser micromachined optical waveguides in LiTaO3 crystal

By using femtosecond laser micromachining, optical wave guides in both depressed cladding and dual‐line configurations have been produced in LiTaO₃ crystal. The guiding properties and the thermal stability have been investigated for both geometries, which exhibit different performance. Depressed cladding waveguides support guidance along both extraordinary and ordinary index polarizations, while dual‐line waveguides support only extraordinary index polarization. Thermal annealing has been proved to be an effective method to reduce the propagation losses. For the cladding waveguide, the lowest propagation loss was as low as 0.38 dB/cm after the annealing treatment at 400 °C. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The dielectric behaviour of doped near-stoichiometric lithium niobate in the terahertz range

The dielectric properties of near-stoichiometric LiNbO₃:Fe and LiNbO₃:Ce single crystals have been investigated using terahertz time domain spectroscopy in a frequency range of 0.7-1.6 THz at room temperature. When coupled with an applied external optical field, obvious photorefractive effects were observed, resulting in a modulation of the complex dielectric constant for the crystals. The variation in refractive index, |Δn|, had a linear relationship with the applied light intensity, accompanied by a step-like decrease at high intensity. The findings were attributed to the internal space charge field of the photorefraction and the light-induced domain reversal in the crystals.     

飞秒激光制作铌酸锂光波导的研究

针对Z切割铌酸锂晶体在中心波长为800 nm、重复频率为76 MHz的飞秒脉冲激光下,利用放大倍数为40、数值孔径为0.65的会聚透镜聚焦,研究了扫描速度和扫描次数的变化对刻写光波导结构的影响,分析了波导结构变化的原因,并测试了1×2光波导功分器的通光性能.实验结果表明:在采用横向扫描、聚焦深度为350~400 μm、扫描速度为100 μm/s和激光功率为250 mW时,获得较理想的铌酸锂光波导,1×2光波导功分器的输出功率分布基本达到均分.     

Theoretical expression for change of extraordinary refractive index in annealed proton exchanged LiNbO3 optical waveguides

A general expression for the change in extraordinary refractive index of the annealed proton exchanged LiNbO₃ waveguide has been deduced. The expression deduced explains the experimental results of decrease in change of extraordinary refractive index with annealing. The effect of annealing time has also been incorporated following Cao's model (Cao, Ramaswamy, Srivastava, J. Lightwave Technol. 10 (1992) 1302–1313). The concentration profile of protons in the annealed waveguide has been deduced theoretically, which is consistent with the previous results. The spontaneous polarization has been considered as the central mechanism for change in extraordinary refractive index due to proton exchange with annealing.     

Temperature dependence of linear electrooptic coefficients r 113 and r 333 in lithium niobate

A new method of determination of individual linear electrooptic coefficients is proposed. The technique is based on the dynamic polarimetric measurements and takes into consideration the temperature dependences of ordinary and extraordinary refractive indices. Results obtained for the electrooptic coefficients r₁₁₃ and r₃₃₃ in LiNbO₃ are presented. The coefficients are found to increase significantly within the considered temperature range 25-200°C. The temperature dependences of the intrinsic coefficients m₁₁₃ and m₃₃₃, defined in terms of the induced polarisation, are considered as well.     

Studies of the optical spectra and spin-Hamiltonian parameters for the trivalent ytterbium ions in lithium yttrium fluoride crystals

In this paper, the crystal field (CF) levels and spin-Hamiltonian (SH) parameters (g factors g _∥ and g _⊥ and hyperfine structure constants A _∥ and A _⊥) of the rare-earth ion Yb³⁺ in lithium yttrium fluoride crystals are calculated under D _2d point symmetry assumption. Two main methods are used in the calculation to study the SH parameters: one is the perturbation theory method and the other is the complete diagonalization (energy matrix) method (CDM). Comparing the calculated results with the experimental data, we can see that the CDM is more effective to calculate the SH parameters. In addition, the CF J-mixing of all excited-state multiplets into the ground-state multiplet ²F_7/2 is considered. The validity of the calculated results is discussed.     

Widely tunable high power OPO based on a periodically poled MgO doped lithium niobate crystal

An optical parametric oscillator (OPO) based on a highly MgO doped periodically poled lithium niobate (PPMgLN) crystal was experimentally demonstrated and the result is presented in this report. The PPMgLN wafer was fabricated from a MgO doped (with 6 mol% doping concentration) lithium niobate crystal by means of high voltage pulse trigged domain reversal technique and has 20 domain reversal periods from 27.8 to with a step of between the neighbor periods. An acousto-optic (AO) Q-switched Nd³⁺:YVO₄ laser was used as the pumping laser. A maximum laser output power of 4.8 W has been achieved for the OPO when the pumping power is 10.8 W and it corresponds to an optic-optic conversion efficiency of 44%. By shifting the PPMgLN wafer, the periods of the domain structure on the PPMgLN wafer can be changed, thus enabling a wide spectral tuning range of the laser output from 1.42 to (for the signal light) and from 2.76 to (for the idler light).