Mode-locking in Er-doped fiber laser with reduced graphene oxide on a side-polished fiber as saturable absorber

In this work, the generation of highly stable mode-locked pulses from a side-polished fiber (SPF) embedded with graphene oxide (rGO) nanoparticles (NPs) is proposed and demonstrated. The rGO NPs are obtained from a graphene oxide solution prepared using Hummer's technique, before being reduced by a hydrothermal route. The rGO NPs, suspended in the form of a solution, are then drop-casted onto the SPF. The SPF is fabricated by polishing away the cladding layer of a single-mode fiber section, leaving the core exposed and allowing the evanescent field of the signal propagating through the fiber to interact directly with the NPs. The SPF is integrated into an erbium doped fiber laser (EDFL) cavity, and the strong nonlinear optical response and spectral filtering by the rGO NPs as well as total anomalous dispersion of the laser cavity generates highly stable soliton mode-locked pulses with visible Kelly's sidebands at 1544.02 nm. The output pulses have a pulse repetition rate of 16.79 MHz and pulse duration of 1.17 ps throughout the mode-locking operation range of 64.44-280.5 mW. The rGO NP coated SPF in this work demonstrates the viability and performance of the SPF for mode-locked pulse generation via evanescent field interactions.