Dissolved gas sensing using an anti-resonant hollow core optical fiber
Jason Kapit, Anna P. M. Michel
Abstract
Sensors that measure dissolved gases directly are needed for environmental, industrial, and biomedical applications. Here we present a hollow core fiber optic sensor capable of measuring dissolved methane gas in liquids using only nanoliters of sample gas. The sensor is based on an anti-resonant hollow core fiber combined with a permeable capillary membrane inlet that extracts gas from the liquid for analysis. Using a small capillary inlet for gas extraction is only possible due to the small amount of sample gas needed for analysis, and it presents new possibilities for dissolved gas analysis in a simple, robust, and compact sensor configuration. We demonstrate the sensing technique using wavelength modulation spectroscopy and measure methane dissolved in water with a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>1</mml:mn> </mml:mrow> <mml:mi>σ</mml:mi> </mml:math> lower detection limit of 230 ppb, a resolution of 45 ppb, and a response time of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>8</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo movablelimits="true" form="prefix">min</mml:mo> </mml:mrow> </mml:math> .