The graphene-polymer SA thin film using solution blending method and atomic layer graphene as saturable absorber (SA) used to generate femtosecond laser pulse were measured. Stable soliton-like pulses with the pulsewidth of 403 fs and 432 fs, the spectral linewidth of 6.32 nm and 6.16 nm, and the time-bandwidth product of 0.315 and 0.329 using graphene-PVA film and atomic layer graphene as SA were achieved, respectively, in mode-locked Er-doped fiber ring laser. The graphene-PVA SA suffered from larger loss caused by graphene flake aggregating, while the atomic layer graphene had smaller nonsaturable loss which exhibited lower mode locking threshold power. Atomic layer graphene also had stable fabricated process and controllable modulation depth depended on its layer numbers. To compare the mode locking performance of single wall carbon nanotubes (SWCNTs) and graphene SA, the same solution blending fabricated sample was used. Under similar nonsaturable loss and modulation depth, the SWCNTs SA with optimized concentration of 0.5wt% and thickness of 188£gm had shortest pulsewidth of 440 fs and 3-dB spectral linewidth of 6 nm. The shortest pulsewidth of 403 fs and broad spectral linewidth of 6.32 nm was obtained using graphene SA with concentration of 6.25wt% and thickness of 18£gm. Graphene has broad band absorbance and larger modulation depth, the experimental result indicates that graphene SA can generate shorter pulse and has chance to become the potential candidate of SA.

The dependence of single-wall carbon nanotubes-based saturable absorber (SWCNTs SA) on concentration and thickness for mode-locked laser pulse formation is comprehensively investigated. The peak absorption wavelength of SWCNTs SA is engineered within the gain band-width of erbium-doped fiber centered near 1550 nm. The optima full-width half-maximum (FWHM) of pulses was obtained as the concentrations of SWCNTs SA was 0.05 wt%. This indicates that the laser pulse become shorter as the concentration of SWCNTs SA increases. The result also showed that the FWHM of pulses from 3.43 to 1.85 ps were found as the thickness of SWCNTs SA increased from 8 to 100 um. This also indicates that the laser pulse become shorter as the thickness of SWCNTs SA increases. However, the pulse width significantly broadened as concentration increased to 0.1 wt% and became stable as thickness of SWCNTs SA increased from 100 to 264 um for passively mode-locked lasers. An in-depth study on the optimum fabrication of concentration and thickness of SWCNTs SA for laser pulse formation may allow developing a cost-effective mode-locked laser with high performance as well as broadly benefit to the utilization of many other low-cost nanodevices.