Graphene-oxide coated LPGs for humidity sensing applications

Abstract

In this paper, we report a highly effective relative humidity (RH) sensor implemented on graphene oxide (GO) coated long period grating (LPG). The GO nanocolloides bonded onto a cylindrical fibre cladding enables the LPG with strong evanescent waves to absorb more water molecules increasing its RH sensitivity. In an LPG, the phase matching condition occurs when a forward propagating core mode is coupled with the co-propagating lower order cladding modes generating evanescent waves to interact with the surrounding medium. This unique effect of LPGs can be more enhanced with multilayer GO deposition. There is an expansion of GO film with the absorption of more water molecules as RH increases. The absorption of water molecules on GO coating increases the conducting carrier (holes) density on it, thus decreasing the refractive index of GO film. The combined effect of increasing evanescent waves and modulated refractive index makes the GO coated LPGs as effective RH sensors. Our recently achieved results have shown the RH sensitivity of the GO coated LPG is about 0.01 dB/%RH. We have also investigated the effect on GO layer thickness, showing thicker layer increases the RH response of the LPG cladding mode resonances in lower wavelength region.

Metal Oxide Coated Optical Fiber for Humidity Sensing Application: A Review

“…The sensitivity demonstrated in study is slightly higher than the study reported by Dissanayake et al (2018), where a sensitivity of 0.15 dB/%R was recorded. Additionally, the sensitivity obtained in this study was 18 times higher than the result reported by Sahoo et al (2020), which was 0.0084%/RH [69] [70]. The summaries of the three research studies that utilized long period grating as a sensing mechanism are presented in Table I.…”

“…In 2020, research executed by Sahoo et al, also used GO as the coating material for LPG with the same deposition method [70] The graph demonstrates a noticeable reduction in the attenuation bands of the three coupled cladding modes after GO was coated on LPG. This reduction was more pronounced at for the peak observed at 1650 nm.…”

Long-Period Fiber Grating Based on Side-Polished Optical Fiber and Its Sensing Application

“…When water penetrates the GO, the hydrophilic group can maintain the relative interlayer distance. Therefore, as more water molecules are absorbed, the effective RI of GO decreases [31], [32]. This may change the effective RI of the propagating mode is altered, thereby affecting the wavelength shift.…”