High Sensitivity Microfiber Interferometer Sensor in Aqueous Solution.

Saad Hayatu Girei,Hong Ngee Lim,Mohd Adzir Mahdi,Ahmad Rifqi Md Zain,Mohd Hanif Yaacob,Muhammad Zamharir Ahmad

doi:10.3390/s20174713

Abstract

The need for environmental protection and water pollution control has led to the development of different sensors for determining many kinds of pollutants in water. Ammonia nitrogen presence is an important indicator of water quality in environmental monitoring applications. In this paper, a high sensitivity sensor for monitoring ammonia nitrogen concentration in water using a tapered microfiber interferometer (MFI) as a sensor platform and a broad supercontinuum laser as the light source is realized. The MFI is fabricated to the waist diameter of 8 µm producing a strong interference pattern due to the coupling of the fundamental mode with the cladding mode. The MFI sensor is investigated for a low concentration of ammonia nitrogen in water in the wide wavelength range from 1500–1800 nm with a high-power signal provided by the supercontinuum source. The broad source allows optical sensing characteristics of the MFI to be evaluated at four different wavelengths (1505, 1605, 1705, and 1785 nm) upon exposure towards various ammonia nitrogen concentrations. The highest sensitivity of 0.099 nm/ppm that indicates the wavelength shift is observed at 1785 nm operating wavelength. The response is linear in the ammonia nitrogen range of 5–30 ppm with the best measurement resolution calculated to be 0.5 ppm. The low concentration ammonia nitrogen detected by the MFI in the unique infrared region reveals the potential application of this optical fiber-based sensor for rivers and drinking water monitoring.

Highlights

Water is a widely used solvent in chemical and biological processes
The results presented here indicate that the microfiber interferometer (MFI) sensor can detect a low concentration of ammonia nitrogen in water with a
We evaluated the stability of the sensor by immersing it into ammonia nitrogen for one hour

Summary

Introduction

Water is a widely used solvent in chemical and biological processes. Researchers have used optical fiber sensors and water as the solvent for sensing various chemicals such as ethanol [1], isopropanol [2], nitrates [3], and ammonia [4] in aqueous solutions. The sensing is based on a change of the refractive index (RI) of the aqueous solution. Microcomponents such as ammonia nitrogen in water provide important information about water quality in rivers and water supply processing plants as well as in drinking water [5]. Concentrations ranging as low as 0.2–2.0 ppm can be lethal to fish species [7]. Major industries such as the pharmaceutical and chemical industries, fertilizer production, sewage treatment plants, and cattle excrement are some of the sources

Results

Discussion

Conclusion