Radiation sensitivity of fibre optic couplers

In order to estimate the radiation sensitivity of a data transmission system based on optical fibres, the radiation induced loss of other included passive components has to be known, too. We have irradiated (at room temperature) a variety of couplers made by different manufacturers at a 60Co source with a dose rate of 1300 rad (SiO2)/min up to a total dose of 10 exp 6 rad (SiO2). Most of them were fabricated by the Fused Biconical Taper process of 200/280 micrometer multimode step index fibres (tested at lambda about 850 nm), and of 10/125 micrometer single mode fibres (tested at lambda about 1300 nm and lambda about 1550 nm). Couplers with 50/125 micrometer gradient index fibres (tested at lambda about 850 nm and lambda about 1300 nm) were also among them. The measured coupler inherent losses were between about 0.01 dB (fused coupler, high OH MM step index fibres, lambda=865 nm) and about 50 dB (coupler made of GRIN lenses, lambda=865 nm).