Passive technique of generating soliton mode-locked in thulium/holmium doped fiber laser employing MXene/Polyvinyl alcohol film

Abstract

The present study proposes and demonstrates stable passive mode-locking in a laser operating at a wavelength of 2.0 μm by coupling a vanadium carbide MXene/polyvinyl alcohol (V2C/PVA) film, acting as a saturable absorber (SA), into the cavity of a Thulium/Holmium co-doped fiber laser (THDFL). The V2C/PVA film was successfully fabricated through a solution casting method. Initially, the V2C MXene was prepared using the molten salt method, wherein the aluminium (Al) layers were extracted from the V2AlC MAX phase precursor. The fabricated V2C/PVA film SA exhibits favourable nonlinear absorption properties, with recorded values of approximately 50% for modulation depth, 1 kW/cm2 for saturation intensity, and 50% for non-saturable loss. Achieving mode-locking at 1958.97 nm required a pump power of 283.5 mW, resulting in a 3-dB bandwidth of 4 nm. The SA generated stable pulses with an 18.69 MHz repetition rate, a pulse width of 1.6 ps, and a high signal-to-noise ratio (SNR) of around 60 dB. The research findings will pave the way for the application of V2C/PVA film SA in the field of ultrafast lasers.