Graphene-Oxide-Coated Long-Period Grating-Based Fiber Optic Sensor for Relative Humidity and External Refractive Index

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. City Research Online 1  Abstract-Graphene oxide is a very attractive material for refractive index and humidity sensing due to its unique twodimensional structure, which results in faster response times and improved sensitivity over alternative materials. In this paper, response of a graphene oxide-coated long period grating-based sensor to changes in relative humidity and external refractive index (as well as temperature to provide a correction for any changes) is reported. In fabricating the probes, an improved Hummer's method was used to synthesis the graphene oxide dispersion used as its basis, allowing coating of a functionalized long period grating by using a dip-coating technique. A consistent and stable response of the resonance dip intensity of the graphene oxide-coated long period grating was observed to the change in humidity, achieving a sensitivity of 0.15 dB / %RH with a linear correlation coefficient of 0.980 over the relative humidity range from 60%RH to 95%RH, at room temperature (25 ℃). A blue shift of the resonance band wavelength was recorded when the sensor was exposed to varying temperature conditions from 25 ℃ to 70 ℃ and the response was found to be linear, with a correlation coefficient of 0.997. When evaluating its performance as an external refractive index sensor, sensitivities of ~17dB/RIU in the lower refractive index region (1.33-1.38) and ~55 dB/RIU over the higher refractive index region (1.40-1.45) were achieved. The graphene oxide-coated long period grating sensor probe performed well, showing a good stability and repeatability over a number of test cycles in the performance evaluation carried out. Permanent repository link

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