Multipoint side illuminated absorption based optical fiber sensor for relative humidity

Claudio Oliveira Egalon

doi:10.1117/12.2024875

25 September 2013 Multipoint side illuminated absorption based optical fiber sensor for relative humidity

Claudio Oliveira Egalon

Proceedings Volume 8847, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications VII; 88471H (2013) https://doi.org/10.1117/12.2024875
Event: SPIE Optical Engineering + Applications, 2013, San Diego, California, United States

Abstract

A side illuminated optical fiber sensor with three sensing points and an absorption-based indicator in the cladding was demonstrated for the first time. This device is easy to manufacture, uses leaky modes as the signal carrier and can measure RH in air, soil, concrete and other environments. So far, only side illuminated fluorescence sensors have been reported. They were thought, erroneously, to have their entire signal generated by evanescent wave coupling when, in fact, leaky modes also play an important role. This, coupled to the prevailing misconception that leaky modes propagate for very short lengths of fiber, prevented the earlier discovery of this absorption-based configuration. A 25 cm long fiber, with a cladding doped with an absorption dye sensitive to Relative Humidity (RH), was used in this demonstration. The fiber was side illuminated by a broadband LED, a fraction of this light was absorbed by the cladding and the remaining light guided to the fiber tip as low loss leaky modes. A total of three sensors, two with three sensing points and one with two, were calibrated using a low cost photometer. The signal was linear, stable, increased with RH and had resolutions between 0.11% and 0.25% in RH. With 5 mm diameter LEDs, devices with at least two sensing points per centimeter of fiber can be easily fabricated resulting in sensors with a very high density of sensing points. Compared to the prevailing axial illumination approach, the side illuminated sensor was found to be far simpler and inexpensive.

Citation Download Citation

Claudio Oliveira Egalon "Multipoint side illuminated absorption based optical fiber sensor for relative humidity", Proc. SPIE 8847, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications VII, 88471H (25 September 2013); https://doi.org/10.1117/12.2024875

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