Circling Vortices and Pattern Dynamics in aUnidirectional Photorefractive Ring Oscillator

We report results on unidirectional oscillation in a photorefractive oscillatorimplemented with BaTiO3 that is actively stabilized. Dynamic spatial patterns andpattern competition were observed, depending strongly on the Fresnel number of the system. Asthe origin for spontaneous pattern alternation we identified variations in the cavity length that arein turn mainly due to temperature fluctuations. By varying the cavity length, we were able toadjust stable patterns of different mode families and control pattern dynamics as mode beats,optical vortices and their rotations and more complex pattern dynamics for higher Fresnelnumbers.