Response of germanium-doped fiber Bragg gratings in radiation environments

Fiber Bragg gratings were examined in situ while exposed to gamma-ray and proton environments that emulated or exceeded nominal low earth orbit radiation doses. Radiation and temperature induced changes to the reflected Bragg grating amplitude and spectral characteristics were observed in fiber gratings not formed under hydrogen loading. THe irradiations were performed in situ, while the ambient temperature near the Bragg grating was allowed to vary. Shifts in the reflected spectra from the Bragg gratings were observed and attributed to ionization and thermal effects. During irradiation, the spectral shifts were observed to move to longer wavelengths, saturate at low dose and to decrease exponentially following the cessation of radiation.