Two-photon-resonant photoinduced second-harmonic generation in Er 3+ -doped germano-aluminosilicate optical fibers pumped at 1.319 μm

The growth of a two-photon-resonant photoinduced second-harmonic signal at 660 nm in Er3+-dopect GeO2–Al2O3–SiO2 single-mode optical fibers pumped by a Nd:YAG laser at 1.319 μm is reported. Defect states in the band gap are optically excited through a resonant two-photon absorption process connecting the 4I15/2–4F9/2 energy levels of the erbium ions present in the fiber core. As a result a periodic χ(2)grating is formed, and efficient second-harmonic generation takes place. For erbium-free GeO2-doped silica test fibers no second-harmonic signal has been detected, even after hours of seeded preparation process.