Efficiency of passive Q-switched regimes in erbium-doped fiber lasers using polarization-dependent and independent isolators: a DFT study of V2CTx band structure and optical properties

In this study, we demonstrate the integration of novel two-dimensional (2D) vanadium carbide (V 2 CT x ) MXene nanosheets as saturable-absorber (SA) into an erbium-doped fiber laser (EDFL) cavity, enabling both polarization-independent passive Q-switched (PI-PQS) and polarization-dependent passive Q-switched (PD-PQS) pulse operations. The V 2 CT x nanosheets were synthesized then the morphogy as well structure of the prepared nanosheets were characterized through scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. In PI-PQS operation, pulse generation was initiated at a pump power of 17.5 mW, while in PD-PQS operation, the pulse operation was initiated at 92.9 mW. With a maximum pump power of 312.5 mW, the pulse duration and average output power were 4.92 µs and 1.19 mW for the PI-PQS EDFL and 4.25 µs and 2.09 mW for the PD-PQS EDFL, respectively. Furthermore, employing density functional theory (DFT) calculations, we obtained the band structure and optical properties of V 2 CT x , confirming its importance as an SA in EDFL. These results validate the optimized performance of PD-PQS EDFL relative to PI-PQS EDFL. This study further suggests that other MXenes may have potential as SAs in EDFLs for producing Q-switched pulses, warranting further investigation.