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提出了基于主振荡功率放大(MOPA)结构的皮秒光纤激光系统。该系统将重复频率为29.87 MHz的半导体可饱和吸收镜被动锁模光纤激光器作为种子源。采用预放系统并结合声光调制器将种子源的重复频率降至574kHz。MOPA结构基于棒状光子晶体光纤(PCF),利用PCF大模场、高增益的特点直接对脉冲宽度为30ps的脉冲进行放大,有效抑制了自相位调制效应引起的光谱展宽。研究结果表明,所提系统的5dB光谱线宽与光脉冲峰值功率成比例,该系统最终输出了近衍射极限、峰值功率为3.4 MW的皮秒脉冲(输出功率为20 W时,光束质量因子M2=1.01),最高平均输出功率为21.86 W,脉冲宽度为11.1ps,中心波长为1030.74nm,5dB光谱线宽为1.75nm。
A picosecond fiber laser system based on the main oscillator power amplifier (MOPA) is proposed. The system uses a semiconducting saturable absorption mirror passively mode-locked fiber laser with a repetition frequency of 29.87 MHz as the seed source. The pre-release system and the acousto-optic modulator are used to reduce the seed source repetition rate to 574 kHz. Based on the rod-shaped photonic crystal fiber (PCF), the MOPA structure directly amplifies the pulse with a pulse width of 30 ps by utilizing the large mode field and the high gain of the PCF, effectively suppressing the spectral broadening caused by the self-phase modulation effect. The results show that the proposed system has a 5 dB spectral linewidth that is proportional to the peak power of the optical pulse. The system finally outputs a near-diffraction-limited picosecond pulse with a peak power of 3.4 MW (at a beam power of 20 W, the beam quality factor M2 = 1.01). The maximum average output power was 21.86 W, the pulse width was 11.1 ps, the center wavelength was 1030.74 nm, and the 5 dB spectral width was 1.75 nm.