Photoinduced second-harmonic generation and luminescence of defects in Ge-doped silica fibers

We have measured the efficiency of photoinduced second-harmonic generation (SHG) in Ge- doped silica fibers containing different concentrations of 'GeO' and 'GeH' defects. The relative concentration of these defects were varied by heat treatments in H2 and determined using luminescence spectroscopy. The results show that the GeH defect center, which can be excited in the visible (around 500 nm) and luminescence around 700 nm, plays a role in the photoinduced SHG process. On the other hand, the results do not allow us to rule out contributions from the GeO defects.