利用光纤布拉格光栅作为光谱滤波器来控制锁模掺铥光纤激光器的光谱形状和脉冲宽度,以及结合纤芯抽运高掺杂双包层掺铥光纤技术,实现了2µm波段重复频率为611.5 MHz 的皮秒脉冲激光输出.利用该高重复频率皮秒激光作为种子源,结合主振荡功率放大技术,研制出了百瓦量级全光纤全保偏结构皮秒脉冲掺铥光纤激光放大系统,得到了平均功率为203 W的线偏振皮秒脉冲激光输出,偏振消光比>15 dB,激光脉冲宽度为15 ps,相应的激光峰值功率为22 kW.该结果为目前国际上2µm波段全光纤结构超短脉冲激光器所产生的最高平均输出功率,为下一步2—5µm波段高功率中红外激光的产生提供了可靠的抽运源.%High-power ultrafast fiber lasers are important sources for a number of applications including material processing, pump source for optical parametric oscillator, and supercontinuum generation. Ultrafast thulium-doped fiber lasers, which extend the wavelength range of fiber lasers from 1.8 to 2.1 µm, have rapidly developed in the last several years and the average output power of the ultrafast thulium-doped fiber amplifiers has reached a hundredwatt level. The broad and smooth gain spectrum of thulium-doped fiber makes it a well-suited gain medium for generating the ultrashort laser pulses and broad wavelength tunability. However, previous reports on ultrafast thulium-doped fiber lasers and amplifiers were related to non-PM fiber configuration. These ultrafast thulium-doped fiber lasers and amplifiers may suffer the environmental instability, which means that these fiber sources are sensitive to externally-induced changes, like significant temperature variations and mechanical perturbations which will influence the fiber birefringence property. An effective method to eliminate this environmental instability is to build an all-PM, thulium-doped all-fiber MOPA configuration where the light polarizes only along the slow or fast axis in the PM fiber and PM-fiber components. Here, we demonstrate a high-power all-polarization-maintaining picosecond thulium-doped all-fiber master-oscillator power-amplifier (MOPA) system. The linearly-polarized thulium-doped all-fiber MOPA yields 203 W of average output power at central wavelength of 1985 nm with a polarization extinction ratio of >15 dB. The pulse duration of 15 ps at 611.5 MHz repetition-rate results in a peak-power of 22 kW in the final thulium-doped fiber power amplifier. To the best of our knowledge, this is the highest average output power ever reported for a picosecond-pulsed thulium-doped all-fiber laser at 2 µm wavelength. Furthermore, high-power linearly-polarized thulium-doped fiber laser with compact and simple design is greatly demanded for a variety of applications, such as coherent polarization beam combination, and frequency conversion in nonlinear crystals.
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