Electro-deposited transition metal dichalcogenides absorbers for producing Q switched and mode-locked fiber lasers / Lee Lian Hong

Lee , Lian Hong (2024) Electro-deposited transition metal dichalcogenides absorbers for producing Q switched and mode-locked fiber lasers / Lee Lian Hong. PhD thesis, Universiti Malaya.

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Abstract

This PhD research work will use two-dimensional (2D) materials especially transition metal dichalcogenides (TMD) such as MoS2, MoSe2 and MoTe2 as saturable absorber (SA) to passively generate Q-switched and Mode-locked fiber lasers. Previously, the above mentioned TMDs based SAs were prepared using conventional methods including liquid-phase exfoliation, PVA film, drop-cast technique and mechanical exfoliation. In this research, a new method is being proposed to fabricate the mentioned TMDs and this method involves the technique of electro-deposition. This method has been applied in other research field but has not been utilized in the specific domain of Q-switched and mode-locked fiber laser. The advantage of this electro-deposition method is that it can produce a more homogeneous and more stable SA for the generation of the Q-switched and mode-locked fiber laser. The fabricated SAs will be used in the designated experiment setup to achieve Q-switched and mode-locked fiber laser by sandwiching the SAs in between two fiber ferrules. Furthermore, the characterization of the fabricated SAs is performed using field emission scanning electron microscope (FESEM), electron dispersion spectroscopy (EDS) and X-ray diffraction (XRD) to check the surface morphology of the SAs and to confirm the presence of 2D TMD materials in the fabricated SA. Moreover, the linear absorption and modulation depth are also presented for each of the fabricated SAs. Finally, this research will analyze the Q-switched and mode-locked performance of the system using the fabricated SAs. Ultrashort pulse fiber lasers operating at 1.55- and 2-micron regions with various performances are successfully achieved in this work. For instance, the prepared MoS2 thin film exhibits the saturable absorption characteristic of 3.4%, when this MoS2 SA was introduced into an Erbium-doped fiber laser (EDFL) cavity, a stable Q-switched pulse at 1559.4 nm was achieved by adjusting the pump power above the threshold of 51.67 mW. The pulse has a maximum repetition frequency of 89.89 kHz, minimum pulse width of 4.75 μs and maximum pulse energy of 15.03 nJ at 105.27 mW pump power. Mode-locked pulse is also obtained at 1560.8 nm when the cavity length was extended to 106 m. The repetition frequency and pulse width of the mode-locked pulse were 1.88 MHz and 1.47 ps respectively. To the best of our knowledge, this is the first time that Q-switched and mode-locked pulses have been obtained in a fiber laser based on this new electrodeposition method.

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