Passive Q-switched Erbium-doped fiber laser with graphene-polyethylene oxide saturable absorber in three different gain media

A Q-switched Erbium-doped fiber laser (EDFL) is proposed and demonstrated using graphene/polyethylene oxide thin film as a passive saturable absorber. The multi-layered graphene saturable absorber is incorporated into ring cavity of EDFL. Three different gain media are tested for the EDFL and they are 7 m long silica Erbium-doped fiber (EDF) with 400 ppm Erbium concentration, 4.5 m long EDF with 2,000 ppm Erbium concentration and 0.5 m long Bismuth EDF with 3,000 ppm Erbium concentration. The threshold pump powers for stable and seft-starting Q-switching are 33.7, 98.5 and 59.5 mW for 400, 2,000 and 3,000 ppm EDF, respectively. Corresponding pulse repetition rates are 24.2, 9.8 and 22.5 kHz at the threshold pump powers. The shortest pulse width of 2.48 mu s is obtained with EDFL configured with 0.5 m long Bismuth EDF. The highest pulse energy of 40.69 nJ is obtained at pump power of 98.5 using 2,000 ppm silica EDF.