Photoinduced second-harmonic generation in silica fibers doped with Er
3+, Sm3+, and Tb3+ has been investigated. Er3+-doped fibers have been
found to tune a chi(2) grating easily to the mode structure of the las
er radiation, whereas Sm3+-doped fibers have been found to possess the
greatest resiStance to chi(2) grating erasure by radiation at 532 nm.
From the beginning of the preparation processes, the third harmonic a
t 355 nm is registered in all the fibers.