光纤激光器阵列的多抖动法相干合成

 采用自行设计的基于大规模可编程门阵列（FPGA）结构的控制电路,实现了4路光纤激光的多抖动法相干合成。对大气湍流和机械振动引起的相位噪声进行了有效补偿,使远场光斑条纹对比度由开环时的0.21提高到了闭环时的0.93,闭环时远场特定孔径内的能量较开环时提高了3.3倍。该方法还对人为抖动光纤引起的较高频率噪声具有很好的抑制作用,系统闭环后,远场光斑条纹对比度可达到0.72。     

基于偏振自适应和主动相位控制的相干合成的实验研究

进行了非保偏放大器与保偏放大器的相干合成的实验研究。通过随机并行梯度下降（SPGD）算法对非保偏放大器进行偏振自适应控制,使非保偏放大器输出激光的消光比达到11.5 dB,与保偏放大器在同一偏振方向上的光功率占总功率的93.4%。利用单抖动法进行非保偏放大器与保偏放大器的主动相位控制,实现相干合成。实验结果表明:SPGD算法能够有效实现偏振自适应控制,偏振自适应控制前后相干合成远场的条纹对比度从80.1%提高到87.2%,相干合成的效果提升明显;通过增加参与合成的放大器路数,并在各路激光中引入多级功率放大器,能够得到更高的合成功率输出。     

随机并行梯度下降算法模拟两路光纤放大器相干合成与实验研究

对利用随机并行梯度下降(SPGD)算法对多路光纤放大器相干合成进行了数值模拟,并进行了两路瓦级光纤放大器相干合成的实验.实验结果表明,SPGD算法能够有效控制各路光纤激光的相位,系统闭环将目标圆孔内的能量提高了1.57倍;并使得目标圆孔内能量大于理想值80%的概率从27.7%提升到了70.3%.取得了较为明显的相干合成效果.对算法用于多路高功率光纤放大器相干合成的可行性进行了探讨.     

随机并行梯度下降算法用于光纤激光相干合成的理论与实验研究

介绍了随机并行梯度下降(SPGD)算法用于相干合成的基本理论,利用数值模拟的方法对实际相干合成实验中涉及到的算法评价函数、扰动电压分布等参数进行优化选取,确定了实验中应选择的最佳评价函数、扰动电压分布和扰动方式.利用数字信号处理器(DSP)执行SPGD算法,实时控制各路光束的相位,实现了三路瓦量级保偏光纤放大器输出光束的相干合成.实验结果表明,SPGD算法能够有效控制各路光纤激光的相位,系统闭环将合成光束目标圆孔内的能量提高了2.62倍,合成效率达到了理想情形的87%,远场光斑对比度为85%.     

激光器阵列的部分相干性对相干合成远场输出特性的影响

对于相干合成的光纤激光器阵列来说，如何定量的分析阵列的相干性对于评价阵列的性能具有极其重要的意义.文章推导了光纤激光器阵列部分相干合成远场强度分布的解析表达式，详细探讨了激光器阵列的部分相干性对相干合成远场图样分布、中心主瓣宽度、斯特列尔比、桶中功率的影响.最后采用主振荡并联放大器方案对三路掺镱光纤放大器进行实时相位探测与校正，实验给出了三路光纤放大器相干合成的结果. 关键词： 光纤激光器阵列 相干合成 相干度     

模拟退火算法光纤放大器相干合成

提出了利用模拟退火算法实现相干合成的思路。对利用模拟退火算法实现多路光纤放大器相干合成进行了数值模拟,验证了方法的有效性,并分析了算法收敛速度与合成光束数目的关系。进行了两路W量级光纤放大器相干合成的实验,结果表明,模拟退火算法能够有效控制各路光纤激光的相位,系统闭环将目标圆孔内的能量提高了1.8倍,并使得目标圆孔内能量大于理想值80%的概率从19.4%提升到了51.3%,取得了较为明显的相干合成效果。     

激光器阵列的部分相干性对相干合成远场输出特性的影响

对于相干合成的光纤激光器阵列来说，如何定量的分析阵列的相干性对于评价阵列的性能具有极其重要的意义.文章推导了光纤激光器阵列部分相干合成远场强度分布的解析表达式，详细探讨了激光器阵列的部分相干性对相干合成远场图样分布、中心主瓣宽度、斯特列尔比、桶中功率的影响.最后采用主振荡并联放大器方案对三路掺镱光纤放大器进行实时相位探测与校正，实验给出了三路光纤放大器相干合成的结果.     

基于光斑二阶矩的阵列光束倾斜相差自适应控制方法

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。     

三路光纤放大器相干合成技术的实验研究

实验上实现了三路保偏光纤放大器稳定的锁相控制，达到相干合成的输出目的.介绍了实验方案，详细阐述了相位检测与控制的方法并以一路信号光为例给出了相位噪声的测量结果.最后给出了相干合成的远场图样并对其影响因素加以简单分析.实验表明，利用提出的方案增加相干合成的路数是可行的. 关键词： 光纤放大器 相干合成 锁相     

光纤放大器阵列的远场特性研究

从光纤激光器阵列相干合成远场光强分布的解析表达式出发，详细研究了阵列占空比、阵元个数以及阵元的相位误差对相干合成远场图样分布、中心主瓣的角宽度及所占能量的影响. 给出了占空比为12.5%时，三路保偏光纤放大器相干合成的实验结果. 关键词： 光纤激光器阵列 相干合成 相位     

Coherent beam combination of two thulium-doped fiber laser beams with the multi-ditheringtechnique

Coherent beam combination of two thulium-doped fiber laser beams using a multi-dithering technique is presented for the first time. In the experiment, two fiber lasers centered at 1948.6 nm are coherently combined, and a phase modulator based on piezoelectric ceramics transducer is connected in one beam path to compensate for the phase errors between the two beams. When the phase control system is closed loop, the fringe contrast of the far-field intensity pattern is improved to be more than 75%, from 15% in open-loop, and the residual phase error is less than λ/20. The experimental results show that the performance of the phase control system is robust and the control bandwidth is more than 1 kHz, which indicates that the above approach can be scaled to facilitate the coherent beam combination of kilo-watt level thulium-doped fiberlaser.     

