Ultra-Sensitive Fiber Optic Gas Sensor Using Graphene Oxide Coated Long Period Gratings

Abstract

In this letter, we develop two types of refractive index based sensors using single-mode fiber (SMF-28) to sense hazardous toxic gases in underground mines. The first sensor design is simply a graphene-oxide (GO) deposited long period grating (LPG) and second sensor consist of two LPGs with an interspacing distance of 1 cm ( $\Delta \text{l}$ ) acting as Mach-Zehnder interferometer (MZI). In addition, we also confirm GO deposition on the SMF using ultraviolet–visible spectroscopy, atomic force microscopy (AFM), and field emission scanning electron micrograph (FESEM). Our experiment results show that the sensitivity of two-LPGs based fiber optic sensor (SLPG−2 = 76.32 dB/RIU) is higher as compared to the single LPG sensor (SLPG−1 = 54.65 dB/RIU). Hence, reported graphene oxide deposited long period grating sensor possess better sensitivity and can detect maximum $1.52\times 10^{-5}$ index variation in the optical telecommunication band.