Photoinduced defect centers by harmonics of 1.06 micrometers photons in Ge-doped silica are discussed and proposed defect models reviewed in relation to the self-organization phenomena, such as Hill gratings and second harmonic generation (SHG) in Ge-doped silica core fibers. In particular, we will show that the reported preparation kinetics of SHG in both seeded and unseeded processes can be explained in terms of defect centers induced by the fourth harmonic of 1.06 micrometers photons. The SHG erasure kinetics can also be understood by the reaction of defect centers responsible for SHG with free excitons.