Graphene based passive q-switcher in erbium doped fiber laser

Abstract

Graphene is known as the material of wonder for its extraordinary properties that can be utilized for the technology advancement in various fields. In this work, graphene based saturable absorber (SA) was used for pulsed laser generation. The SA was integrated within an erbium-doped fiber laser (EDFL) ring cavity for passive Q-switching, generating pulsed laser. Passively Q-switched EDFL has been achieved by using various materials as SAs, with the current trend focuses on the 2-Dimensional (2D) materials. Graphene was the most favourable for this research due to its low-cost and simple fabrication compared to the complex fabrication process, narrow wavelength range, and unstability in ambient temperature of other 2D materials. Two types of graphene were used as the starting material for SA fabrication in this work: electrochemical exfoliated (ECE) graphene (GrE) and graphene filament (GrF). The two graphene were combined with host polymers with the graphene : polymer ratios of 1 : 4, 2 : 3 and 2.5 : 2.5 to develop free standing films for easy integration within laser ring cavity. The host polymers used were polyvinyl alcohol (PVA) and chitin in which GrE used both to develop GrE-PVA SA and GrE-chitin SA respectively, while GrF was combined with chitin to develop GrF-chitin SA. The absence of PVA as host polymer for GrF-based SA was due to the usage of tetrahydrofouran (THF) in the preparation of the filament that reacted poorly with the PVA, inhibiting the formation of a free-standing SA film. Chitin is an alternative host polymer to produce a more environmental-friendly SA. Comparing the performance of the SAs, the lowest threshold pump power for the Q-switching activity was 16.7 mW, obtained by GrF-chitin 2.5 : 2.5 while the highest repetition rate and lowest pulse width were obtained by GrF-chitin 2 : 3 at 121.4 kHz and 3.32 μs respectively. On the other hand, the highest signal-to-noise ratio (SNR) was 88.88 dB which was generated by GrE-PVA 2 : 3. Ultimately, the SAs used in this work is deemed stable for the use of pulsed laser generation by passive Q-switching as the lowest SNR value has also been considerably high at 64.64 dB.