‘Lab around fiber’ humidity-enhanced ammonia sensor: Multimode interference functionalized by graphene oxide

Abstract

In the paper, a fiber-optic ammonia sensor based on a no-core fiber (NCF)-type multimode interferometer is proposed. This sensor can utilize high humidity to enhance the sensitivity for ammonia detection. It is easily constructed by fusion splicing single-mode fiber (SMF)-NCF-SMF structure. The NCF is tapered to improve sensitivity for surrounding refractive index. To impart ammonia sensing capability to the structure, the interferometer is coated alternately with graphene oxide (GO)/ polyethyleneimine (PEI) composite films using the layer-by-layer method (LbL). The surface morphology and composition of the GO/PEI composite films are characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The ammonia sensing performance is tested, and the experimental results indicate that the central wavelength has obvious response of ammonia concentrations changing. The ammonia concentrations sensitivity in a high humidity environment is higher than low humidity environment, and the maximum sensitivity is 22.8 pm/ppm. The fiber-optic ammonia sensor designed and fabricated in this study utilizes the enhancement effect of water molecules on ammonia adsorption to improve the sensitivity of the sensor. This approach addresses the issue of poor moisture resistance in traditional ammonia sensors, thereby further expanding the application scenarios of ammonia sensors.