Research PaperHigh-performance fibre-optic humidity sensor based on a side-polished fibre wavelength selectively coupled with graphene oxide film

•A wavelength-selective coupling from SPF to the graphene oxide (GO) film is observed for the first time and used to sense relative humidity (RH).•Two working modes based on tracing wavelength and intensity variation are realized for the GO film coated SPF when sensing relative humidity.•High sensitivity of 0.145 nm/RH%, 0.915 nm/RH% and 0.429 dB/RH% are respectively achieved in wide range of 32%-85%, 85%-97.6%, 58.2%-92.5%.

A high-performance humidity sensor based on a side-polished single-mode fibre (SPF) coated with graphene oxide film was fabricated with a wheel side-polishing technique and spontaneous evaporation. The wavelength-selective coupling gave rise to a loss dip in the transmitted spectrum when a phase match condition was satisfied at a given resonant wavelength. The swelling effect of GO under high RH, which was confirmed by XRD and a spectroscopic ellipsometer, could increase the GO film thickness and led to a redshift at resonant wavelength. Experimental results show that the GO-film-coated SPF (GFC-SPF) is capable of working in two modes: tracing-wavelength mode and intensity variation mode. For the two working modes, the GFC-SPF has high sensitivity, good reversibility, good repeatability and excellent linearity. For the tracing-wavelength mode, a very high sensitivity of 0.145 nm/RH% and a high linear correlation of 99.6% were achieved in a low RH range of 32%-85%, while an ultrahigh sensitivity of 0.915 nm/RH% and a linear correlation of 98.7% were achieved in a high RH range of 85%-97.6%. For the intensity variation mode, a high sensitivity of 0.427 dB/RH% and an excellent linearity correlation of 99.8% were achieved in a wide RH range of 58.2%-92.5%. Such a high performance allows GFC-SPF to have widespread potential applications, such as in the fields of biology, chemical processing and food processing.