Abstract
Despite extensive applications ranging from optoelectronic devices to flexible devices, two-dimensional layered materials used as ultrafast optical modulation materials have suffered from limited operation wavebands due to their intrinsic bandgap. Here, we investigate the nonlinear optical (NLO) response of group IIIA/IVA monochalcogenides XTe (X = Ga and Ge), which exhibit a remarkable saturable absorption response at a broadband wavelength. By using a liquid phase exfoliation technique, we prepare XTe nanosheets with few-layer thickness in a deionized water solvent and investigate their NLO responses at 800 nm, 1.5 µm, and 2 µm, respectively. Both GaTe and GeTe nanosheets exhibit ultrafast saturable absorption at 800 nm with 32.4 μJ (48.4 µJ) incident intensity. After preparing microfiber-based nanosheet optical modulators, their saturable absorptions are measured at 1.5 µm and 2 µm. The GaTe-SA possesses a little bit higher modulation depth (42.3% at 1.5 µm/30.7% at 2 µm) than the GeTe-SA (30.5% at 1.5 µm/8.3% at 2 µm) at two wavelengths. The lifetime of GaTe and GeTe nanosheets is measured to be 2.8 ps and 3.3 ps, respectively. In addition, we further examine their saturable absorption via incorporating them into an erbium- and a thulium-doped fiber laser system and obtain stably passively mode-locked pulse trains, respectively. The distinct NLO properties indicate a large potential of XTe nanosheets in the development of an ultrafast optical mode locker with a wideband operation wavelength.
Highlights
Self-starting passive mode-locking operation in an erbium-doped fiber laser (EDFL) and a thulium-doped fiber laser (TDFL) system indicates that both gallium telluride (GaTe) and germanium telluride (GeTe) nanosheets could be employed as remarkable saturable absorption materials in wideband pulsed laser systems
We have shown that the GaTe and GeTe bulk could be exfoliated to few-layer nanosheets with high quality in a deionized water solvent without using any organic solvent
The results indicate that using deionized water as a solvent is a potential approach to exfoliate high quality GaTe and GeTe nanosheets with few-layer thickness and is beneficial for further expanding the range of their applications in different fields
Summary
The ultrashort pulse laser has attracted significant interest due to its wide applications such as precision machining, health care, and environmental sensing, which are underway with remarkable efforts. Recently, research studies have demonstrated that part of two-dimensional layered materials (2DLMs) can be great candidates for versatile and reliable saturable absorbers (SAs) in pulsed laser systems. As for an ideal SA, it should possess properties such as ultrafast nonlinear optical (NLO) response, broadband optical absorption, large modulation depth, small saturable intensity, as well as high damage threshold, which are main factors to transfer continuous waves into stable pulsed trains. the fabrication process of SAs is one of the most decisive factors in actual applications, which requires features such as low-cost, easy fabrication, and high repeatability. According to the above-mentioned requirements, uniform and atomically thin 2DLMs with high environmental stability and outstanding NLO response are desirable for ultrafast pulse generation in laser systems. Nanosheets applied in optoelectronic devices in previous works are mainly prepared by the mechanical exfoliation method with random size and low yield Their NLO properties and applications for ultrafast photonics have not been studied yet. Benefiting from the development of the liquid phase exfoliation (LPE) technique, researchers can obtain few layered nanosheets (NSs) with high yield, which pave the way for their study in NLO properties and optical devices. We demonstrate that deionized water could be an ideal solvent to exfoliate XTe nanosheets with high crystal quality and few-layer thickness. We characterize their NLO responses at 800 nm, 1.5 μm, and 2 μm, respectively. Self-starting passive mode-locking operation in an erbium-doped fiber laser (EDFL) and a thulium-doped fiber laser (TDFL) system indicates that both GaTe and GeTe nanosheets could be employed as remarkable saturable absorption materials in wideband pulsed laser systems
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