Research On The Fiber Optic Humidity Sensor Based On The Graphene Oxide

For the introduction of some functional oxygen-containing groups,such as hydroxyl,carboxyl,epoxide and carbonyl,Graphene oxide(GO)shows some new features,such as dispersibility and hygroscopicity.Furthermore,owing to the lager aspect ratio,water molecules-absorption abilities of GO film have been enhanced greatly.Since the fiber-optic sensor holds numeral advantages over conventional electrical-based sensors,such as the high sensitivity,compact structure and immune to electromagnetic interference,it has been widely applied in sensor field.A series of optical fiber relative humidity sensors based on the GO film had been studied in this paper and the main contents are shown as follows:1.Some typical optical fiber sensing structures and the sensing principles were introduced.The brief introductions of fiber-optic humidity sensors which were developed from the existing optical fiber sensing structure were also presented.And the performances of the new sensors made from the combination of the GO film and the optical fiber sensors were also indicated.Considering the cylindrical structure of fiber-optic sensor,the optically driven deposition method was proposed.2.The polarization-dependent humidity sensor based on an in-fiber Mach-Zehnder interferometer(MZI)coated with GO was presented.The sensor head was constructed by fusion splicing a 15 mm-long PMF between a waist-enlarged taper and a core-offset.The GO film was coated on the polished surface of the proposed sensor head by the method of optically driven deposition.The effective refractive index of the GO film varies with the different external environments,and lead to changes of the resonance dips at fast axis and slow axis.By detecting the transmission intensity changes of the resonant dips at slow axis,the maximum sensitivity of 0.349 dB/%RH at the RH range of 60%~77% was obtained.3.A new relative humidity sensor based on a TFBG coated with GO film was presented.Thanks to the strong interactions between the excited backward propagating cladding modes and the exoteric GO film,amplitudes of the cladding mode resonances varies with the water suction and discharge processes of the GO film.By detecting the transmission intensity changes of the cladding mode resonant dips at the wavelength of 1557 nm,the maximum sensitivity of 0.129 dB/%RH under the RH range of 10%~80% was obtained.4.A fiber-optic humidity sensor based on an in-fiber MZI coated with GO/PVA composite film was presented.The GO/PVA composite film was coated on the surface of the proposed sensor head.By comparing the experiment results of the sensor head coated with different GO/PVA composite films,composite film formed by the ratio of 0.3 g PVA mixed with 10 ml GO dispersion shows a better performance of humidity sensitivity,and the maximum sensitivity of 0.193 dB/%RH at the relative humidity range 25%~80% was obtained.