Dai Ruihong, Meng Yafei, Li Yao, Qin Jiarong, Zhu Shining, Wang Fengqiu
Opt Express. 2019 Feb 4;27(3):3518-3527. doi: 10.1364/OE.27.003518.
Mode-locked oscillators with highly tunable output characteristics are desirable for a range of applications. Here, with a custom-made tunable filter, we demonstrate a carbon nanotube (CNT) mode-locked thulium fiber laser with widely tunable wavelength, spectral bandwidth, and pulse duration. The demonstrated laser's wavelength tuning range reached 300 nm (from 1733 nm to 2033 nm), which is the widest-ever that was reported for rare-earth ion doped fiber oscillators in the near-infrared. At each wavelength, the pulse duration can be regulated by changing the filter's bandwidth. For example, at ~1902 nm, the pulse duration can be adjusted from 0.9 ps to 6.4 ps (the corresponding output spectral bandwidth from 4.3 nm to 0.6 nm). Furthermore, we experimentally and numerically study the spectral evolution of the mode-locked laser in presence of a tunable filter, a topic that has not been thoroughly investigated for thulium-doped fiber lasers. The detailed dynamical change of the mode-locked spectra is presented and we observed gradual suppression of the Kelly sidebands as the filter's bandwidth is reduced. Further, using the polarization-maintaiing (PM) cavity ensures that the laser is stable and the output laser's polarization extinction ratio is measured to exceed 20 dB.
具有高度可调输出特性的锁模振荡器在一系列应用中都很受欢迎。在此，我们利用定制的可调滤波器，展示了一种碳纳米管（CNT）锁模铥光纤激光器，其波长、光谱带宽和脉冲持续时间均可广泛调谐。所展示的激光器波长调谐范围达到300 nm（从1733 nm至2033 nm），这是近红外波段稀土离子掺杂光纤振荡器所报道的最宽调谐范围。在每个波长处，脉冲持续时间可通过改变滤波器带宽来调节。例如，在~1902 nm处，脉冲持续时间可从0.9 ps调节至6.4 ps（相应的输出光谱带宽从4.3 nm至0.6 nm）。此外，我们通过实验和数值方法研究了存在可调滤波器时锁模激光器的光谱演化，这一主题在掺铥光纤激光器中尚未得到充分研究。我们展示了锁模光谱的详细动态变化，并观察到随着滤波器带宽减小，凯利边带逐渐受到抑制。此外，使用保偏（PM）腔可确保激光器稳定，且测得输出激光的偏振消光比超过20 dB。
