三路掺镱光纤放大器的相干合成实验研究

Coherent beam combination of three ytterbium fiber amplifiers

光纤激光相干合成技术是实现高功率、高亮度光纤激光系统的重要技术途径。采用主振荡并联放大器(MOPA)方案对三路掺镱光纤放大器进行实时相位探测与校正,其中每路光纤放大器的输出功率大于等于1 W,三路总功率大于等于3 W。采用铌酸锂光纤相位调制器,外差法系统的移频量为40 MHz,相位探测与校正精度优于λ/20,整个光路为全保偏光路。实验分别给出了两路和三路光纤放大器的相干合成结果。系统开环时,远场光斑为动态、模糊干涉条纹,条纹可见度为7%和6%;系统闭环运行时,远场光斑为稳定、高对比度干涉条纹,条纹可见度有大幅度提高,达到44%和48%。这表明闭环控制使两路和三路光纤激光的相位变化得到了有效补偿,系统实现了相位锁定运行和高相干度合成输出。

Coherent beam combination of fiber laser array is an important technology in realizing high power fiber laser system. In this paper, master oscillator-power amplifier scheme is used to realize phase control of three ytterbium fiber amplifiers. In the experiments, the output power of each ytterbium fiber amplifier is not less than 1 W and the total output power of the three amplifiers is not less than 3 W. Phases are controlled by LiNbO, phase modulator. The heterodyne detection control system works at 40 MHz and the control precision is λ/20. The fibers are polarizedly maintained. The experimental results of both two and three fiber amplifiers are given. When the control loop is off, the far field interference pattern is dynamic and blurred. While the control loop is on, the far field interference pattern turns to stable and clear. In both feed back control loops, the phase noises of fiber amplifier array are properly controlled and coherent beam combination is aehieved. The results lay a foundation to achieve coherent beam combination of fiber laser array and the number of amplifiers may be increased.