Metal based passive saturable absorber embedded in chitin host polymer

Abstract

Pulse fiber laser is used in many applications such as those in high-speed communication, optical imaging, laser machining and fiber optic sensing. This is due to its simple setup, compact geometry, zero alignment configuration and cost-saving nature. Passive Q-switching is a technique to produce pulse fiber laser. Saturable absorbers play important roles in passive Q-switching technique. Research works on materials for saturable absorbers (SAs) have been conducted for decades. Saturable absorbers began with dyes or coloured glasses. Currently, Two-Dimensional (2D) materials are employed as the SA for the Q-switching. Metal-based SAs like gold, silver and copper are reported to exhibit excellent optical properties. However, reports on copper-based SA are still scarce despite their ultrafast response time, broad operation spectrum, and large third-order nonlinearity. Previously, researchers employed physical vapor deposition and chemical reduction that had drawbacks like using expensive methods, generating low volume of materials, and having issues such as toxicity, high cost, and impurities with reducing agents. Therefore, this study used three types of metal which were copper, aluminium, and brass. Three-dimensional filament was used to simplify the fabrication process of these metals. To do this, bio-compatible host polymer, materials characterisation, and the implementation in pulse fiber laser within a 1.5 μm region were employed. The three-dimensional metal filament was combined with metal: chitin as the bio compatible host polymer with a ratio of 1:4, 1:1.5 and 1:1. Regarding the performance of the SAs, the lowest threshold pump power for the passive Q-switching technique was obtained by copper-chitin 1:1 with 38.7mW. Meanwhile, the highest repetition rate and the lowest pulse width was by brass-chitin 1:4 with 165.60 kHz and 3.46 μs respectively. Besides, the highest signal to noise ratio (SNR) was 80.18 dB by copper-chitin 1:1. Finally, the SAs utilised were stable to produce pulse lasers through passive Q-switching, with the lowest SNR value of 64 dB.