Switchable single/dual-wavelength Q-switched all-fiber laser utilizing thulium-doped fiber saturable absorber

A dual-wavelength Q-switched fiber laser is successfully demonstrated by utilizing an all-fiber configuration based on fiber saturable absorber (SA). An 18 cm-long Tm-doped fiber (TDF) is employed as a fiber SA since it presents an apparent nonlinear optical characteristic at near-infrared wavelength with 180 MW∕cm2 saturable intensity and 2% modulation depth. After splicing the TDF into an Erbium-doped fiber laser (EDFL) cavity, a stable dual-wavelength Q-switched pulses is generated with the aid of polarization controller as an optical wavelength selector. It operates at wavelengths of 1532.6 nm and 1557 nm (with wavelength spacing as wide as 24.4 nm). To the best of our knowledge, this is the dual-wavelength fiber laser with widest wavelength spacing reported so far. Furthermore, single-wavelength Q-switched operations of 1532 nm and 1558 nm are also realized, which can be flexibly switched between the two wavelengths just by merely manipulating the intra-cavity birefringence. The results attest that TDF SA combined with nonlinear polarization rotating technique can provide a simple and practical method for a switchable single/dual-wavelength all-fiber laser. The proposed all-fiber laser could be applied in terahertz communication, manufacturing, laser radar, and so on.