We derive rigorous conditions for the synchronization of all-optically
coupled lasers. In particular, we elucidate the role of the optical coupling
phases for synchronizability by systematically discussing all possible network
motifs containing two lasers with delayed coupling and feedback. Hereby we
explain previous experimental findings. Further, we study larger networks and
elaborate optimal conditions for chaos synchronization. We show that the
relative phases between lasers can be used to optimize the effective coupling
matrix.Comment: 21 pages, 10 figure
