Laser &Fiber Electronics Group, Faculty of Electronics, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland.
Sci Rep. 2017 Apr 3;7:45491. doi: 10.1038/srep45491.
In this work, we demonstrate a comprehensive study on the nonlinear parameters of carbon nanotube (CNT) saturable absorbers (SA) as a function of the nanotube film thickness. We have fabricated a set of four saturable absorbers with different CNT thickness, ranging from 50 to 200 nm. The CNTs were fabricated via a vacuum filtration technique and deposited on fiber connector end facets. Each SA was characterized in terms of nonlinear transmittance (i.e. optical modulation depth) and tested in a Thulium-doped fiber laser. We show, that increasing the thickness of the CNT layer significantly increases the modulation depth (up to 17.3% with 200 nm thick layer), which strongly influences the central wavelength of the laser, but moderately affects the pulse duration. It means, that choosing the SA with defined CNT thickness might be an efficient method for wavelength-tuning of the laser, without degrading the pulse duration. In our setup, the best performance in terms of bandwidth and pulse duration (8.5 nm and 501 fs, respectively) were obtained with 100 nm thick CNT layer. This is also, to our knowledge, the first demonstration of a fully polarization-maintaining mode-locked Tm-doped laser based on CNT saturable absorber.
在这项工作中，我们研究了碳纳米管（CNT）饱和吸收体（SA）的非线性参数作为纳米管薄膜厚度的函数。我们制作了四组具有不同 CNT 厚度的饱和吸收体，范围从 50nm 到 200nm。CNTs 通过真空过滤技术制造，并沉积在光纤连接器端面上。每个 SA 都从非线性透过率（即光调制深度）方面进行了表征，并在掺铥光纤激光器中进行了测试。我们表明，增加 CNT 层的厚度会显著增加调制深度（200nm 厚的层可达 17.3%），这强烈影响激光的中心波长，但适度影响脉冲持续时间。这意味着，选择具有定义的 CNT 厚度的 SA 可能是一种有效调节激光波长的方法，而不会降低脉冲持续时间。在我们的设置中，以带宽和脉冲持续时间（分别为 8.5nm 和 501fs）为基准，获得了最佳性能的是 100nm 厚的 CNT 层。这也是，据我们所知，首次基于 CNT 饱和吸收体展示的全偏振保持锁模掺铥光纤激光器。
