Nucleation of wave defects and formation of optical localized structures in bi-directional ring lasers

We show that class A bi-directional ring lasers do not support the existence of cavity solitons even under the presence of diffusion for the electromagnetic field. However there is a parameter range where an infinite number of patterns coexist. Such coexistence yields optical localized structures whose dynamical properties are in many ways similar to those of cavity solitons. In particular they allow writing and erasing under the action of very specific perturbations