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  • Integrated Fiber Monitors Itself for Thermal Leakage

Photonics Spectra
Jan 2006
Anne L. Fischer

If there are failures in the high-power fiber optic lines used in medical, industrial and defense applications, the problems can be huge. It is, therefore, important to be able to predict and prevent such failures.

Researchers at Massachusetts Institute of Technology in Cambridge have developed a fiber with an embedded device that integrates optical, electrical and thermal elements for monitoring optical transport. The fiber is made up of a polymer insulator, a large-bandgap semiconductor, a narrow-bandgap semiconductor and metallic elements. The fiber transmission element guides 10.6-µm radiation along the fiber axis in a hollow core lined with a photonic bandgap structure.

Integrated Fiber Monitors Itself for Thermal Leakage
An integrated fiber can transmit a high-power laser beam in the hollow core while simultaneously monitoring the temperature along the fiber and delivering an electrical signal.

Multiple thermal detection elements are placed near the hollow core to monitor the temperature along the full length of the fiber. Each element comprises a metal/semiconductor/metal device, with both metal electrodes extending uniformly along the fiber.

One of the greatest challenges in the development of this integrated fiber, said lead researcher Mehmet Bayindir, was to find four different, yet compatible, materials that could be drawn together into a single fiber.

To test the design, the scientists delivered high-power CO2 laser radiation through the fibers, measuring the current through the metal/semiconductor/metal junctions at the periphery. In normal operation, some power dissipation occurred in the fiber, resulting in a low current flowing through the metal electrodes. The formation of a localized defect at any point, however, triggered a dramatic increase in the current caused by the change of the semiconductor’s electrical conductivity. The existence of defects was independently corroborated through the use of an IR camera. Bayindir indicated that integrating fault monitoring into optical fiber lines could help ensure safety in high-power optical transmission lines in critical applications. The next step is to explore different fiber sensor devices, including a fabric that is sensitive to temperature.

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