Fabrication, characterization and mode locking application of single-walled carbon nanotube/polymer composite saturable absorbers

We present the fabrication of a high optical quality single-walled carbon nanotubes (SWNTs) polyvinyl alcohol (PVA) composite film. The composites demonstrate strong saturable absorption at ∼1.5 μm, the spectral range for optical communications. By measuring the nonlinear transmission of a sub-picosecond pump pulse through the film, we were able to deduce a saturation fluence of ∼13.9 μJ/cm² and a modulation depth ∼16.9% (in absorption) at a high pulse fluence ∼200 μJ/cm². Transient saturable absorption is investigated by measuring the transmitted autocorrelation traces at various incident power levels. Observed side-peak suppression indicates a fast recovery time on the scale of ∼1 ps for our saturable absorber devices. Furthermore, we use these SWNT-PVA composite saturable absorbers as mode-lockers in an Er³⁺ fiber ring laser and achieve ∼560 fs pulse generation with good jitter performance and long term stability. The laser performance is also associated with the parameters of our SWNT based saturable absorber.