Abstract
Laser-induced graphene (LIG) is a porous material that can be coated on an antiresonance reflecting hollow-core optical fiber (HCF) for humidity sensing. In this study, a humidity sensor was constructed by dip coating a polyimide (PI) film on the surface of an HCF, followed by rearranging and graphitizing the PI film through laser irradiation, which led to the formation of LIG. The absorption of water vapor by the LIG film changed its refractive index, which varied the reflectivity of the HCF and produced resonance intensity changes in the transmission spectrum. Humidity experiments were conducted with LIG films under different laser parameters, that is, power. The transmission visibility of the resonance dip was evaluated. A sensitivity of 0.187 dB/% RH was obtained in an ultrawide relative humidity (RH) range of 5–95% RH. In addition, The sensor has short response and recovery times. Moreover, the proposed sensor has a wide operating temperature range and low cost, and its temperature cross-sensitivity issue can be solved using different demodulation methods. The results suggest that LIG-coated HCF is a tunable and promising solution for humidity sensing.
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