A permanent index change of 0.0051% was induced in Sin 2/Sin 3doped aluminosilicate fiber by irradiating 2W of multi-line output from an Ar ion laser.The photosensitivty was detected by measuring a shift in LPll 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 Sin 2 ionabsorption bands enhanced by multiphoton Processes.