Growth of magnetic binary metal oxides on reduced graphene oxide sheets and its application as saturable absorber in mode-locked Tm/Ho Co-doped fiber laser

Abstract In this work, a simple yet efficient method of growing magnetic binary metal oxides of CuO/Fe2O3 nanoparticles on reduced graphene oxide (rGO) sheets using the hydrothermal method was demonstrated. The rGO-CuO/Fe2O3 nanocomposite was characterized by X-ray diffraction (XRD), Raman, field emission scanning electron microscope (FESEM) and high-resolution transmission electron microscopy (HRTEM) analysis. The nonlinear optical absorption characteristics of the rGO-CuO/Fe2O3 nanocomposite exhibited a modulation depth and saturation intensity of 12.5% and 1.0 kW/cm2, respectively. The rGO-CuO/Fe2O3 nanocomposite in the solution form were drop-casted onto a microfiber to form a saturable absorber (SA) which was then incorporated into a Thulium-Holmium (Tm/Ho) co-doped fiber laser (THDFL) cavity. The mode-locked output was generated at 1917 nm with pulse duration of 1.34 ps and repetition rate of 11.36 MHz. The obtained RF spectrum revealed that the mode-locked laser was stable with a signal to noise ratio (SNR) of about 63 dB. This work demonstrated the capability of rGO-CuO/Fe2O3 nanocomposite as an SA to induce stable mode-locking in a THDF fiber laser cavity.