High-energy square-wave pulses generated in a 1/1.5-µm dual-band mode-locked fiber laser

The generation of square-wave pulses in a 1/1.5-µm dual-band mode-locked fiber laser is experimentally demonstrated. The laser is based upon a peculiar "figure-θ" architecture that exploits a single active fiber to realize dual-band operation. High-energy square-wave pulses are simultaneously generated in both the 1-µm and the 1.5-µm spectral band using the laser. The 1-µm pulse maintains wave-breaking-free operation during the increase of the pump power and finally achieves energy as high as 88.6 nJ, while the 1.5-µm pulse achieves energy up to 1.5 µJ before it ultimately collapses into second-order mode locking. To the best of our knowledge, this is the first report on the formation of square-wave pulses in dual-band mode-locked fiber lasers.