Q-switched fiber laser with tungsten disulfide saturable absorber prepared by drop casting method

Abstract

Abstract-We experimentally demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) operation by using a saturable absorber (SA) based on tungsten disulfide (WS2). By depositing a WS2 thin film layer at the end of an optical fiber ferrule, we fabricated an SA device. The SA is incorporated into an Erbium-doped fiber laser (EDFL) cavity to generate a Q-switching pulses train operating at 1559.8 nm. As a result, stable passively Q-switched EDFL pulses with a maximum output pulse energy of 123.2nJ, repetition rate of 104.1kHz, and pulse width of 9.61μs are achieved when the input pump power is 142.1mW at a wavelength of 980nm. (SAs). Compared with SESAMs, these emerging materials possess the excellent virtues of a broader operation wavelength band, more excellent nonlinear optical response, and easier fabrication. Among them, a group of semiconducting TMDs, like tungsten disulfide (WS 2 ) and molybdenum disulfide (MoS 2 ), have stood out for their typical graphene-like two-dimensional (2D) layered structure, unique thickness-dependent bandgap and stronger light-matter interaction than graphene [9].Most of the reported Q-switched lasers have low output power. For instance, Wu et al. demonstrated a Q-switched EDFL using WS 2 nanosheets, which were prepared using a liquid-phase exfoliation method and embedded in a polyvinyl alcohol (PVA) film [10]. Through a mechanical exfoliation technique, the WS 2 also can work as SA for Qswitching generation [11]. However, the signal-to-noise ratio of the formatted pulse is only up to 43dB. Chen et al. demonstrated high damage WS 2 SA and obtained pulse energy reaching 68.5nJ [12]. In another work, the WS 2 based Q-switched EDFL was demonstrated to generate a cylindrical-vector beam [13]. By combining WS 2 and * E-mail: yasin@fst.unair.ac.id SESAM, Chen et al. successfully generated a modelocked pulse laser at the C-band region [14]. In this letter, we demonstrate a Q-switched EDFL using WS 2 based SA, which was prepared using a drop casting method. Compared to the previously reported, this paper has successfully demonstrated a higher repetition rate and short pulse width size [15]. Moreover, the proposed laser produced a higher maximum pulse energy of 123nJ. The SA is developed by repeatedly dropping the WS 2 onto a fiber ferrule and a dried SA device is incorporated in the ring laser cavity. This technique offers simplicity in fabrication compared to composite film, besides it allows control over the insertion loss.In the experiment, we used a WS 2 pristine flakes solution, which was obtained by a liquid exfoliation method. The WS 2 flakes with the purity of more than 99% were dispersed by using a mixture of ethanol and water as a solvent. Then the dispersed solution was treated for 120min by a high-power ultrasonic cleaner. After sonication, the dispersion was allowed to settle for several hours. To remove large agglomeration, the dispersion was centrifuged at 3000 rpm for 30 min, after which the upper supernatant was collected. The concentration of WS 2 nanosheets i...