The long-term behaviour of erbium-doped fibres under gamma-ray irradia
tion at a low dow rate of 0.5R/year was predicted for the purpose of a
pplying the fibres to transoceanic transmission systems, based on the
experimental result that permanent defects in fibres were dominantly g
enerated at low dose rates. The estimated degradation of transmission
loss and amplification gain after 25 years in undersea were 0.04dB/km
and 0.3dB, respectively.