We have developed an industry-aimed pragmatic method based on a known model for the prediction of radiation induced losses in single mode optical fibers exposed to /sup 60/Co gamma rays. When environmental and measurement conditions are well defined, long-term losses could be predicted with a precision of about 15%, provided a sufficiently large data-set is available. From an interpretation of these results, we discuss its applicability and potential further improvements.

Optical fiber technology is seriously considered for communication and monitoring applications during the operation and maintenance of future thermonuclear fusion reactors. Their environment is characterized, in particular, by possibly high gamma dose-rates and total doses up to 100 MGy. The feasibility of applying photonic technique in such intense radiation fields therefore needs to be assessed. Whereas many reports deal with the radiation behavior of a variety of fiber-optic devices, only little information is available on the radiation tolerance at high total dose (e.g. > 1 MGy). We describe our recent results obtained at fiber-optic components intended for ITER (International thermonuclear Experimental Reactor) remote-handling applications. We have conducted high total dose (up to 15 MGy) irradiation experiments on a variety of COTS fiber- optic devices, including edge-emitting laser diodes, vertical-cavity surface-emitting lasers, PIN photodiodes and single-mode optical fibers. A remarkably low radiation induced loss was obtained on a single-mode pure silica core optical fiber, whereas VCSELs confirmed their excellent radiation hardness. With the exception of photodiodes, the optical characteristics of selected fiber-optic devices seem to be able to cope with high total gamma doses. However, our results also indicate that radiation induced degradation of connector assemblies might limit their use in severe radiation environments.

This paper presents the first results of long term experiments conducted within the SOFTI (Study of Optical Fibres and components under Thermal ageing and Irradiation) project. This on-going 6-years study is intended to determine the effects of ageing on the behaviour of optical fibres and their fibre-end components submitted to harsh environments, with respect to the safety of nuclear facilities. The test program consists of irradiations at low dose rates with different thermal constraints and spool radius. After completion, these tests will enable us to write a guideline for qualification procedures related to future fibre-optic systems, for their applications in nuclear facilities. The observations of these first results show a clear dependence of the radius of curvature for the radiation induced loss. To our knowledge, it is the first time that this was experimentally verified for a radius of curvature superior to 6 cm.

Up to now, fiber optics and several photonic components have been considered for space and nuclear power plant applications, mainly at relatively low dose rates and total doses. In this paper, we present our recent results of particularly high dose gamma irradiation tests performed with different fiber-optic components intended for applications in enhanced radiation environments such as ITER (International Thermonuclear Experimental Reactor), We present a radiation induced loss at 1310 nm as low as 30 dB/km, measured at a cumulated dose of 3 MGy for a pure-silica core single mode fiber. On-line measurements with commercially available vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm confirmed their excellent radiation hardness. Furthermore, we demonstrated that an initial power loss of about 6 dB is caused by an early degradation of a focusing lens in these connectorized components. A combined effect of dose rate, cumulated dose and temperature on the degradation of our devices under test (DUT) is evidenced

The basic components of fiberoptic links, such as light emitting diodes (LED), pin-type photodetectors (PD) and optical fibers are evaluated under (/sup 60/Co) /spl gamma/-ray irradiation, so as to ascertain their qualification for nuclear applications and to develop predictive models for their behavior under well defined environmental conditions, such as those encountered in nuclear power plants. This paper presents some results of irradiation tests, together with a discussion of proposals for optical fibers' behavioral models.