Abstract

The χ⁽²⁾ grating that is induced by intense infrared pulses in GeO₂-doped silica fibers has previously been shown to be erasable by green light.¹,² Here we report the erasure of the χ⁽²⁾ grating by prolonged exposure to infrared light only. We used two kinds of small- core GeO₂-doped silica fibers: fibers A and B have GeO₂ contents of 19 mol% and 4 mol%, respectively. The fibers were seeded with 1064 nm light and its second harmonic (SH) 532 nm light by using a mode-locked and Q-switched Nd:YAG laser. The SH conversion efficiencies of the seeded fibers were similar (of order 10⁻³), despite the quite different GeO₂ concentrations. Although the SH power of fiber A decreased with time while reading with the 1064 nm light only, such a decay was not observed in fiber B, even at the same 1064 nm intensity. Moreover, the decay rate of the SH power in fiber A increased with increasing 1064 nm reading power. It was found that the decay rate is proportional to the 4th power of the 1064 nm power. This suggests that the decay of the χ⁽²⁾ grating is due to the two-photon absorption of the generated SH light, which is caused by Ge-related defects.

© 1990 Optical Society of America