Nonlinear optical properties of PtTe₂ based saturable absorbers for ultrafast photonics

Platinum ditelluride (PtTe2) has many applications in phototransistors, photodetectors, photocatalysis and other fields due to its interesting semiconductor-to-semimetal transition property, ultrashort excited carrier lifetime, high carrier mobility, excellent air stability, and so on. However, the ultrafast nonlinear optical properties of PtTe2 and its application in ultrafast photonics have been rarely explored so far. In this work, PtTe2 nanosheets were prepared and two kinds of saturable absorbers (SAs) were further fabricated, namely the PtTe2/PVA film and PtTe2 coated tapered fiber. The results showed different nonlinear absorption properties for the two SAs. The modulation depth and saturation intensity were determined to be 0.9% and 55.7 MW cm(-2) for the PVA film, and 8.9% and 1.39 GW cm(-2) for the tapered fiber, respectively. More importantly, Q-switched and mode-locked Er-doped fiber lasers were realized using the PtTe2/PVA film and PtTe2 coated tapered fiber SAs, respectively. The pulse widths of the Q-switched and mode-locked fiber lasers are 2.63 mu s and 959 fs, respectively. These results confirm that PtTe2 has great potential in ultrafast photonic applications, and moreover, the PtTe2 coated tapered fiber SA is more suitable for mode-locked fiber lasers because of its lower nonsaturable absorption loss and larger modulation depth by contrast to the PVA film SA.