Stochastic holey optical fibers for gas sensing applications

Monitoring of gaseous species is important in a variety of applications including industrial process gas monitoring, mine safety, and homeland security. Fiber optic sensors have been used in a variety of forms to monitor various types of gaseous species. Optical fiber sensors utilizing both random hole and photonic crystal fibers have been investigated. One limitation to these types of fiber sensors is the fact that the holes run parallel to the optic axis of the fiber, requiring gases to diffuse over long distances. Diffusion of gases over long distances through tube sizes which are on the order of microns is a relatively slow process. This can significantly impact the response time of the sensors which are made from these types of fibers. This paper presents results on the development of optical fibers for gas sensing applications which have holes extending in the radial direction as opposed to the longitudinal direction (as in the case of photonic crystal fibers). The holes are made by a process which utilizes phase separation of the glass matrix at relatively low temperatures. The secondary phase is removed by subsequent leaching processes, leaving a three dimensionally porous structure. The porosity is arranged in a stochastic fashion within the fiber. Results of the fiber sensor development and testing will be presented. The microstructural analysis of the fibers by scanning electron microscopy as well as the optical characterization of the fibers will be presented. Fabrication procedures for the optical fibers and the optical fiber sensors will also be described.

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