  We investigate the collective dynamics of nonlinearly interacting modes in
multimode photonic settings with long-range couplings. To this end, we have
established a connection with the theory of spin networks. The emerging
"photonic spins" are complex, soft (their size is not fixed) and their dynamics
has two constants of motion. Our analysis shed light on the nature of the
thermal equilibrium states and reveals the existence of optical
phase-transitions which resemble a paramagnetic to a ferromagnetic and to a
spin-glass phase transitions occurring in spin networks. We show that, for
fixed average optical power, these transitions are driven by the type (constant
or random couplings) of the network connectivity and by the total energy of the
optical signal.
