Experimental demonstration of phase bistability in a broad area optical   oscillator with injected signal
  We demonstrate experimentally that a broad area laser-like optical oscillator (a nondegenerate photorefractive oscillator) with structured injected signal displays two-phase patterns. The technique (G. J. de Valc\'arcel and K. Staliunas, Phys. Rev. Lett. (105), 054101 (2010)) consists in spatially modulating the injection, so that its phase alternates periodically between two opposite values, i.e. differing by pi 
R. Mart\'inez-Lorente, A. Esteban-Mart\'in, E. Rol\'an, K. Staliunas,   G. J. de Valc\'arcel, and F. Silva
physics.optics nlin.PS