Self-adaptiue tilt control method based on second order moment of beam for laser array
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摘要: 针对阵列光束相干合成中存在的倾斜相差大的问题，提出了基于合成光束远场光斑二阶矩的阵列光束倾斜相差自适应控制方法。以合成光束远场光斑二阶矩作为评价函数，理论上模拟了采用随机并行梯度下降算法实现7路光束的倾斜闭环控制过程。实验上搭建了7路光纤激光相干合成系统，利用自适应光纤准直器对倾斜相差进行校正。以合成光束远场光斑的二阶矩作为评价函数，采用随机并行梯度下降算法，实现了7路光束的倾斜的闭环控制，合成光束模拟远场光斑的桶中功率由0.05 V提升至1.95 V。实验中将倾斜扰动的增益系数变为与二阶矩相关的函数，实现了自适应变增益系数的倾斜闭环，在一定程度上提升了倾斜控制的带宽。从理论上和实验上验证了基于光斑二阶矩的倾斜相差自适应控制方法在光束合成及合成孔径探测领域应用的可行性。
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关键词:
- 相干合成 /
- 倾斜控制 /
- 光斑二阶矩 /
- 阵列光束 /
- 随机并行梯度下降算法.
Abstract: Aiming at the problem of tilt control in coherent beam combining of laser array, a tilt control method, of which the evaluation function is based on second order moment of combined laser beam, is proposed. The performances of the tilt control method are investigated theoretically and experimentally. In the theoretical study, adopting the second order moment of the combined beam as the evaluation function, the tilt control process of 7 laser beam is simulated based on stochastic parallel gradient descent algorithm. In the experiments, a coherent beam combining system of 7-channel fiber array is built and an adaptive fiber collimator is used as the tilt-control device. Adopting the stochastic parallel gradient descent algorithm, the closed-loop operation of tilt control is achieved with the second order moment of the combined spot as the evaluation function. The theoretical and experimental results show that the tilt control method based on the second order moment of laser beam has great potential on coherent beam combination. -
图 1 不同倾斜相差下，阵列光束相干合成远场光斑分布
Figure 1. Far-field spot distribution of coherent beam under different tilt phase error
图 3 倾斜闭环过程中光斑二阶矩的变化
Figure 3. Variation of second order moment of spot in tilt control process
图 4 7路光纤激光相干合成系统
Figure 4. Coherent beam combining system of 7-channel fiber laser array
图 6 倾斜闭环过程中光斑二阶矩的变化
Figure 6. Variation of second order moment of spot in tilt closed-loop
图 7 相位、倾斜闭环过程中，PD内桶中功率的变化情况
Figure 7. Variation of power in the bucket in phase and tilt control process
图 8 不同变增益下，光斑二阶矩的变化情况
Figure 8. Variation of second order moment of spot under different gain parameter
表 1 不同倾斜相差对应的光斑二阶矩
Table 1. Second order moment of coherent beam under different tilt phase error
tilt phase error (RMS)/ μrad σx/cm σy/cm 0 0.73 0.73 10 0.83 1.04 20 1.60 1.52 30 1.51 2.58 
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