Sodium carbonate modulated ultrashort mode-locked stretched pulses in an erbium-doped fiber laser

In this paper, we propose a new, to the best of our knowledge, saturable absorber (SA) based on sodium carbonate (Na 2 CO 3 ) for producing an ultrafast mode-locked stretched pulse in a passively erbium-doped fiber laser at near-zero dispersion. The solid film of a Na 2 CO 3 -SA was fabricated by the drop-casting method using polyvinyl alcohol as a host polymer. The modulation depth of the proposed SA, which was measured by a balanced twin detector technique, was 2.3% with saturation intensity of 181MW/cm 2 . The mode-locking operation of the EDFL-based Na 2 CO 3 -SA was observed at a pump power of 117 mW. A stable stretched pulse was generated by using the proposed Na 2 CO 3 -SA. The laser can generate pulses with a repetition rate and duration of 1.87 MHz and 820 fs, respectively, within a bandwidth of 6.6 nm. The single pulse energy reaches up to 5 nJ, which is equivalent to the average output power of 9.3 mW. Finally, to the best of our knowledge, this is the first report on using the Na 2 CO 3 -SA for generating a stretched-pulse mode-locked fiber laser.