小芯径硫系玻璃光纤的制备及其非线性光学应用

通过动态蒸馏提纯技术制备了高纯Ge-As-Se和Ge-As-S硫系玻璃。采用两步棒管法拉制了以Ge-As-Se玻璃为纤芯、Ge-As-S玻璃为包层的小芯径阶跃折射率光纤, 并使用飞秒激光抽运光纤测试了超连续谱的产生。以Al 和GaCl₃分别作为除氧剂和C/H纯化剂可以有效消除玻璃中的C、H和O杂质。制备的GeAsSe/GeAsS光纤在2~9 μm波段表现出优异的传输性能, 光纤数值孔径约为1.3; 采用重复频率为10.5 MHz、脉冲宽度为320 fs、中心波长为4.0 μm、峰值功率为4.6 kW激光抽运长度为22 cm、芯径为6 μm的光纤, 获得了覆盖1.9~8.2 μm、光谱平坦度为±10 dB、平均功率为4.5 mW的超连续谱。     

低损耗As-S玻璃光纤的制备与应用研究

采用反复蒸馏提纯技术和开放式动态蒸馏相结合的工艺, 制备了高纯As-S玻璃, 基本消除了玻璃在2.9、4和6.3 μm处的杂质吸收。利用旋转法制备出壁厚均匀、表面质量优异的硫系玻璃套管。采用棒管法拉制出丝径50 μm, 芯径40 μm具有芯包结构的硫系玻璃光纤。拉制的As-S光纤机械性能和光学性能优异, 光纤丝径波动小于1%, 弯曲半径优于4 mm, 中红外波段损耗基线小于0.5 dB/m。制备出像元呈正方形排列, 出端规格64×9, 入端规格192×3, 用于线-面转换的红外传像束, 像束断丝率为2.7%。利用该异型传像束成功实现了长线阵的红外推扫成像。     

碲化镉片上集成波导的自相位调制特性研究

中红外(2.5μm～25μm)波段包含许多重要的原子和分子共振峰，因此中红外超连续谱广泛应用于生物医学、光谱学和环境科学等领域。碲化镉(cadmium telluride, CdTe)在中红外波段具有超宽的透射光谱范围0.86μm～25μm，同时CdTe具有较大的三阶非线性系数，是实现中红外超连续谱的理想材料。本文设计并加工了一种基于CdTe为芯层、低折射率介质硫化镉为缓冲层、硅为衬底的波导。采用广义非线性薛定谔方程仿真了该波导以中心波长为5.5μm中红外激光作为泵浦，能够实现4.1μm～9.7μm的超连续谱输出。实验中通过湿法刻蚀制作CdTe多晶波导，并采用中心波长为1030 nm，脉冲宽度为250 fs的激光器作为泵浦源，观察到在波导中发生明显的自相位调制而产生的光谱展宽。该工作为CdTe集成波导应用于中红外超连续谱及中红外波段的片上光学器件提供了新的可能。     

多模光纤作可饱和吸收体的锁模光纤激光器

本文报道了一种新兴的锁模方式-多模干涉锁模。这种锁模方式结构简单,搭建方便。在单模光纤激光器中熔接二段短的渐变折射率多模光纤,利用这种单模-多模-单模(SMS)结构的模式干涉效应实现可饱和吸收机制,从而实现锁模脉冲输出。SMS结构实现锁模需要对多模光纤的长度进行精确控制,本文提出将SMS结构缠绕进偏振控制器中,通过理论推导偏振控制器对多模光纤中传输光相位的调控,以实现可饱和吸收效应。在263 mW泵浦功率下实现了24.83 MHz重复频率的传统孤子脉冲输出,其脉冲间隔为40.12 ns,信噪比为50.8 dB,中心波长为1881.7 nm。通过调节偏振控制器和泵浦功率实现孤子分子与传统孤子脉冲的转换。在410 mW的泵浦阈值下实现了25 MHz重复频率的孤子分子脉冲输出,其脉冲间隔为40.3 ns,信噪比为54.4 dB,中心波长为1887.60 nm。     

光孤子通信系统的色散控制研究

光纤色散特性是支撑光纤孤子通信的决定性因素。比较了目前的几种色散补偿方案后,着重对相位共轭控制的色散控制方式进行了分析研究,该方式利用光纤非线性四波混频产生与输入光脉冲信号相位共轭的输出光脉冲信号,光脉冲的频谱以泵浦光频为中心进行反转,构建成相位共轭器,实现了对放大自发辐射(ASE)噪声、孤子相互作用与色散波等的控制,达到提高系统传输速率、距离和通信容量的目的。     

高功率双包层Er3+/Yb3+共掺光纤放大器的动态响应

基于速率方程的离散算法,分析了双包层Er3 /Yb3 共掺光纤放大器的动态响应,显示了输出功率和增益的动态特征。当单个脉冲注入放大器时,输出脉冲的峰值功率不仅依赖于输入脉冲的峰值功率,而且依赖于泵浦功率;当脉冲序列注入时,输出脉冲的功率和增益最终将收敛于它们的稳态值。在双信道情况下,输入脉冲重叠时的输出功率和增益变得更陡峭。在连续波泵浦下,反向自发辐射输出功率(ASE-)首先快速地增加到峰值功率,然后单调下降到稳态值;在脉冲波泵浦下,反向自发辐射输出功率(ASE )与光纤长度成反比,而ASE-与光纤长度成正比。     

