Gas Sensing System Based on an All-Fiber Photothermal Microcell

Abstract

This paper presents an all-fiber, miniature Fabry-Perot gas sensor based on photothermal absorption spectroscopy with a custommade and cost-efficient interrogation system. The sensing gas microcell has a diameter of 125 μm, a length of 1 mm, and allows for free gas exchange within the optical resonator through micromachined slits. High light intensity and confinement is ensured by delivering the excitation light directly into the gas microcell through a lead-in singlemode fiber. This enhances the photothermal effect and provides a short system response time. The interrogation system utilizes the modulation of an excitation laser diode with a fixed frequency while locking the probe laser onto the gas microcell's quadrature point and observing the variations of the reflected optical power. To show the potential of the proposed system, nitrogen dioxide was measured in dry air. Thereby, a limit of detection of 20 ppm could be achieved for 10 seconds` integration time. Furthermore, the small dimensions of the sensor allow for improved dynamic performance with photothermal modulation frequencies as high as 7 kHz.

Micro-Ring Resonator Assisted Photothermal Spectroscopy of Water Vapor

“…Recently, Krzempek et al have used miniaturized fibre-based Fabry Perot cavity sensors to retrieve the PTS signal in a proof-of-concept measurement of methane [ 12 ]. Similarly, Njegovec et al have demonstrated an all-fibre PTS gas sensor, comprising a probe fibre, a slotted capillary and an excitation fibre [ 13 ], and Yao et. al.…”