A permanent index change of 0. 005 1% was induced in Sm+2/Sm+3 doped aluminosilicate fiber by irradiating 2 W of multi-line output from an Ar ion laser. The photosensitivity was detected by measuring a shift in LPn mode cutoff wavelength. Bleaching of a broad absorption band in the visible was also observed. The origin of the photosensitivity in the Sm doped optical fiber is the bleaching of Sm+2 ion absorption bands enhanced by multiphoton processes.