Nonlinear optical properties of PtTe2 based saturable absorbers for ultrafast photonics

Abstract

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 μs 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.