Intermode beating mode-locking technique for a rare-earth-doped fiber pulsed laser

In this paper, we report the intermode beating mode-locking of a 2  μm Tm3+-doped fiber laser (TDFL) pumped by a 1565 nm continuous-wave multi-longitudinal-mode laser. Because strong intermode beating of the 1565 nm pump source induces the periodic modulation of 2 μm intracavity power, stable mode-locking of the TDFL is successfully established by precisely matching the 2 μm cavity frequency with the intermode-beating frequency of the 1565 nm pump source. The mode-locked laser, without requiring any specific mode-locking element, can stably emit the rectangular nanosecond pulses. The mode-locking operation at the center wavelength of 1980.35 nm has a >61  dB signal-to-noise ratio and a 34.496 MHz repetition rate. Although the preliminary results are not better than those of conventional mode-locking, intermode beating mode-locking in combination with rare-earth-doped fiber lasers could provide a promising and alternative solution for compact, low-cost, and high-performance pulsed laser sources.