A hybrid mode-locked Erbium-doped fiber laser that provides very short pulse-widths while achieving high repetition rates is proposed and experimentally demonstrated. This hybrid configuration is realized by using a thin film of polydimethylsiloxane (PDMS) doped with single wall carbón nanotubes (SWCNT). This PDMS/SWCNT composite acts as a saturable absorber and is inserted within an active mode-locked laser system using angled connectors. Therefore, the effect of the PDMS/SWCNT composite is to effectively narrow the width of the pulses generated by the active system without modifying its repetition rate. A pulse-width of 730 fs was generated at a repetition rate of 4 GHz, while achieving an average output power of 4 mW. A reduction in the noise of the photodetected RF spectrum was also observed in the hybrid system.