Tungsten disulphide for ultrashort pulse generation in all-fiber lasers.

Tungsten disulphide (WS), which exhibits excellent saturable absorption properties, has attracted much attention in the applications of photonic devices. In this paper, WS is applied for the preparation of a saturable absorber (SA). Using the pulsed laser deposition (PLD) method, WS 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 WS SAs to improve their reliability and avoid oxidation and corrosion. Employing the balanced twin-detector method, the modulation depth of the fiber-taper WS SAs was measured to be 17.2%. With the fiber-taper WS 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 WS SAs with smaller waist diameter and longer fused zone are promising photonic devices for ultrashort pulse generation in all-fiber lasers.