Ammonia Gas Sensor Based on Graphene Oxide-Coated Mach-Zehnder Interferometer with Hybrid Fiber Structure

Abstract

A graphene oxide-coated in-fiber Mach-Zehnder interferometer (MZI) formed with a multimode fiber-thin core fiber-multimode fiber (MMF-TCF-MMF) is proposed and experimentally demonstrated for ammonia gas (NH3) sensing. The MZI structure is composed of two segments of MMF of length 2 mm, with a flame-tapered TCF between them as the sensing arm. The MMFs act as mode couplers to split and recombine light owing to the core diameter mismatch with the other fibers. A tapered TCF is formed by the flame melting taper method, resulting in evanescent wave leakage. A layer of graphene oxide (GO) is applied to the tapered region of the TCF to achieve gas adsorption. The sensor operates on the principle of changing the effective refractive index of the cladding mode of a fiber through changing the conductivity of the GO coating by adsorbed NH3 molecules, which gives rise to a phase shift and shows as the resonant dip shifts in the transmission spectrum. So the concentration of the ammonia gas can be obtained by measuring the dip shift. A wavelength-shift sensitivity of 4.97 pm/ppm with a linear fit coefficient of 98.9% is achieved for ammonia gas concentrations in the range of 0 to 151 ppm. In addition, we performed a repetitive dynamic response test on the sensor by charging/releasing NH3 at concentration of 200 ppm and a relative humidity test in a relative humidity range of 35% to 70%, which demonstrates the reusability and stability of the sensor.

Polyacrylic Acid/Polyaniline-Coated Multimode Interferometer for Ammonia Detection

“…The Fe 2 O 3 -coated tapered microfiber interferometer (MFI) [ 14 ] has a very wide detection range, but its sensitivity is correspondingly low. The GO-coated MZI sensor [ 15 ] also presents a wide detection range; however, its response time is too long to limit its practical application. The graphene-coated MZI sensor [ 17 ] is made of a pair of 3 dB LPFGs, which achieved good response in the NH 3 concentration range of 10–180 ppm, while its response time is also long, and its fabrication is very complex.…”

“…The Fe 2 O 3 nanotubes were used as the sensitive layer to enhance the adsorption of NH 3 molecules and the intensity distribution of the evanescent field of the sensor, achieving an extreme range of NH 3 detection. Fan et al [ 15 ] proposed an NH 3 sensor based on the Mach–Zehnder interferometer (MZI). A linear response to NH 3 in the range of 0–151 ppm was achieved by coating the sensor surface with graphene oxide (GO).…”

“…are also changed. Currently, various materials have been applied for ammonia sensing, such as graphene oxide (GO) [ 15 ], graphene [ 17 ], metal oxides [ 18 ], PAni, etc. GO has a large specific surface area and good gas adsorption properties.…”

Multimode interference self-imaging optical fiber sensor based on sol-gel silica for methane detection

“…In addition, incorporation of sol-gel silica which exhibit porous structures can attribute to better adsorption of analyte molecules. Due to the presence of multiple functional groups such as Si-O-Si and Si-OH, the realization of sol-gel silica is ideal solution to capture the small molecules such as CH 4 by forming the surface hydrogen bonds [15]. As the methane molecules present, the adsorption of methane with the silica nanostructure at the cladding-air interface took place via physisorption which subsequently affect the hole concentration of silica.…”

Induced Birefringence by Drop Cast in EFBG Ammonia Sensors

“…Therefore, PDIs are promising materials for the development of optical sensors for ammonia detection. In recent years, several authors presented high sensitivity ammonia sensors based on functionalized optical fibers applied to detect ammonia in gas phase and liquid solution [12][13][14][15][16][17] A recent review of fiber optic sensors for gases, vapors and ions can be found at [18]. Fiber Bragg gratings are a class of optical sensors that have attracted attention of researchers in recent decades due to properties such as wavelength coding, multipoint remote sensing, electrical passivity and electromagnetic immunity.…”