In-fiber modal interferometer for high sensitivity gas detection

Abstract

We demonstrate a gas sensor based on mode interference in a hollow-core photonic bandgap fiber. Gas absorption of a pump laser beam induces phase modulation of a propagating probe beam, which is detected by use of an in-fiber modal interferometer. An estimated detection limit of ~2 ppm acetylene (~710 -5 in terms of noise equivalent absorbance or NEA) is achieved with 30-cm-long HC-PBF operating at the near infrared wavelength. This NEA is ~22 times better than state-of-the-art HC-PBF gas sensors based on direct absorption spectroscopy.

Hollow-Core Microstructured Optical Fiber Gas Sensors

“…The gaps between HC-PBF and the two FC/APCs are ~10 µm. These two FC/APCs are used at the launching and receiving ends to reduce Fabry-Perot interference due to reflections at the connecting joints and increase the excitation of cladding modes [92]. A DFB laser with wavelength at ~1530.37 nm was used as a pump laser and an ECDL with wavelength at 1556.58 nm was used as a probe laser.…”

“…Fig.14. Experimental setup for in-fiber MZI[92]. The fundamental mode of HC-PBF is used as sensing arm while the cladding modes of HC-PBF as reference arm.…”