We investigate the dynamical behavior of two laser diodes coupled through mutual injection of their optical fields when placed face to face with a small separation between them. We report symmetry breaking in periodic solutions at low coupling rates. In addition, we demonstrate that at higher coupling rates both lasers exhibit very fast periodic oscillations. The system is of practical interest, since it constitutes a tunable all-optical source of microwave oscillations. (C) 2003 Optical Society of America.