  We reported on the generation of femtosecond pulse in an anomalous-dispersion
fiber ring laser by using a polyvinyl alcohol (PVA)-based Topological Insulator
(TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable
optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By
incorporating the fabricated PVA-TISA into a fiber laser, mode-locking
operation could be achieved at a low pump threshold of 25 mW. After an
optimization of the cavity parameters, optical pulse with ~660 fs centered at
1557.5 nm wavelength had been generated. The experimental results demonstrate
that the PVA could be an excellent host material for fabricating
high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a
good candidate for ultrafast saturable absorption device.

Optics