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 (Na2CO3) for producing an ultrafast mode-locked stretched pulse in a passively erbium-doped fiber laser at near-zero dispersion. The solid film of a Na2CO3-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/cm2. The mode-locking operation of the EDFL-based Na2CO3-SA was observed at a pump power of 117 mW. A stable stretched pulse was generated by using the proposed Na2CO3-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 Na2CO3-SA for generating a stretched-pulse mode-locked fiber laser.