Tungsten disulphide for ultrashort pulse generation in all-fiber lasers

Tungsten disulphide (WS₂), which exhibits excellent saturable absorption properties, has attracted much attention in the applications of photonic devices. In this paper, WS₂ is applied for the preparation of a saturable absorber (SA). Using the pulsed laser deposition (PLD) method, WS₂ is deposited on the side surface of the tapered fiber. In order to obtain larger non-linearity of the SAs with evanescent wave interaction, the tapered fiber had a smaller waist diameter and longer fused zone. Gold film was deposited on the fiber-taper WS₂ SAs to improve their reliability and avoid oxidation and corrosion. Employing the balanced twin-detector method, the modulation depth of the fiber-taper WS₂ SAs was measured to be 17.2%. With the fiber-taper WS₂ SA, a generated pulse with 246 fs duration and a 57 nm bandwidth was obtained at 1561 nm. The electrical signal to noise ratio was better than 92 dB. To our knowledge, the pulse duration was the shortest among the reported all-fiber lasers with transition metal dichalcogenide (TMD) SAs. These results indicate that fiber-taper WS₂ SAs with smaller waist diameter and longer fused zone are promising photonic devices for ultrashort pulse generation in all-fiber lasers.