Development And Application Of Laser-induced Graphene/hollow-core Fiber Composite Sensors

In recent years,anti-resonant(AR)mechanism-based hollow-core fiber(HCF)has attracted a great deal of attention due to its transmission spectrum containing periodic high visibility spectral dips.Graphene has excellent photon-electron interaction capabilities as a new functional thin-film material with a single atomic layer thickness.Hollow-core fiber compounded with functionalized and tunable graphene can form new sensor devices,while graphene compounded with structurally stable and high-performing hollow-core fiber can effectively achieve optical performance with the two complementing each other.However,the transfer of graphene to the surface of the optical fiber requires very delicate and tedious operations,limiting the sensing performance of graphene fiber composite sensors and their commercial application.Laser-induced graphene opens up a new way of preparing graphene on flexible polymer substrates,avoiding the complex CVD graphene substrate transfer process,providing a good opportunity for the composite of graphene and hollow-core fiber.Therefore,this thesis has investigated the development and application of laser-induced graphene(LIG)/hollow-core fiber composite sensors.Due to exploring the sensing performance of hollow-core fiber(HCF),a gas refractive index(RI)sensor based on an inornate anti-resonant hollow-core fiber(HCF)was theoretically analyzed and experimentally demonstrated.The transmission spectra evolution of the proposed sensor and the resonance intensity variations to the surrounding gas RI were simulated.The effect of functional coating layers on sensing performance was investigated,and the impact of hollow-core fiber length on sensor sensitivity was summarized.In addition,temperature sensing was performed to resolve the temperature cross-sensitivity issue using a wavelength interrogation method.The proposed RI sensor exhibited the advantages of being easily manufactured and with ultrahigh sensitivity.The proposed sensor showed the benefits of simple structure,easy fabrication,and potential applications in chemistry research.Based on a study of refractive index sensors for gases in an anti-resonant hollow-core fiber.Laser-induced graphene and hollow-core fiber composite relative humidity sensors were proposed.A polyimide solution thermal curing process and picosecond UV laser-induced graphene achieved a tight composite of LIG and hollow-core fiber.The humidity response of the sensor was tested,the results showed that the transmission intensity of the sensor resonance inclination was inversely proportional to the relative humidity.Its sensitivity was related to the length of the HCF.The thickness of the LIG and the laser processing power for the laserinduced formation of the LIG film were positively correlated with the sensor sensitivity.The transmission visibility of the resonance dip was evaluated,and a sensitivity of 0.187 d B/% RH was obtained in an ultrawide relative humidity(RH)range of 5–95% RH.The sensor has good stability and a short response time of 0.178 s.The results suggest that LIG-coated HCF is a tunable and promising solution for humidity sensing.This thesis provides a new approach to studying graphene and optical fiber composite sensor devices.The gas refractive index sensor and relative humidity sensor were proposed,verifying the feasibility of LIG/hollow-core optical fiber composite and proving the superior sensing performance of the new composite sensor devices,which have broad application prospects in gas sensing and other industrial fields.