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IRG-I Nugget

Optical fibers that can take their own temperature

Left panels : Power dissipation along a bent fiber; Top : Photograph of a bent fiber captured by an IR camera for a dissipated power of 700 mW; Bottom : The temperature distribution along the fiber. Right panels : Power dissipation at a localized defect in a fiber; Top : Photographs of a fiber containing a single localized defect (upper section) and a defect-free fiber (lower section) captured by an IR camera. Both fibers carry identical CO 2 laser energy. High power IR light accumulates at the defect site, and consequently heats up the region around the defect; Bottom : Temperature distributions along the two fibers shown above.

Members of IRG-I of the MIT MRSEC have recently succeeded in developing fully integrated optical fibers that are capable of monitoring their own temperature and, as a result, detecting defects that could result in failure of a high power optical transmission line (Bayindir, et al., Nature Materials 4 , 820-825, 2005). This is a very important advance demonstrating for the first time the ability to integrate optical, electrical and thermal devices within a single fiber structure. The fibers comprise an optical transmission element which is a hollow-core multilayer cylindrical photonic band gap structure designed for the transport of high power radiation with multiple thermal-detection elements, made of metal-semiconductor-metal junctions located in the vicinity of the hollow core for the purpose of distributed temperature monitoring. Metal electrodes extend along the length of the fiber in contact with the thermal-detecting elements to deliver an electrical response to the fiber ends. The temperature dependence of the electrical conductivity of the semiconductor material allows for the discrimination - in real time - between normal transmission conditions and those which are typical of localized defect formation, thus enabling for the first time a self-monitoring high power optical transmission line for failure prediction and prevention. The ability to integrate optical transport and thermal monitoring for failure prediction is of paramount importance if high power optical transmission lines are to be operated safely and reliably in medical, industrial and defense applications. This work may also pave the way for new types of fiber sensor devices.

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