Passively Q-switched and mode-locked laser generation in 3 μm fluoride fibers based on tellurium/graphene heterojunction saturable absorber

Faced with the problem that the low modulation depth and saturation intensity of mid-infrared saturable absorbers (SAs) make it difficult to achieve higher pulse energy passively Q-switched, this paper successfully produced Qswitched and mode-locked mid-infrared 3 μm lasers in fluoride fiber lasers using tellurium/graphene (Te/G) heterojunctions as SAs. Stable Q-switched pulses are achieved at low pump power, with a maximum repetition rate of 106.3 kHz and a shortest pulse width of 2.36 μs. The corresponding maximum output power reaches 63.1 mW, with a slope efficiency of 25.5%, and the corresponding pulse energy is 0.594 μJ. Moreover, as the pump power increases, the laser enters the continuous-wave mode-locked state. The maximum average output power of the 3 μm mode-locked laser reaches 149.3 mW at 1.19 W, with a slope efficiency of 10.3%. This represents the first successful demonstration of passively Q-switched and mode-locked laser in fluoride lasers operating in the mid-infrared 3 μm region using Te/G heterojunction SA. The experimental results demonstrate that heterojunctions are an effective method to improve nonlinearity, which is a promising approach to achieve high-efficiency pulsed laser.