Research On Humidity Sensor Based On Titled Fiber Bragg Grating

Fiber optic sensor has been paid mounts attention in these years for its high sensitivity,simple structure and anti-electromagnetic interference.It has been successfully used in sensing the temperature,stress,acceleration and other aspects.TFBG is more suitable than FBG in the measurement of refractive index.Relative humidity is an important parameter in concrete,but there is no good academic method to measure the humidity in concrete limited by the theory,modeling level and humidity sensor performance.It is necessary to design a sensor for concrete research.The main research content of this paper is design a humidity sensor based on titled fiber grating.We introduced the humidity detection and its importance in concrete shrinkage research,progress of fiber grating sensor and TFBG sensor.Then we deduce the coupling mode of the tilted fiber grating from the coupling mode theory of fiber grating.This paper focuses on the theory of cladding mode coupling and the coupling theory of radiation mold with different characteristics.Expounding the possibility of sensing in stress,temperature,refractive index Theoretically.Characteristics of PVA are introduced.Using prism coupler to measure the refractive index of PVA samples.And other experiment prove that PVA can change its refractive index with the change of ambient humidity.It shows that PVA is an ideal humidity sensitive material.A kind of humidity sensor based on TFBG was designed.PVA was coated on the TFBG,which can sense changes of surrounding humidity.The transmission characteristics of the cladding mode will also change.,then we can detect the wavelength shift of the cladding mode to achieve humidity sensing.