MoS₂-based all-fiber humidity sensor for monitoring human breath with fast response and recovery

A humidity sensor is demonstrated using a MoS₂-coated etched single-mode fiber (ESMF) and applied in human breath monitoring. Because of the interaction between MoS₂ nanosheets and the evanescent field of an ESMF, the light confined within fiber core could be tuned by ambient conditions. The optical frequency conductivity of MoS₂ changes with relative humidity variation, so does the transmission light power of the ESMF. A 14 fold enhancement of light power variation in response to human breaths is achieved compared with a bare ESMF. Fast response and recovery speed (0.066 s response and 2.395 s recovery time) enable this sensor to detect human breath in real time. The results also show the feasibility in monitoring different breath patterns related to the breath frequency and depth.