Abstract
In this work, we propose an interferometric humidity sensor based on a polymer micro-cap bonded off-center on the polished end of a standard single mode fiber (SMF). In our sensor, the sensitive part is the micro-cap. In the interferometer fabrication process, we can adjust the misalignment between the core and the micro-cap. It allowed us to control the visibility of the interference pattern. In our device, water molecules absorbed by the polymer microcap causes changes in the height of the microcap. This results in measurable shifts of the interference pattern. The fabricated samples were tested in a calibrated climatic chamber in the range from ˜10 to ˜95% of relative humidity (RH). The sensitivity and resolution of our device was found to be 148 pm per %RH and 0.04% RH, respectively. The obtained results suggest that our sensors can be useful to monitor relative humidity (RH) in miniature spaces.
Highlights
Humidity measurements have relevant importance in many areas of applications including, for example, manufacturing processes, [1] breath monitoring [2,3,4,5], or meteorological studies [6]
The polymer that we used to fabricate the micro caps onto the single mode fiber (SMF) can absorb water molecules [59]
Such polymer swells when it is exposed to relative humidity (RH)
Summary
Humidity measurements have relevant importance in many areas of applications including, for example, manufacturing processes, [1] breath monitoring [2,3,4,5], or meteorological studies [6]. Fabry-Perot (FP) cavities are good alternatives to monitor humidity In this case, a thin layer of hygroscopic material is deposited on the end face of an optical fiber [44,45,46,47]. A thin layer of hygroscopic material is deposited on the end face of an optical fiber [44,45,46,47] The advantage of this type of humidity sensors is their miniature size. Despite the many advantages that humidity sensors based on optical fibers have, their characteristics must be improved to compete with their electronic sensors counterpart These characteristic include simpler design and reproducible fabrication methods which may lead to lower sensor costs. An additional advantage of our humidity sensors is their microscopic dimensions
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