An active core fiber optic gas sensing technique has been developed by using a photonic crystal (PC) hollow core fiber (HCF) as a transducer and a tunable diode laser as a light source for multi-gas sensing. The intrinsic optical absorption signal of an analyte molecule in the near infrared region is monitored for sensing C2H2, CO2 and NH 3. Although the overtone absorptions are known to have low absorption cross-sections, this sensor can detect these gas components down to the parts-per-million (ppm) level by using a 1-meter hollow core fiber as a transducer. The sensitivity of this gas sensing technique can be improved by introducing periodic openings along the fiber, decreasing the hole diameter down to 0.5 mm and using a longer hollow optical fibers. Other advantages of this gas sensing technique include less interference, fast response and potential applications like high temperature, remote and corrosive gas sensing.; Key words. absorption spectroscopy, laser diode, hollow core photonic crystal fiber.
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