Monitoring the Evaporation of Fluids from Fiber-Optic Micro-Cell Cavities

Abstract

Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identification of fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids.

Fluid evaporation monitoring with suspended-core fibers

“…Although with different geometries, one can verify the time dependency on length by comparing our ∼ 1.4 mm length fiber with the one from Preter et al, with a cavity length of 100 µm and a total evaporation time of ∼ 0.5 s for acetone. 6 During the study of evaporation dynamics, the sensing head was continuously interrogated using an OSA. The OSA's slow time response resulted in a small resolution of ±4 s. Still, as mentioned in the previous paragraph, the total evaporation time was an order of magnitude higher than this, which allows us to coarsely analyse the phenomenon spectrally.…”

“…5 Recently, Preter et al introduced a new technique in microstructured fibers for liquid sensing. 6 Using in-line microcavities etched in single-mode fibers, the authors proposed the monitoring of the evaporation dynamics of volatile organic compounds as a means to identify them. They tracked the evaporation of ethanol, hexane, acetone, and a mixture of ethanol and hexane, observing clear distinctions in light loss dynamics which effectively resulted in a volatile compound sensor.…”

Evaporation of fluids in suspended-core fibres

“…In particular, measurements of liquids have been performed either by effective refractive index changes in interferometric setups or by absorption spectrum analysis [4]. Recently, Preter et al introduced a new technique in microstructured fibres for liquid sensing [5]. Using in-line microcavities etched in single-mode fibres, the authors proposed the monitoring of the evaporation dynamics of volatile organic compounds as a means to identify them.…”

Open-Cavity Fabry-Perot Interferometer Based on Etched Side-Hole Fiber for Microfluidic Sensing

“…The selectivity stems from the different etching rate of different materials. Thus specially doped fibers are always employed, such as P 2 O 5 doped fibers [17]- [19], and B-doped polarization-maintaining fibers [20].…”