Mode-lock, Q-switch and CW operation of an Yb-doped double-clad fiber ringlaser

We investigate the dynamics of a high power unidirectional Yb-doped fiber r ing laser with an intracavity polarizer placed between two halfwave plates. We show that, depending on the respective orientation of the phase plates, the laser operates in different regimes: CW, Q-switched, mode locked, or u nstable. The passive method exposed here allows us to choose the operating regime of the laser by a simple rotation of a halfwave plate. (C) 2001 Else vier Science B.V. All rights reserved.