Er-doped Q-switched fiber laser with a black phosphorus/polymethyl methacrylate saturable absorber.

A stable Q-switched Er-doped fiber (EDF) laser is successfully obtained by using a black phosphorus (BP)/polymethyl methacrylate (PMMA) film as the saturable absorber (SA). To avoid the oxidization of nanomaterials, the BP nanoparticles are fabricated via a liquid-phase exfoliation method and then embedded into a PMMA film that possesses excellent optical transparency in the selected spectrum range. The modulation depth (MD) of the BP/PMMA film SA is 14.3% and the saturable intensity (I) is 6.9  MW/cm. By inserting the BP/PMMA film into the EDF laser cavity, we achieve the stable passive Q-switching operation over the wavelength range from 1561.21 nm to 1564.16 nm. The repetition rate increases from 10.348 kHz to 30.098 kHz, and the pulse duration decreases from 25.01 μs to 2.98 μs by altering the pump power from 9 mW to 90 mW. The maximum single pulse energy is 283.91 nJ. To the best of our knowledge, 283.91 nJ is the largest single pulse energy among the Q-switched fiber lasers with BP as the Q-switcher at the 1.5 μm wavelength region. The experimental results evidently show that the BP/PMMA film SA can work as a promising Q-switcher for large pulse energy fiber lasers.