Radiation-resistant WDM optical link for thermonuclear fusion reactor instrumentation

The future International Thermonuclear Experimental Reactor (ITER) is a com plex installation that will require permanent monitoring and frequent maint enance operations. The high-gamma dose rates, the high neutron fluence, and other radiological hazards call for the use of remote-handled equipment. T he management of heavy umbilicals connecting the control systems with the r emote tools is therefore a key issue. Multiplexing signals can relieve the cable-handling difficulties. In this respect, the intrinsic wavelength divi sion multiplexing (WDM) capabilities of fiber-optic technology make it a ve ry promising candidate for integration in ITER instrumentation links. Howev er, the radiation hardness of a complete WDM optical link still needs to be assessed. In this paper, as a first step toward the development of a rad-h ard WDM optical link, we report on irradiations of different parts of a typ ical WDM optical link. We present our irradiation results on COTS fiber-opt ic devices, including WDM single-mode couplers, which remain operational up to MGy dose levels while the channel drift observed in narrow-band coupler s compromises their use in WDM multiplexers. The intrinsic wavelength encod ing of fiber Bragg grating (FBG) sensors makes them ideal candidates for WD M fiber-optic sensor networks. Therefore, we also investigated the gamma -r adiation response of FBGs written in germanosilicate fibers. We irradiated such sensors up to MGy dose levels. At a total dose of 0.1 MGy, saturation of the radiation-induced Bragg peak shift has been observed, evidencing the potential radiation hardness of FBG-based devices in highly radioactive en vironments. To illustrate wavelength multiplexing in sensing, we discuss ou r preliminary results on a new multicomponent force sensor design based on eight multiplexed FBG sensors intended for use at the end effector wrist of remote-controlled robots. Finally, we present the in-reactor irradiation r esults of standard Corning Ge-doped fiber up to GGy dose levels.