Fiber Optic Humidity Sensor Based On GO Coating

Compared with the traditional humidity sensor,the fiber optic humidity sensor has the advantages of small size,high temperature resistance,electromagnetic interference resistance,fast response speed,compact structure,simple manufacturing process and so on.Here,the research status and development trend of traditional optical fiber humidity sensors are first introduced.After that,the optical fiber evanescent field sensing technology and graphene oxide two-dimensional material are combined to design and produce a high-sensitivity evanescent field fiber optic humidity sensor based on micro capillary and graphene oxide(GO)film.The main research contents are as follows:This paper proposes a new evanescent field sensing structure based on the fused silica capillary and optical fiber.The sensor is made by welding a single-mode optical fiber on the end surface of the capillary by an optical fiber fusion splicer.The total length of the sensing area is only 1.5mm.When light enters the capillary wall from the introduced optical fiber,multiple modes can be stimulated in tubing wall and interfere with each other.The output signal of the sensing structure exhibits a sharp interference spectrum.As a new type of two-dimensional material,graphene oxide surface is modified with a large number of oxygen-containing functional groups and has excellent hydrophilicity,which makes it have unique advantages in humidity sensing.In this paper,graphene oxide material is used to modify the proposed optical fiber evanescent field sensor.First,we use sodium hydroxide to adjust the pH of the graphene oxide solution,and then apply 1,3,and 5 cycles of graphene oxide layer on the outer wall of the capillary by dip coating,respectively.Then,we conducted experimental and theoretical studies on the evanescent field excited by the interaction between graphene oxide and the capillary wall.The performance of the sensor was tested under the conditions of a temperature of 25 ° C and a relative humidity of 30% RH-70% RH.In this paper,the dip coating method is used to combine the multi-layer thin film technology with the optical fiber sensing technology.The sensing area uses micro capillary instead of traditional optical fiber.The obtained graphene oxide-based micro capillary fiber evanescent field sensor shows the humidity Sensitive response,its transmission spectrum has sharp peaks and troughs,and has a good signal-to-noise ratio as a sensor signal.And because the period of graphene oxide coating is controllable,the sensor has tunable humidity sensitivity.The humidity sensor has a compact structure,the preparation method used is simple,the preparation cost is low,and it is expected to be applied in an all-fiber network for environmental sensing and health monitoring.