高功率掺镱双包层光纤激光器的优化和设计

针对高功率掺杂光纤激光器设计中存在的多个设计参数无法全局最优化的问题,本文提出一种高效灵活的遗传算法对高功率掺镱双包层光纤激光器的六个重要参数（泵浦波长、信号波长、谐振腔的反射率、光纤长度、掺杂浓度、泵浦功率）同时进行多维变量优化。该方法采用一种全局优化算法（遗传算法1,分别讨论了在输出信号功率作为遗传算法中的目标函数时,高功率掺镱双包层光纤激光器的各个系统参数配置。实验结果表明,在所设定的波长范围内,最优的泵浦波长和信号波长分别为975nm和1044nm;最优光纤长度和掺杂浓度有一一对应的取值;谐振腔输入镜面反射率应越大越好,而输出镜面反射率与泵浦功率的大小相关。     

不同晶相MnS制备及光解H2S制氢性能研究

采用溶剂热法成功制备了具有立方结构的α-MnS和六方结构的γ-MnS。通过X射线衍射(XRD), 扫描电子显微镜(SEM), 透射电子显微镜(TEM)、高分辨透射电镜(HRTEM)、选区电子衍射(SAED)和紫外-可见吸收光谱(UV-Vis), 对样品的物相组成、显微形貌、光学性质进行了研究, 并对不同晶相MnS在可见光(λ > 420 nm)和全光谱下光解H₂S制氢性能进行了研究。结果表明: α, γ-MnS在可见光下都具有光解H₂S制氢活性, 且相比于热力学稳定相的α-MnS (4.24 μmol/(g·h)), 亚稳态的γ-MnS (23.38 μmol/(g·h))具有更好的催化性能。相对于可见光, α, γ-MnS在全光谱下的产氢速率明显提高, 其中γ-MnS在全光谱下具有最大的光解H₂S制氢活性, 其产氢速率可达 2272.69 μmol/(g·h)。值得注意的是, 在6 h的光催化测试过程中, α, γ-MnS都展示较好的抗光腐蚀能力和光催化稳定性。此外, 对α, γ-MnS光催化分解H₂S制氢机理进行了分析, 通过对α, γ-MnS光电化学性质的研究, 对其光催化活性存在差异的原因进行了探讨。     

纤维厚度和体积分数对压电纤维复合物应变性能的影响

实验制备了不同纤维厚度和体积分数的压电纤维复合物, 并在0.1 Hz的激励电压下测试了压电纤维复合物的自由应变性能和驱动性能, 研究复合物典型结构参数对其性能的影响。实验发现, 随着压电纤维厚度增加, 复合物自由应变和顶端位移下降, 1000 V激励电压下, 纤维厚度为200 μm样品纵向自由应变为665 με, 驱动Mylar膜产生的顶端位移为1.9 mm, 而纤维厚度为300 μm和400 μm样品的纵向自由应变仅为纤维厚度为200 μm样品的23.2%和11.7%, 顶端位移为纤维厚度为200 μm样品的45.8%和19.0%。压电纤维复合物具有驱动正交异性, 横向自由应变、纵向自由应变以及横向效应系数随着纤维体积分数的降低而减小, 纤维体积分数为74%的复合物其横向自由应变和纵向自由应变分别为体积分数为59%样品的2.04倍和1.72倍, 横向效应系数也从0.519减小到0.451。     

亚纳秒脉冲泵浦机制超短脉冲和超连续谱的产生

本文仿真研究了亚纳秒脉冲泵浦机制超短脉冲的产生和超连续谱的形成。首先,简要介绍了激光在非线性介质传输所满足的广义非线性薛定谔方程;然后,研究了分步傅里叶法时域步长的选取和空间步长高精度自适应变化的实现;最后,逐渐增加入射脉冲的峰值功率,仿真了超连续谱的形成。结果表明:亚皮秒量级的超短脉冲可以由亚纳秒脉冲经过调制不稳定性分裂产生,而与超短脉冲有关的高阶非线性效应(包括自陡效应、脉冲内拉曼散射效应、高阶孤子分解)最终导致了30 dB带宽从481 nm一直延伸到1 750 nm超连续谱的形成。     

Suspended core tellurite glass optical fibers for infrared supercontinuum generation

We report the fabrication and characterization of tellurite TeO₂-ZnO-Na₂O (TZN) microstructured suspended core optical fibers (MOFs). These fibers are designed for infrared supercontinuum generation with zero dispersion wavelength (ZDW) at 1.45 μm. The measured losses at this wavelength are approximately 6 dB/m for a MOF with a 2.2 μm diameter core. The effective area of a particular fiber is 3.5 μm² and the nonlinear coefficient is calculated to be 437 W⁻¹km⁻¹. By pumping a 20 cm long fiber at 1.56 μm with a sub-nJ femtosecond laser source, we generate a supercontinuum (SC) spanning over 800 nm in the 1-2 μm wavelength range.     

