Generation of bidirectional stretched pulses in a nanotube-mode-locked fiber laser

The bidirectional stretched pulses in a nanotube-based erbium-doped fiber laser are observed experimentally for the first time to our best knowledge. The proposed fiber laser generates two stable pulse trains in opposite directions with different central wavelengths, pulse widths, and repetition rates. In addition, the bidirectional operations with the same central wavelengths are also demonstrated by changing the polarization controller and pump power. Experimental results suggest that the cavity asymmetries together with the fiber birefringence play key roles in the formation of these unique features.