An Analysis of Photobleaching Techniques for the Radiation Hardening of Fiber Optic Data Links

The effects of light signals propagating within a fiber optic waveguide on the magnitude, spectral character and stability of radiation-induced optical absorption have been investigated. In particular, the prospects for the utilization of photobleaching techniques to increase the radiation hardness of fiber optic links has been assessed for typical state-of-the-art optical fibers. Both steady state and pulsed light sources have been employed. Fibers fabricated both from high purity synthetic silica and selectively doped silicas have been utilized. The nature of the photo-bleaching process in silica-based glasses is discussed and the characteristics of the photoluminescence accompanying the bleaching process are reported. It is concluded that the selective use of optical bleaching in irradiated fiber optic waveguides provides a useful method for increasing the operational hardness of a data link. This can be accomplished at modest power levels achievable with present day solid state light sources, and the system can be configured such that the transmitted and bleach signals are identical. The technique is most effective in pure silica core materials and promises to primarily impact systems with modest length requirements in which high light intensities can be launched throughout the link. Second generation waveguides with lower intrinsic losses will make the photobleaching approach useful even for extended ranges. The possibility of self-photobleaching waveguides containing luminescent ions is also discussed.