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• Few-layer NiTe 2 nanosheets are prepared by combining the convenient chemical synthesis and liquid phase exfoliation. • Two-dimensional semi-metallic NiTe 2 exhibits saturable absorption properties, which has been seldom reported. • Er-doped and Tm-doped mode-locked fiber lasers are realized using NiTe 2 -based tapered fiber saturable absorber, respectively. Two-dimensional transition metal dichalcogenides (TMDs) have been widely used in ultrafast optics. However, the traditional TMDs such as MoS 2 and WS 2 have narrow operating band and slow carrier recovery time, limiting their practical application. Among various kinds of TMDs, nickel ditelluride (NiTe 2) is a special type-II Dirac semi-metallic TMD material developed recently, showing great potential in ultrafast pulse generation due to its broadband optical response, ultrafast carrier recovery time, strong light-matter interaction and high chemical stability. Nevertheless, there has been no research reported on the NiTe 2 based saturable absorber (SA) and its application in the mode-locked laser at the 1.5 and 2 μm regions. In this work, few-layer NiTe 2 nanosheets were prepared and SA device was further fabricated by depositing them on a tapered fiber. The saturable absorption property of NiTe 2 SA was confirmed by using a balanced twin-detector measurement system. With the use of NiTe 2 SA, the Er-doped mode-locked fiber laser with a central wavelength of 1567.3 nm and a pulse width of 1.07 ps was achieved. Moreover, the Tm-doped mode-locked fiber laser with a central wavelength of 1966.08 nm was also obtained based on the NiTe 2 SA. These results show that NiTe 2 is a promising SA material for ultrafast pulse laser. [ABSTRACT FROM AUTHOR]

• Two-dimensional PdTe 2 is a novel saturable absorption material which has been rarely reported. • Few-layer PdTe 2 nanosheets are prepared by the simple and effective ultrasonic liquid exfoliation method. • Yb-doped mode-locked fiber laser with a pulse width of 887.2 ps is realized using PdTe 2 /PVA as the saturable absorber. In this work, two-dimensional few-layer palladium ditelluride (PdTe 2) nanosheets are produced by the simple and effective ultrasonic liquid exfoliation method and used as novel saturable absorber in an Yb-doped mode-locked fiber laser. The results show that the prepared flexible PdTe 2 /PVA composite film has a modulation of 3.7% and a saturation intensity of 77.6 MW/cm2. The obtained Yb-doped mode-locked fiber laser based on the film shows a pulse width of 887.2 ps with a repetition and central wavelength of 8.921 MHz and 1069 nm, respectively. So far, there has been few reports on PdTe 2 as saturable absorbers to realize mode-locked fiber lasers. The results suggest that two-dimensional PdTe 2 has great potential applications in nonlinear optics and ultrafast photonics. [ABSTRACT FROM AUTHOR]