Nanosecond passively Q-switched thulium/holmium-doped fiber laser based on black phosphorus nanoplatelets

Abstract

The generation of nanosecond pulses in a thulium/holmium-doped fiber laser passively Q-switched by a black phosphorus saturable absorber (BP-SA) was experimentally demonstrated. The high quality BP-SA with a modulation depth of ~24% was fabricated by depositing ~23 nm thickness of BP nanoplatelets onto a fiber ferrule. By inserting the BP-SA into a thulium/holmium-doped fiber laser cavity, stable Q-switched operation was achieved with the maximum pulse energy up to 632.4 nJ, the shortest pulse width of 731 ns and pulse repetition rates varying from 69.4 to 113.3 kHz. These results suggested that BP could be developed as an effective SA for pulsed laser operation at 2 μm.