The influence of 1064-nm light on x(2) gratings at 790/395 nm in Tm-doped fibers

Abstract

We have investigated the influence of Nd: YAG laser light at 1064 nm on the growth and erasure of x (2) gratings using 790/ 395-nm light in Tm-doped fibers. The addition of 1064-nm light to the writing pair of 790/395 nm was observed to cause at most a slight increase in writing speed in a low-Tm (4 ppm) fiber; Nd: YAG irradiation was furthermore observed not to erase a previously written 790/395-nm grating. In a high-Tm (600 ppm) fiber, however, the growth rate of a 790/395-nm grating decreased substantially when 1064-nm light was added during writing. Also, exposure of a previously written grating at 790/395 nm to 1064-nm light caused a rapid drop in second-harmonic generation (SHG). These observations are determined to result from Nd: YAG-induced photodarkening, which can be partially reversed by prolonged exposure to 790-nm light. These results imply either that intense Nd: YAG irradiation does not produce mobile electrons or that the mechanism of second-harmonic generation in these fibers does not involve static macroscopic electric fields.