Radiation testing of fiber optic systems

Tests have been performed to examine the effects of radiation exposure on opto-electronic components that can be used in digital fiber optic data links. The response of fiber waveguides to ionizing radiation has been studied. Measurements of the growth and decay of the radiation-induced loss at 850 and 1300 nm have revealed that fibers are very sensitive to low γ-doses (2000 rad). The linear dependence of a short circuit current on a γ-dose rate, up to 380 rad/s for the photodiode has been shown. At very high dose levels permanent damage is noticed in the diode characteristics and its current decreases where a value of 1600 μA, measured at light intensity level of 8000 1x, was reduced to 1200, 950, 820, 700, 600 and 550 μA after γ-exposure up to 2.0, 16, 38, 70, 105 and 140 M rad respectively. The forward current gain factor of a phototransistor, measured as a function of operating collector current, shows a severe decrease due to γ-exposure. The minimum damage effects, usually correspond to the lower and higher ends of the operating collector current range of a device. Proposals using photodiodes for γ-dose and dose rate-dosimetry are given, tested and proved to be satisfactory.