Concentration effects on the IR-luminescent channels for Er- and Ho-doped LiYF4 crystals

In this paper we report the ideal concentrations for the main infrared laseof channels r the Er³⁺- and Ho³⁺-doped LiYF₄ (YLF) crystals, under Xe lamp pumping. The number of photons per luminescent channel was also obtained for both ions. It was determined that 10–20% of Erbium at.wt is the ideal concentration for laser action at 2.74 μm, as well as the 1.7% Er-doped YLF crystal is the best one for lasing at 0.85, 1.23, and 1.72 μm under flashlamp pumping. The present method is a good approach in order to indicate the ideal concentration for an optimized four-level laser system. For the transitions at 1.62 μm (Er:YLF) and at 2.07 μm (Ho:YLF) it was observed that the luminescence intensities are maximized in the concentration range (25–35)% for Er ions and in the range (10–15)% for Ho ions in the YLF crystals. However, these concentration values are much higher than the ones used in a practical three-level laser system.     

Bismuth activated alumosilicate optical fibers fabricated by surface-plasma chemical vapor deposition technology

Plasma chemical technology is experimentally applied to the fabrication of a Bi-activated alumosilicate-core pure-silica-cladding fiber preform. To the best of our knowledge, this is the first time this technology has been applied in this way. We measure gain efficiency at pumping by a 1058 nm wavelength Yb fiber laser in a piece of a newly obtained fiber 20 m in length within 100-1200 nm wavelengths band. The gain efficiency reaches as high as 0.2 dB/mW. Bi-activated alumosilicate-core pure-silica-cladding fiber that is not more than 12 m in length serves a basis for a 1 W output power fiber laser emitting at the wavelength of 1160 nm with 8% slope efficiency. We also measure the photoluminescence spectrum and kinetics of Bi centers responsible for laser emission under the excitation of 193 nm wavelength ArF laser pulses.     

熔融纺丝过程优化制备细直径碳化硅纤维及其对力学性能的影响

强度、模量和柔顺性作为碳化硅(SiC)纤维重要的力学性能受到纤维直径大小的影响, 而制备工艺中的熔融纺丝过程对纤维直径起决定作用。本工作研究了纺丝温度、纺丝压力和卷绕速度对聚碳硅烷(Polycarbosilane, PCS)原纤维直径的影响, 分析了纺丝过程中纤维断裂的原因, 并初步探究了SiC纤维直径与力学性能的关系。结果表明, 在一定范围内降低纺丝温度、降低纺丝压力和提高卷绕速度均能显著减小原纤维的直径。在连续纺丝的前提下, 最优纺丝工艺下得到的PCS原纤维直径为13.5 μm。随着PCS纤维直径由18.3 μm减小至13.5 μm, SiC纤维直径则由13.8 μm减小至9.5 μm, 而SiC纤维的强度与模量分别由1.7、181 GPa提高至2.9、233 GPa, 强度分布更为集中, 柔顺性得到显著提高。     

Optical power flow in plastic-clad silica fibers

Using the time-independent power-flow equation, we have examined the mode coupling caused by intrinsic perturbation effects of step-index plastic clad silica fiber carrying more than 10(5) modes. Result show that the equilibrium mode distribution for this fiber is achieved at a length of approximate 550 m, which is longer than reported previously. While this coupling length is much longer than that of plastic optical fibers, it is sorter than that of all-glass fibers.     

Ultrabroad supercontinuum generation in tellurite equiangular spiral photonic crystal fiber

Simulations are presented of a very broad and flat supercontinuum (SC) in both the normal and anomalous group velocity dispersion regimes of the same equiangular spiral photonic crystal fiber at low pumping powers. For a pump wavelength at 1557?nm and average pump power of 11.2?mW, we obtained a bandwidth >3?μm (970?nm–4100?nm) at 40 dB below the peak spectral power with fiber dispersion ～2.1?ps/km nm at 1557?nm. In the same fiber, at pump wavelength 1930?nm and average pump power of 12?mW the SC bandwidth was more than two octaves (1300?nm–3700?nm) and dispersion was ～1.3?ps/km nm at 1930?nm. This demonstrates the potential use of the fiber for multi-wavelength pumping with commercially available sources at fairly low power.     

Passively Q-switched Tm(3+)-doped silica fiber lasers

By splicing on a length of Ho(3+)-doped silica fiber onto a diode-pumped double-clad Tm(3+)-doped silica fiber, stable passive Q switching of the Tm(3+)-doped silica fiber laser is demonstrated. The formation of Q-switched pulses was found to depend on both the length and the position of the Ho(3+)-doped silica fiber that was inserted into the fiber laser cavity. For stable Q-switched pulse generation, Ho(3+)-doped silica fiber lengths shorter than twice the absorption depth must be used. For long Ho(3+)-doped silica fiber lengths, randomly generated pulses are observed at operating wavelengths longer than 2090 nm, which are attributed to intracavity pumping of the Ho(3+)-doped silica fiber.