为了解决四旋翼飞行器轨迹跟踪中状态量收敛速度慢、易发散等问题, 提出了一种双环混合有限时间控制策略。根据Newton-Euler方程推导出四旋翼的动力学模型, 再根据时间尺度原理将其分为内外两个控制环。外环采用有限时间控制策略来加快三轴位置量与偏航角的收敛速度; 内环采用快速非奇异终端滑模控制技术来实现姿态角的快速收敛。搭建了四旋翼的虚拟样机, 在三维仿真环境下模拟其轨迹跟踪控制效果。由仿真结果可知: 与其他两种常见的控制器相比, 所设计的控制器的控制精度、鲁棒性以及跟踪效果均最好, 并且能较好地满足四旋翼轨迹跟踪控制的需求。

提出了利用单目视觉与激光测距仪混合的航天器间相对位置和姿态参数测量的解析算法。首先利用四元数测量算法，采用5个非共面特征光点和单目视觉获取航天器间相对位置和姿态参数的解析解，并对解析解进行修正；然后，将上述6D位姿参数与激光测距仪获取的1D距离进行融合，以进一步对6D位姿参数进行修正。最后，通过计算实例对该算法进行数学仿真，仿真结果表明：该算法保证了在相机标定和特征光点提取及匹配较大误差下的位姿参数的估计精度，能够满足航天器相对位姿确定精度和实时计算要求。

从实验上研究了掺镱(Yb)双包层光纤放大器中单频脉冲信号放大时,受激布里渊散射(SBS)引起的脉冲畸变现象。实验中采用的单频双包层光纤放大器光纤长度14 m,内包层直径130 μm,纤芯模场直径6.5 μm,在单频脉宽200 ns脉冲放大,且峰值功率3.3 W时观察到后向SBS脉冲,脉宽明显小于输入信号脉宽,分析了受激布里渊散射引起放大脉冲波形畸变的随机特性和功率特性,并采用自由光谱范围30 GHz的法布里-珀罗(F-P)扫描干涉仪验证了SBS频移。

By employing a simple model of describing three-level lasers, we have theoretically investigated the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers. And based on the theoretical analysis we have proposed a promising method to suppress self-pulsing behaviour in the fibre lasers.

提出并实验证实了一种刻写光栅时既能保护相位版又能对光栅的反射波长进行微调的方法.通过调整光纤和相位版之间的距离,利用1 550 nm单模光纤和掺铒分别实现了0.48 nm和2.2 nm的光栅反射波长的调节.在相位版和光纤之间的距离保持在3 mm的条件下,既可以保护相位版又可以获得高质量的光栅.

Based on the rate equation, the amplification performance of small-mode-area (SMA) and large-mode-area (LMA) ytterbium-doped double-clad fiber amplifiers was studied using the finite-difference method. The Yb-doped double-clad fibers with the mode diameter 6.5 μm and 20 μm were used as the gain media for the amplification of narrow-band signals. Under the pump laser at the center wavelength of 915 nm, the relationships between output power and input signal power, pump power as well as fiber length, were discussed for SMA and LMA. Especially for LMA fiber amplifiers, it is important to choose the optimal fiber length. For the fiber amplifier with different mode diameters, the optimal pump power and fiber length were also analyzed. It is obtained that the critical pump power is about 4 W with the fiber length of 4 m, which is in accord with the experimental results. The results provide a theoretical guide to optimize fiber type and fiber length considering available signal and pump power, desired gain and mode requirement of fiber amplifiers.

By solving a set of time-dependent equations, the characteristics of the ytterbium-doped double-clad fiber amplifier are presented. Besides the steady state in the fiber of the upper-state population, pump power and amplified spontaneous emission without the input signal, the dynamic characteristics of the high power Gaussian pulse amplification like the evolution of pulse waveform distortion, upper-state population distribution and stored energy and pulse energy of the amplifier under the forward and backward pump, are simulated. The relations between the output pulse energy of the amplifier and the different input pulse peak power or pump power are also discussed. The models and results can provide important guide for the design and optimization of the high power pulse amplification.

A diode-pumped Yb-doped double-clad fiber amplifier (YDDCFA) with the narrow bandwidth continuous wave (CW) and pulse input signal is investigated. The input single-mode (SM) signal bandwidth is 10^(-4) nm from a distributed feedback (DFB) fiber laser. The saturated gain of the CW amplification is 11 dB at the forward pump. And besides CW signals, we also amplify pulses with duration of 150 ns and the 1-Hz repetition. The pulse is amplified to 2 W of peak power, 0.31 microjoule of energy, 23 dB of gain and less than 6% of stability at the forward pump power of 1.4 W. For higher power, reflections and backscattering can generate the self pulsation in the amplifier. The results are important for the development of the narrow-band double-clad fiber amplifier.

Yb-doped phase-shifted fiber Bragg grating (PS-FBG) has been fabricated with phase shift introduced by shielded method. In the fabrication process, the PS-FBG is used as the laser cavity. Whether the introduced phase-shift is π/2 or not is determined by the laser output power. As long as the output power of the laser begins to drop down, the exposure is stopped, and the phase shift is π/2 then. It is necessary to anneal the PS-FBG to stabilize its characteristics, which will reduce the introduced phase-shift. The second exposure of the PS-FBG is needed to restore the π/2 phase shift. A fiber grating laser has been made with the method. When the pump power is 100 mW, the laser output is 25 mW with signal-noise-ratio (SNR) of 60 dB. Within 1 h the output fluctuation of the laser is less than 1%. The laser is always under single-mode operation when the temperature of the fiber grating is tuned between 25 ℃ and 30 ℃.

采用遮挡法引入相移制作了掺Yb相移光纤光栅(PS-FBG)。在制作光栅的过程中,将其作为激光器的谐振腔,通过监测激光器的输出功率来确定相移大小。当激光器的输出功率开始下降时,停止曝光,此时引入的相移为π/2。为了使光栅的特性尽快稳定下来需要对光栅进行退火,这将导致引入的相移小于π/2。为了弥补退火过程中引起的相移降低,需要对退火后的光栅进行二次曝光,以使光栅的相移恢复π/2。利用该方法制作了一只光纤光栅激光器。当抽运功率为100 mW时,获得了25 mW的输出功率,信噪比(SNR)为60 dB。在1 h内,输出功率波动小于1%。当光栅的温度在25～30 ℃之间变化时,激光器单纵模运转。