The optical absorption spectrum of ion-implanted silica is shown to become dichroic when it is photobleached with polarized 248-nm light. The dichroism is modeled by a photobleaching process that bleaches color centers preferentially depending on their local orientation with respect to the polarization of the photobleaching light. A similar photobleaching process may occur in photosensitive fiber, thus providing a possible explanation for the birefringence that is observed in the photoinduced index change.
Optics Letters
Department of Electronics

Albert, J, Malo, B., Johnson, D.C., Bilodeau, F., Hill, K.O., Brebner, J.L., & Kajrys, G. (1993). Dichroism in the absorption spectrum of photobleached ion-implanted silica. Optics Letters, 18(14), 1126–1128. doi:10.1364/OL.18.001126