Propagation properties of high-power fiber laser with high-order-mode(HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by...Propagation properties of high-power fiber laser with high-order-mode(HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by the power in the bucket(PIB) metric. It is shown that PIB is mainly dependent on HOM content rather than the relative phase between the fundamental mode and HOM. The PIB in vacuum is more than 80% when the power fraction of the HOM is controlled to be less than 50% at 5 km. The relative phase has an impact on the peak intensity position and concentration of the far-field intensity distribution. If an adaptive optics system is used to correct the peak intensity deviation, the results indicate that there exists a maximal value of PIB as relative phase increases. Such effect is weakened when propagating in turbulence. Compared to the laser beams without HOM, laser beams with HOM content are less influenced by the turbulence and can reduce average intensity fluctuation. The results may be useful in the design of a high-power fiber laser system.展开更多
激光光束的指向噪声对物理量的精密测量、激光材料加工、自由空间远距离光通讯、星载激光对准系统等许多应用场景都有负面影响,抑制光束指向噪声的研究有着重要意义。本文在实验上利用Sagnac干涉仪针对压电陶瓷产生的倾斜指向噪声抑制...激光光束的指向噪声对物理量的精密测量、激光材料加工、自由空间远距离光通讯、星载激光对准系统等许多应用场景都有负面影响,抑制光束指向噪声的研究有着重要意义。本文在实验上利用Sagnac干涉仪针对压电陶瓷产生的倾斜指向噪声抑制开展了研究,系统通过高阶模式滤波原理将指向噪声激发的厄米-高斯光模分离。理论上使用传输矩阵进行分析,给出了干涉仪抑制指向噪声的原理及与相关参数的关系。实验上搭建Sagnac干涉仪,对装有反射镜压电陶瓷产生的指向噪声进行抑制,并与压电陶瓷随驱动电压相同的指向噪声直接探测的情况进行了相应的对比。实验结果表明,当压电倾斜镜产生2.5μrad的信号时,干涉仪能抑制43.3 d B的指向噪声。该方法不需要闭环反馈技术,适用于连续波激光系统中,尤其是需要快速修正的场景。展开更多
分析了一种复合式高速直升机的飞行原理,设计了不同飞行模式下的操纵策略,并建立了飞行动力学模型。考虑传感器噪声和复杂飞行环境导致的系统状态难以准确测量的问题,提出了一种基于高阶滑模微分器的姿态自抗扰控制算法。在MATLAB/Simul...分析了一种复合式高速直升机的飞行原理,设计了不同飞行模式下的操纵策略,并建立了飞行动力学模型。考虑传感器噪声和复杂飞行环境导致的系统状态难以准确测量的问题,提出了一种基于高阶滑模微分器的姿态自抗扰控制算法。在MATLAB/Simulink环境下构建了复合式高速直升机姿态控制系统,并与PID(proportion integral differential)控制器和LQG(linear quadratic Gaussian)控制器进行了仿真对比。研究结果表明:所提出的基于高阶滑模微分器的姿态自抗扰控制器能够实现对姿态角的无超调跟踪,相较于PID控制器和LQG控制器,误差收敛速度分别提升31.5%和64.2%,且在噪声干扰下,最大跟踪误差比LQG控制器小34.2%,比PID控制器小39.5%。展开更多
基金sponsored by the Innovation Foundation for Excellent Graduates in the National University of Defense Technology under grant no. B120704the Open Research Fund of Key Laboratory of Atmospheric Composition and Optical Radiation under grant no.2012JJ05
文摘Propagation properties of high-power fiber laser with high-order-mode(HOM) content are studied numerically for the first time to the best of our knowledge. The effect of HOM on the propagation property is evaluated by the power in the bucket(PIB) metric. It is shown that PIB is mainly dependent on HOM content rather than the relative phase between the fundamental mode and HOM. The PIB in vacuum is more than 80% when the power fraction of the HOM is controlled to be less than 50% at 5 km. The relative phase has an impact on the peak intensity position and concentration of the far-field intensity distribution. If an adaptive optics system is used to correct the peak intensity deviation, the results indicate that there exists a maximal value of PIB as relative phase increases. Such effect is weakened when propagating in turbulence. Compared to the laser beams without HOM, laser beams with HOM content are less influenced by the turbulence and can reduce average intensity fluctuation. The results may be useful in the design of a high-power fiber laser system.
文摘激光光束的指向噪声对物理量的精密测量、激光材料加工、自由空间远距离光通讯、星载激光对准系统等许多应用场景都有负面影响,抑制光束指向噪声的研究有着重要意义。本文在实验上利用Sagnac干涉仪针对压电陶瓷产生的倾斜指向噪声抑制开展了研究,系统通过高阶模式滤波原理将指向噪声激发的厄米-高斯光模分离。理论上使用传输矩阵进行分析,给出了干涉仪抑制指向噪声的原理及与相关参数的关系。实验上搭建Sagnac干涉仪,对装有反射镜压电陶瓷产生的指向噪声进行抑制,并与压电陶瓷随驱动电压相同的指向噪声直接探测的情况进行了相应的对比。实验结果表明,当压电倾斜镜产生2.5μrad的信号时,干涉仪能抑制43.3 d B的指向噪声。该方法不需要闭环反馈技术,适用于连续波激光系统中,尤其是需要快速修正的场景。
文摘针对高速列车速度跟踪控制过程中系统易受内外部扰动的影响,导致控制精度低的问题,设计一种基于分数阶积分滑模的高速列车速度跟踪自抗扰控制(Active Disturbance Rejection Control,ADRC)方案.该方案对ADRC中的线性扩张状态观测器(Linear Extended State Observer,LESO)和非线性误差反馈控制律分别进行改进.首先,在LESO设计中,引入总扰动微分状态变量,提高观测器扰动观测能力;其次,采用分数阶积分滑模控制(Fractional Order Integral Sliding Mode Control,FOISMC)改进非线性误差反馈控制律,削弱滑模控制抖振的同时提高系统跟踪精度;最后,设计复合分数阶积分滑模自抗扰控制方案,以CRH3型列车参数进行期望速度曲线仿真跟踪,验证控制方案的跟踪性能,并将该控制方案与其他传统控制方案进行比较分析.研究结果表明:在相同条件和相同外加扰动作用下,所提控制方案较其他控制方案跟踪精度更高,抗干扰能力更强,速度追踪最大误差为0.00005 m/s.
文摘分析了一种复合式高速直升机的飞行原理,设计了不同飞行模式下的操纵策略,并建立了飞行动力学模型。考虑传感器噪声和复杂飞行环境导致的系统状态难以准确测量的问题,提出了一种基于高阶滑模微分器的姿态自抗扰控制算法。在MATLAB/Simulink环境下构建了复合式高速直升机姿态控制系统,并与PID(proportion integral differential)控制器和LQG(linear quadratic Gaussian)控制器进行了仿真对比。研究结果表明:所提出的基于高阶滑模微分器的姿态自抗扰控制器能够实现对姿态角的无超调跟踪,相较于PID控制器和LQG控制器,误差收敛速度分别提升31.5%和64.2%,且在噪声干扰下,最大跟踪误差比LQG控制器小34.2%,比PID控制器小39.5%。
