Experimental observation of linear and nonlinear optical Bloch oscillations

We experimentally demonstrate the occurrence of optical Bloch oscillations in a waveguide array with linearly growing effective index of the individua l guides. We monitored the output profiles for varying propagation lengths and observed a periodic transverse motion of the fold and a complete recove ry of the initial excitation. The action of the focusing nonlinearity leads to a loss of recovery, symmetry breaking, and power-induced beam spreading .