Tin Telluride Quantum Dots as a Novel Saturable Absorber for Q-Switching and Mode Locking in Fiber Lasers

Tin telluride (SnTe) quantum dots (QDs) have attracted considerable interest in the optoelectronic field owing to their favorable properties over conventional QDs, such as a relatively large Bohr radius (95 nm) and low toxicity level. However, till date, the nonlinear optical properties and ultrafast photonics applications of SnTe QDs have remained unexplored. In this study, SnTe QDs with an average diameter of 74 nm (smaller than the Bohr radius of SnTe) are fabricated via a liquid-phase exfoliation method. Consequently, the nonlinear saturable absorption properties of such SnTe QDs are explored by realizing a modulation depth of 2.2% and saturable intensity of 1.67 GW cm⁻². The prepared QDs are then used as saturable absorber (SA) in the erbium-doped fiber laser ring cavity system. Moreover, Q-switched and mode-locked laser pulses with a pulse width of 1.81 µs and 691 fs are generated, respectively. Harmonic mode-locking with a high repetition rate of 62.1 MHz (fifth order) is experimentally realized. This is the first demonstration, to the authors’ knowledge, of using SnTe QDs-SA for generating ultrafast laser pulses along with high-repetition-rate harmonic mode-locking pulses. Therefore, this study will establish a new research scope for SnTe QDs in ultrafast photonics, nonlinear photonics, frequency combs, and optical communications.