Erbium doped fiber lasers utilizing gadolinium oxide, neodymium oxide and samarium oxide as passive saturable absorbers

Abstract

Erbium doped fiber laser (EDFL) plays an important role in generating laser in the 1.5-micron region which contributes to many applications such as material processing, optical communication and biomedical. The main goal of this research is to improve the passive technique in generating mode-locked and Q-switched pulsed fiber laser. The passive technique uses a saturable absorber (SA) as a passive optical loss modulator for the creation of pulses inside the laser cavity. Three rare earth oxides (REO) are chosen to be utilised as the saturable absorbers that are Gadolinium Oxide (Gd2O3), Neodymium Oxide (Nd2O3) and Samarium Oxide (Sm2O3). The REO-based SA was fabricated in the form of thin film by mixing it into polyvinyl alcohol (PVA) aqueous solution to produce a free-standing polymer composite SA film. The characterisations of SA films include physical and optical properties. The physical properties were characterised using field emission electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). The characterisations of optical properties include linear and nonlinear absorptions. The Q-switched pulses were generated by inserting the SA film into the laser cavity. The addition of 100 m single mode fiber (SMF) with group dispersion delay (GVD) of -21.7 ps2/km into the laser cavity increased its nonlinearity to balance the total cavity dispersion, consequently, promoted the mode-locking action. The performance of pulsed lasers were analysed and discussed in term of the pulsed laser parameters. The mode-locked pulsed laser with Sm2O3 SA had successfully generated stable pulses with the minimum pulse width of 3.4 ps. Gd2O3 and Nd2O3 SA films generated the mode-locked laser pulses with pulse widths of 3.82 ps and 4.62 ps respectively. The Q-switched laser performances acquired using the three SA films also show desirable laser outputs. Based on the performances of Q-switched and mode-locked pulsed lasers, this research was successfully done with less tedious SA preparation and simple laser cavity setup, thus it have a good potential for photonics applications.