Photothermal CO detection in a hollow-core negative curvature fiber

Abstract

We demonstrated the first photothermal CO sensor using a hollow-core negative curvature fiber (HC-NCF). The hollow-core fiber features a typical structure of one ring cladding containing eight nontouching capillaries to form a negative curvature core-surround. The photothermal effect in a 40-μm hollow core is induced by CO absorption at 2327 nm and detected by a Mach-Zehnder interferometer operating at 1533 nm. By using wavelength modulation spectroscopy, we achieved a normalized noise equivalent absorption (NNEA) coefficient of 4.4×10 -8 cm -1 WHz -1/2 . As CO has a very slow vibrational-translational (V-T) relaxation process, we enhanced the photothermal signal by enhancing the relaxation with the water vapor additive.

Modeling and performance evaluation of in-line Fabry-Perot photothermal gas sensors with hollow-core optical fibers

“…Different types of HCFs such as HC-PCFs and anti-resonant hollow-core fibers (AR-HCFs) may be used for PT gas detection [2,[4][5][6][7][8][9]. Understanding PT phase modulation dynamics in these fibers with varying structural parameters is important for the design of sensors with optimal performance.…”

“…To develop practical optical fiber PTI sensors with high sensitivity, various interferometric schemes, including Mach Zehnder interferometer (MZI) [2,4], Sagnac interferometer (SI) [5,6] and Fabry-Perot interferometer (FPI) [7], have been examined for the detection of the PT phase modulation. With a MZI configuration, short-term noise-equivalent gas (acetylene) concentration down to low parts-per-billion (ppb) level has been demonstrated with 1 to 10 meters of HC-PCFs [2,5,6].…”

Laser-Based Trace Gas Detection inside Hollow-Core Fibers: A Review

“…A gas filling time of 5 s was measured and a detection limit of only 0.4 ppm was obtained (30 s averaging). The same fiber was also used in [66], where carbon monoxide was detected with PTI. The system used in this paper is shown in Figure 12.…”

Oxygen Gas Sensing with Photothermal Spectroscopy in a Hollow-Core Negative Curvature Fiber

“…Compared to HC-PBFs, hollow-core negative curvature fibers (HC-NCFs) have simpler structures with an inverted curvature in the core wall [13], and much broader low-loss transmission windows [14]. With a HC-NCF capable of transmitting both near and mid infrared signals, detection of carbon monoxide down to ppm level has been demonstrated [15].…”