Short pulse laser generation in 1.5-micron region using transition metal-based saturable absorber / Norizan Ahmed

Short-pulse fiber lasers have significant applications in many areas, including optical communication, biomedical, eye surgery, laser cutting, range finding, and spectroscopy. It outperforms bulk lasers in terms of flexibility and reliability, offering a promising platform for future fiber laser technology. The generation of these pulses, operating in a Q-switched and mode-locked regime, can be categorized as active or passive. The passive approach utilizing a saturable absorber (SA), an optical component that exhibits an intensity-dependent transmission, has gained great interest due to its simplicity of structure, low cost (without the need for expensive and complex electrically-driven modulators), and ability to achieve narrow pulse durations, high output power, and perfect beam quality. This thesis demonstrated the generation of a Q-switched and mode-locked laser through a passive approach based on a saturable absorber (SA). The newly developed SA was integrated into an erbium-doped fiber laser (EDFL) cavity to generate pulses operating in the 1.5-micron region. The proposed SAs are based on two dimensional (2D) materials classified as transition metal oxide (TMO), transition metal dichalcogenide (TMD), and transition metal chalcogenide (TMC), whose elements are titanium dioxide (TiO2), iron disulfide (FeS2), and silver sulfide (Ag2S), respectively. Their versatile properties, which are desired in photonics and optoelectronics applications, inspired this work. The SA is fabricated using the liquid phase exfoliation method. The fabricated SA, in the form of a thin film, is then physically characterized using a field emission scanning electron microscope (FESEM) and electron dispersion spectroscopy (EDS) to confirm the presence of the element in the device. The optical characterizations such as linear and nonlinear absorption measurements are also carried out. The SA device is integrated into the laser cavity to validate its performance. This is accomplished by sandwiching a piece of the SA film between two fiber ferrules. Overall, the potential of Ag2S as a promising Q-switcher has been demonstrated through the generation of a Q-switched pulse with the highest repetition rate, highest output power, and highest pulse energy of 93.81 kHz, 5.07 mW, and 54.05 nJ, respectively. As for the mode-locked operation, the results show that FeS2 is capable of providing a pulsed laser output with the shortest pulse width of 2.53 ps, the highest output power of 10.65 mW, and the highest pulse energy of 5.69 nJ. These findings show convincingly that the passive devices proposed in this work can generate short-pulse lasers and, in photonic applications, these materials hold great potential.