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

We propose and experimentally demonstrate a high-performance relative humidity (RH) sensor by depositing graphene oxide (GO) onto tilted fiber grating (TFG). The largely tilted grating planes of the employed TFG can induce a set of polarization-dependent cladding modes and strong evanescent field to couple with the humidity-dependent dielectric of GO layer. The GO-deposited TFG presents the response sensitivities of 18.5 pm/%RH and 0.027 dB/%RH in the range of 30%∼80%RH by tracking the wavelength and intensity of a specific cladding mode resonance. By monitoring the human breath with different frequencies, the sensor exhibits an ultrafast response within ∼42 ms due to the thin GO film and unimpeded permeation of water molecules through GO interlayer. The easy fabrication, low hysteresis, fast response, and high repeatability and reliability of the proposed RH sensor may enable many potential applications including pharmaceutical processing, human health and environmental monitoring.