Generation of 12th order harmonic mode-locking in a Nd-doped single-mode all-fiber laser operating at 0.9 µm

Based on the Nd-doped single-mode fiber as the gain medium, an all-fiber 12th harmonic mode-locked (HML) laser operating at the 0.9 μ m waveband was obtained for the first time, to the best of our knowledge. A mandrel with a diameter of 10 mm was employed to introduce bending losses to suppress mode competition at 1.06 μ m, which resulted in a suppression ratio of up to 54 dB. The 1st – 12th order HML pulses with the tunable repetition rate of 494.62 kHz – 5.94 MHz were obtained in the mode-locked laser with a center wavelength of ∼ 904 nm. In addition, the laser has an extremely low threshold pump power of 88 mW. To the best of our knowledge, this is the first time that an HML pulse has been achieved in a 0.9 μ m Nd-doped single-mode all-fiber mode-locked laser with the advantages of low cost, simple structure, and compactness, which could be an ideal light source for two-photon microscopy.