Synchronization of noisy delayed feedback systems with delayed coupling

Synchronization of delayed coupled and stochastically perturbed systems with delayed nonlinear feedback is studied, using as an example circular chains of three and four delayed coupled Ikeda oscillators. It is proved that in the case of multiplicative noise the exact synchronization in the mean occurs for sufficiently large coupling, and an analytic estimate of the sufficient coupling is given. The sufficiency condition is compared with numerical computations, and typical effects of noise on the exact and some generalized types of synchronization are illustrated.