Poly(3-hexylthiophene-2,5-diyl) regioregular (P3HT) thin film as saturable absorber for passively Q-switched and mode-locked Erbium-doped fiber laser

•Poly(3-hexylthiophene-2,5-diyl) regioregular (P3HT) organic semiconductor as saturable absorber.•A stable Q-switching pulses was achieved.•A stable mode-locking soliton pulses was achieved.•Mode-locked laser operated at repetition rate of 1.838 MHz with 2.62 ps pulse width. Q-switched and mode-locked Erbium-doped fiber lasers (EDFLs) were demonstrated using poly(3-hexylthiophene-2,5-diyl) regioregular (P3HT) organic semiconductor in the form of thin film as a saturable absorber (SA). The P3HT thin film is cut into small pieces and sandwiched between two ferrules in EDFL cavity to generate a stable Q-switching and mode-locking pulse train. By increasing the 980 nm pump power from 63 mW to 125 mW, the repetition rate of the EDFL increases from 62.97 kHz to 78.63 kHz while the pulse width decreases from 5.52 µs to 3.79 μs. The maximum pulse energy of 15.05 nJ is generated with repetition rate and pulse width of 78.63 kHz and 3.79 μs, respectively. Meanwhile, self-starting mode-locked EDFL arises as the pump power raises from 125 mW to 187 mW. As the pump power increases to the maximum, the repetition rate is almost constant of 1.838 MHz and pulse width of 2.62 ps are observed. The mode-locked EDFL operated at 1563 nm wavelength. This experiment shows that P3HT SA can be used to generate stable Q-switched and mode-locked pulsed lasers.