Comparison of mode-locking regimes in a holmium fibre laser

A comparison has been performed for two mode-locking regimes in an all-fibre holmium laser: locking due to nonlinear polarisation rotation (NPR) and hybrid mode-locking (NPR with application of single-walled carbon nanotubes). The characteristics of pulsed lasing in both regimes are investigated. Pulsed lasing is obtained at wavelengths of 2072 and 2082 nm, with FWHM values of 3.7 and 3.3 nm, respectively. The pulse width in both cases does not exceed 1.5 ps. The pulse energies in the NPR mode-locking and hybrid mode-locking regimes are 0.4 and 0.3 nJ, respectively. It is shown that the signal-to-noise ratio in the case of hybrid modelocking is 3 dB better than that implemented under conditions of NPR mode-locking. A possibility of self-starting a laser system by applying hybrid mode-locking is indicated.