Mid-infrared refractometer based on side-polished indium fluoride fiber for monitoring relative humidity

Abstract This work developed a fiber-optic refractometer taking advantage of the anomalous dispersion by water as an approach to monitoring relative humidity. The sensor part of this device was fabricated by mechanical polishing of an indium fluoride fiber capable of transmitting mid-infrared radiation. This sensor was found to respond to variations in relative humidity as a consequence of rapid changes in the external refractive index related to the condensation of water on the exposed fiber. Clear signal variations were also obtained in response to exposure to human breath when using a sampling rate of 10 Hz.