Nanotubes in Chitin Mode Locker for Passive Mode-Locked Fibre Laser in 2.0 mu m Region

This research demonstrated an ultrafast passively mode-locked thulium-holmium doped fibre laser (THDFL) using a carbon nanotube (CNT)-chitin composite film as a saturable absorber (SA). The CNTs were fabricated using ultrasonic-assisted liquid-phase exfoliation, and the chitin biopolymer was derived from oyster mushrooms (Pleurotus Ostreatus). The free-standing SA successfully performed a mode-locking operation at a threshold input pump power of 203 mW with an operating wavelength of 1908.53 nm. The generated mode-locked pulses had repetition rate, pulse width, and signal-to-noise ratio (SNR) values of 16 MHz, 1.1 ps, and 69 dB, respectively. The work demonstrates the potential of CNTs embedded in chitin biopolymer as a sustainable and environmentally friendly SA for a wide range of applications, particularly for pulsed lasers.