Synchronization of Mutually Coupled Self-Mixing Modulated Lasers

Synchronization of mutually coupled chaotic lasers has been demonstrated in a microchip ${\mathrm{LiNdP}}_{4}{\mathrm{O}}_{12}$ laser array with self-mixing feedback modulation. An abrupt transition to synchronized chaos by way of ``phase squeezing'' was observed when coupling between the two lasers was increased. This phenomenon is well reproduced by numerical calculations using model equations. It is also shown that low energy variation as well as high disorder are concurrently established in synchronized chaos.