Graphene oxide-deposited tilted fiber grating for ultrafast humidity sensing and human breath monitoring

•An optical fiber-based humidity sensor with ultrafast response is proposed by depositing GO onto a tilted fiber grating.•The experimental results show sensitivities of 18.5 pm/%RH and 0.02 dB/%RH in the dynamic range of 30%–80%RH.•The sensor is successfully applied to monitor human breathing cycles with different breathing frequencies.•The sensor also possesses the merits of easy fabrication, low hysteresis, ultrafast response, and high repeatability.