Microstructured optical fibers for fluid sensing applications

TLDR: In this paper, a five-hole caterpillar-like microstructured optical fiber (MOF) was designed and post-processed using focused ion beam in order to create microfluidic channels to the external environment that would allow fluids to flow in and out of the fiber even after being spliced on both ends.

Abstract: Optical fiber sensors are one of today’s most prominent research fields in the optical fibers’s domain. This area has been greatly stimulated by the appearance of Microstructured Optical Fibers (MOFs) which allow the structural tailoring of fibers at a very small scale. In particular, MOFs with holes that allow the interaction of fluids with light hold promises in new detection configurations. The present dissertation addresses the fabrication, post-processing and application of MOFs in fluid sensing. After a brief review on chemical optical fiber sensing, the design and fabrication of a five-hole caterpillar-like MOF through a stack-and-draw procedure is described, envisaging future applications in fluid sensing. This fiber was subsequently post-processed using a Focused Ion Beam in order to create microfluidic channels to the external environment that would allow fluids to flow in and out of the fiber even after being spliced on both ends. Afterwards, a suspended-core fiber was fusion spliced to a single-mode fiber and a new sensing configuration was proposed for the detection of volatile organic compounds. By allowing these substances to fill the fiber’s holes in the liquid phase through capillarity forces and then tracking their evaporation dynamics, it was possible to distinguish the behaviour of acetone and isopropyl alcohol, paving the way to a new class of sensors based on evaporation monitoring. Finally, proposals on future developments based on what was achieved with this dissertation are mentioned, evidencing the potential that this work may have in the area of optical fiber sensing.