Research Of Tilted Fiber Bragg Grating Humidity Sensor Based On Agarose Film

Relative humidity(RH)measurement plays an important role in many fields such as people's daily life,national defense industry,transportation and storage,and precision measurement.Therefore,accurate detection of relative humidity changes is of great significance for improving human living conditions,regulating agricultural production,and improving industrial production processes.The existing humidity sensors on the market are mainly divided into two categories,fiber optic humidity sensors and traditional electricity-type humidity sensors.Compared with the electric sensor,the fiber optic humidity sensor has the advantages of anti-electromagnetic interference,flame retardant and the ability to be settled in small places.It has a good application prospect in national defense research,power engineering,etc.In this paper,a fiber grating humidity sensor is prepared by coating agarose on the surface of a tilted Bragg fiber grating(TFBG).A humidity sensor is prepared by modulating the spectrum of TFBG based on the property that the refractive index of agarose changes when the relative humidity(RH)changes.The specific content of this paper is:(1)Study on the theory and sensing characteristics of the tilted fiber grating and the sensing characteristics of the agarose of the moisture sensitive material.And the proof of tilted fiber grating sensing characteristic formula and the water molecule diffusion mechanism formula in the film.These prove the rationality of the combined humidity sensor.(2)The preparation of agarose film.Its surface structure showed that it is favorable for the absorption of water molecules.The refractive index of the agarose film under different conditions are tested by prism coupler.The trend of its refractive index versus humidity is then obtained.(3)Using the OptiGrating software,TFBG was simulated for three variables: TFBG temperature,coating refractive index and coating thickness.Complete basic experiments ensure the smooth completion of the final sensor(4)Finally,a fiber grating humidity sensor was prepared by coating agarose on the surface of a TFBG by gel dropping method.The humidity sensor has a sensitivity of 2.75 pm/% RH and 0.255 dBm/% RH in the range of RH of 45% to 85% and 45% to 75% respectively.At the same time,the response time of the humidity sensor can reach 0.6s,the recovery time is 4.3s.The repeated test of the sensor shows that the repeatability is good,and it is expected to be applied in the life production with short response time requirements.