In situ measurement of refractive index changes induced by gamma radiation in germanosilicate fibers

We propose a technique to measure in situ the refractive index changes induced by ionizing radiation in single-mode optical fibers. This change can be derived from the channel drift appearing in narrow channel wavelength-divisionmultiplexing couplers exposed to gamma radiation. We measured a radiation-induced refractive index change of about 5 10/sup -6//kGy[H/sub 2/O] at low doses and 5 10/sup -7//kGy[H/sub 2/O] at higher doses. No saturation was observed up to a total gamma dose of 13 MGy.