Tm3+-Doped Harmonic Dissipative Soliton Mode-Locked Fiber Laser at 1.93 $\mu$ m Based on Tungsten Disulfide in Anomalous Dispersion Regime

Zhen Tian,Chun-Nien Liu,Cheng-Kai Yao,Haimiao Zhou,Liqiang Zhang,Min Zhao,Shien-Kuei Liaw,Dong Yan,Nan-Kuang Chen,Huishan Yu

doi:10.1109/access.2019.2955312

Abstract

We report a harmonic dissipative soliton $1.93~\mu \text{m}$ thulium fiber laser based on a tungsten disulfide (WS2) saturable absorber (SA) in the anomalous dispersion regime. The multilayer WS2 nanosheets were prepared by liquid phase exfoliation method and the SA was fabricated by dropping WS2 solution onto a gold mirror. The transferred WS2 SA had a modulation depth of 2.5% and a saturation intensity of 0.82 MW/cm2. By incorporating the SA into a linear Tm3+ fiber laser cavity, harmonic mode-locked dissipative soliton laser was achieved at 1930 nm with the spectral width of 8 nm, the pulse energy of 3 nJ, the pulse width of 3.6 ns, and the repetition rate of 56.3 MHz. Based on the experimental results, it is shown that with the presence of harmonic mode-locking in $2~\mu \text{m}$ wavelength region, the multilayer WS2 serving as a SA was verified to be a good candidate for broadband high-energy mode-locking. The order of the harmonic dissipative soliton mode-locked pulses remains the same along with the increasing pump power.

Highlights

In recent years, passively mode-locked ultrafast lasers operating in the 2 μm region based on thuliumdoped fibers have been intensively investigated for the important applications in remote sensing, medical surgery, industrial micromachining, and scientific experiments [1]–[4]
In contrast to conventional harmonic mode-locking where the harmonic number changes with pump power, the harmonic frequency of the WS2 mode-locked fiber laser in this work remains the same (3rd harmonic) when the pump was increased to 950 mW from 400 mW or was decreased to 80 mW from 400 mW
The reason why the order of the harmonic mode-locked pulses remains the same with increasing pump power is ascribing to the high laser output coupling ratio (96%) and which results in a smaller cavity quality factor and a higher cavity loss in cavity [14]

Summary

Introduction

Passively mode-locked ultrafast lasers operating in the 2 μm region based on thuliumdoped fibers have been intensively investigated for the important applications in remote sensing, medical surgery, industrial micromachining, and scientific experiments [1]–[4]. Most of the research works about DS were carried out in the 1 μm and 1.5 μm wavelength regions and only quite a few investigations for DS were proposed at 2 μm. This is because the dissipative solitons were exclusively found in all normal-dispersion mode-locked lasers theoretically [15]–[17]. The commercially available gain fibers (GFs) in the 2 μm wavelength region owns relatively large anomalous dispersion, which results in 2 μm mode-locked lasing in the conventional soliton regime.

Methods

Results

Conclusion