A coherent beam combination system based on double PZT phase modulators

A novel coherent beam combination system based on double piezoelectric ceramics transducer (PZT) phase modulators is presented and demonstrated for the first time. In this system, two different PZT phase modulators are used for high frequency phase modulation and low frequency phase control, respectively, while in previous demonstrated system, LiNbO₃ phase modulators are often employed. The inherent low insert loss and high laser-induced damage threshold of the PZT phase modulator makes the new proposed system more compact and stable. By the way, the experiment of coherent beam combination of two 5-W fiber laser beams based on double PZT phase modulators is done. In the experiment, the PZT phase modulator with 500-kHz frequency response point made in home is used for high frequency phase modulating and another one with 0～30-kHz linear frequency response range for phase controlling. When the phase control system is in the closed loop, the fringe contrast of far-field intensity pattern is improved to be more than 90 % from 5 % in open loop.     

Coherent beam combining of fiber amplifier based on adaptive polarization and active phase control

Coherent beam combining (CBC) of a polarization-maintaining fiber amplifier and a non-polarization-maintaining fiber amplifier is presented. The experiment is based on adaptive polarization control and active phase control. The stochastic parallel gradient decent (SPGD) algorithm is used for the adaptive polarization control in the non-polarization-maintaining fiber amplifier and the active phase control is realized by single frequency dithering (SFD) algorithm. When the adaptive polarization control system and the phase control system go into closed loop, the fringe contrast of far-field intensity pattern is improved to more than 87.7%. A scalable architecture for CBC of two styles fiber amplifiers is also proposed.     

Coherent combination of two ytterbium fiber amplifier based on an active segmented mirror

To control the phase noise of two ytterbium fiber amplifiers, a coherent combination system based on an active segmented mirror (ASM) has been established in our laboratory. The ASM is controlled by a feed back control loop on the basis of a Peak Rate (PR) algorithm which is realized on a DSP + FPGA hardware control board. Experimental results indicate that when the control loop is off, the far-field interference pattern is blurred and dynamic, while when it is on, the far-field beams interference pattern achieves clear and stable. At two different output powers, the contrasts of the interference stripes are improved from 7% to 19% and 8% to 28% respectively.     

Tiled-aperture coherent beam combining of two high-power fibre amplifiers

We demonstrate coherent beam combining of two tiled-aperture single-frequency fibre amplifiers with a total output power of 29.65 W by using the multi-dithering technique. The two laser beams are packaged closely by using free-space mirrors side by side into a tiled-aperture with a near-field fill factor of 62%. Active phase control of the amplifier is performed on commercially available digital lock-in amplifiers. Experimental results show that the power contained in the main-lobe in closed-loop is 1.72 times greater than that in open-loop, which is 86% for the ideal case. The fringe contrast of the far-field fringe pattern is as high as 80% when the system is in closed-loop. The beam quality of the combined beam is computed to be BQ = 1.48. The whole system in closed-loop performs well in a long-time observation.     

基于体布拉格光栅的光谱合成的数值分析

 建立了分别用一个和两个反射式体布拉格光栅实现两路和三路光束合成的物理模型，模型中考虑了体布拉格光栅的吸收，并假设入射光束的光谱具有高斯线型。通过对两路和三路光谱合成的数值分析可知:当光谱宽度为0.1 nm时，两路和三路光谱合成的效率分别为98.76%和97.69%;当光谱宽度为0.3 nm的时候，对应的效率分别为97.34%和95.78%。随着光谱宽度的增加，合成的效率明显降低。当光谱宽度较窄时，实现多路光束较高的合成效率是可行的，这为高能激光的获得提供了一种确实可行的方法。     

Active coherent beam combination of two high-power single-frequency nanosecond fiber amplifiers

We report on active coherent beam combining of two single-frequency nanosecond fiber amplifiers by using stochastic parallel gradient descent algorithm. Each fiber amplifier produces an average power of more than 100 W by using three-stage cascaded amplification. The two laser beams are actively phase-locked with a total average power of 215.8 W, producing ~8 ns pulses at 10 MHz repetition rate. The contrast of the far-field intensity pattern of the coherently combined beam is more than 83%.     

Coherent beam combination of 1.08 kW fiber amplifier array using single frequency dithering technique

Coherent beam combination of a 1.08?kW fiber amplifier array has been demonstrated for the first time, to our knowledge. In the experiment, nine fiber amplifiers are tiled into a 3×3 array, and the output power of each amplifier is approximately 120?W. A single frequency dithering algorithm is used to compensate the phase noises between the elements, which runs on a signal processor based on field programmable gate array for phase control on the fiber amplifiers. When the phase control system goes into closed loop, the fringe contrast of the far-field intensity pattern is improved to more than 85%, and the residual phase error is less than λ/15.