Self-stabilization of synchronously mode-locked lasers

An empty and highly attenuating external cavity was recently shown to have a powerful stabilizing influence on a synchronously mode-locked laser. Numerical simulations presented here demonstrate how this stabilization technique works. For an external cavity marginally shorter than the main cavity, the extremely weak reinjected signal isolates the mode-locked pulse from the noise background, which otherwise causes jitter. The new technique is likely to be of considerable importance for researchers using this popular type of mode-locked laser.