Mode locking and multiwavelength Q-switching in a dumbbell-shaped fiber laser with a gold nanorod saturable absorber

A dumbbell-shaped fiber laser with dual-functional pulsed outputs is demonstrated using a filmy polyvinyl alcohol-based gold nanorods (GNRs) saturable absorber (SA), which can deliver mode-locked soliton and multiwavelength Q-switched pulse. The GNRs-SA is fabricated by seed-mediated method with a modulation depth of 4.1% and nonsaturable loss of 32.9%. When the fiber laser operates in mode-locked regime, stable fundamental solitons with a temporal width of 910 fs and repetition rate of 2.88 MHz are directly generated from the laser cavity. The corresponding spectrum is located at 1560.1 nm with a 3-dB bandwidth of 3.08 nm. When the laser operates in Q-switched regime, more than 5-wavelength oscillation is achieved. The repetition rate of Q-switched monotonically increases from 13.4 to 31.7 kHz and the pulse duration can be significantly narrowed from 6.07 to 3.12  μs by varying the pump power from 128 to 154 mW. The results further expand the applications of GNRs-SA to obtain versatile pulse sources in ultrafast laser field.