Abstract
Refractive index (RI) sensing is a promising technique in a variety of different scientific and industrial applications. In this paper, we theoretically and experimentally propose a newly-designed RI sensor. The proposed sensor consists of a particular long-period fiber grating inscribed in a two-mode fiber (LPFG-TMF) coated with tunable graphene oxide (GO), and the special structure allows an extremely high sensitivity in the transition region. The mode coupling between the LP11 core mode and the sixth-order cladding mode in the LPFG-TMF offers an apparently higher sensitivity feature. And the sensitivity is higher than that of a single-mode fiber-based LPFG (LPFG-SMF), which originates from the coupling between the core mode and the sixth-order cladding mode. Furthermore, the ultrasonic treatment time of GO, which impacts on the properties and performance of RI sensing, is also studied and investigated. Proof-of-concept results demonstrate significantly that comparing with the bare LPFG-TMF (621.66 nm/RIU) and LPFG-SMF coated with GO ultra-sonicated 5 hours (323.68nm/RIU), the LPFG-TMF coated with GO ultra-sonicated 5 hours performs optimized sensitivity of 11605.79 nm/RIU when surrounding RI ranges from 1.4558 to 1.4577. With its premium ability to operate high-sensitivity measurements, the RI sensing is expected to be useful for broad applications across the chemical fields.
Highlights
Refractive index (RI) sensor is an interesting area of ongoing research and has a wide range of applications such as pH detection, biochemical analysis, and food safety detection [1]–[3]
The long-period fiber gratings (LPFGs)-two-mode fiber (TMF) coated with graphene oxide (GO) ultra-sonicated 5 hours has the highest sensitivity of 11605.79 nm/RIU in surrounding RI (SRI) ranging from 1.4558 to 1.4577, which is relatively much higher than that of the bare LPFG-TMF (621.66 nm/RIU) and LPFG-single-mode fiber (SMF) coated with GO ultra-sonicated 5 hours (323.68nm/RIU)
Comparing with the LPFG-SMF coupled light from the core mode and the sixth-order cladding mode, the LPFG-TMF has a prominent advantage in RI sensitivity
Summary
Refractive index (RI) sensor is an interesting area of ongoing research and has a wide range of applications such as pH detection, biochemical analysis, and food safety detection [1]–[3]. In contrast to the LPFG inscribed in a single-mode fiber (LPFG-SMF), the LPFG-FMF has been theoretically proven to possess improved RI sensitivity [14] Another approach is to deposit an overlay on the LPFG. This paper discusses the fundamental and practical considerations of a novel RI sensor, which is mainly composed of a LPFG inscribed in a two-mode fiber (LPFG-TMF) and GO overlay. This combination is a powerful method that overcomes the sensitivity limitations of traditional LPFGs. This combination is a powerful method that overcomes the sensitivity limitations of traditional LPFGs
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