复合调制掺Yb^(3+)兆瓦级光纤激光系统

Multi-Modulation Yb^(3+)Doped Megawatt Fiber Laser System

提出了一种主振荡光纤放大系统,围绕提高脉冲信号的峰值功率和拓宽系统重复频率的调制范围两方面进行了实验研究。实验采用电脉冲调制和声光调制的方式对光脉冲序列进行调制,抑制了半导体种子源在小信号放大时产生的放大自发辐射效应和自激振荡,解除了种子源对系统重复频率的限制,使系统的重复频率在1~200kHz范围内连续可调。在声光调制器对光脉冲的调制过程中,声光Q开关有效抑制了放大过程中由自相位调制引起的光谱展宽。实验采用大模场棒状光子晶体光纤作为增益介质,提高了光脉冲的峰值功率和输出光的光束质量,抑制了因峰值功率过高引起的非线性效应,最终实现了脉冲宽度为1.12ns、峰值功率为2.01 MW的稳定光脉冲输出,平均功率超过56 W,输出光束质量接近衍射极限(M_x^2=1.49,M_y^2=1.54)。

Abstract A main oscillation fiber amplification （MOFA） system is proposed, and the increasing of pulse signal peak power and the broadening of repetition frequency modulation range of the proposed system are studied experimentally. The electrical pulse modulation and the acousto-optic modulation are employed to modulate optical pulse sequence. Amplified spontaneous emission effect and self-excited oscillation of semiconductor seed source, which are generated in the process of small signal amplifying, are suppressed. The limitation of seed source to the repetition frequency of the proposed system is eliminated, and the repetition frequency can be tuned continuously in the range of 1-200 kHz. In the process of optical pulse modulation with the acousto-optic modulator, the acousto- optic Q-switch can effectively suppress the spectral broadening caused by self-phase modulation. The rod-like photonic crystal fiber with large mode field is used as the gain medium to increase the peak power of optical pulse and the beam quality of output light, and the nonlinear effect caused by high peak power is suppressed. Ultimately, the stable optical pulse output with the pulse width of 1.12 ns and the peak power of 2.01 MW is achieved, the average power is more than 56 W, and the beam quality of the output light is close to the diffraction limit （Mx^2=1.49,My^2=1.54）.