Research On Humidity Sensing Characteristics Of Optical Microcavity

With the rapid development of the “Internet of Things” industry and miniaturization and integration of sensors,humidity monitoring has been widely used in defense technology,industrial production,medical technology,and daily life,and various industries have prepared and tested humidity sensors.There are specific requirements in terms of range,response speed,and service life.However,it is difficult to fully meet all requirements based on the existing technology.In order to prepare a humidity sensor that can better meet the above requirements,this paper proposes a humidity sensor based on an optical microcavity.The main research content includes:Firstly,the knowledge of the humidity sensor was introduced.The sensing mechanism,advantages and disadvantages of the existing humidity sensor were classified,and the fiber humidity sensor was introduced.The fiber humidity sensor was analyzed in detail and its research progress at home and abroad in recent years was carried out.Expressed.Secondly,based on Maxwell's equations,this paper analyzes the coupling theory of optical fiber microsphere and tapered fiber,and simply studies its sensing characteristics and the factors that affect the sensing characteristics.The theory of humidity sensing based on optical microcavity is performed.It was found that the resonance peak of the transmission spectrum of the micro spherical cavity-tapered fiber coupling structure drifts along with the change of the refractive index of the media.This theory verifies that the structure can be used in the point of humidity testing combined with the relevant knowledge of materials science.The diffusion mechanism of water molecules in molecular humidity and humidity sensitive films was studied.According to experimental requirements,agarose was selected as the humidity sensitive film of the sensor designed in this paper.Thirdly,the types of optical microcavities are briefly introduced respectively,and the advantages and disadvantages of various types of whispering-wall type optical microcavities are analyzed and compared.Taking the microring resonator as an example,the humidity sensing is performed by FDTD numerical simulation method.The characteristics were simulated and analyzed,and the linear relationship between the resonance peak shift of the coupled structure and the change of the ambient refractive index was obtained.This provided a certain reference for the experimental study;the preparation of the microsphere cavity,tapered fiber,and agarose humidity sensitive thin film was introduced in detail.The method and process provide a reference for the research of the same type of humidity sensor.Finally,a humidity sensor test system was designed and built,and the experimental flow was described in detail.The microsphere cavity-tapered fiber coupling performance and the sensing characteristics of the humidity sensor were tested and analyzed.The experiment found that the humidity was based on the cavity of the optical microsphere.The sensor has a moisture sensitivity of ~14.45pm/%RH when humidity is in the range of 15%RH to 80%RH when it is not coated with a moisture sensitive film,and it is in the humidity range of 15 after being coated with five layers of agarose moisture sensitive film.%RH to 80% RH with ~275pm/%RH.At the same time,it is verified that the humidity sensor has less hysteresis error and better reusability.The experimental results are in good agreement with the theoretical analysis.In this paper,theoretical and experimental studies have been conducted on coated and uncoated agarose moisture sensitive materials for optical fiber microsphere humidity sensors because of their very simple fabrication,small size,good stability,low cost,and large humidity monitoring.The advantages of range,very high humidity sensitivity and very rapid humidity response meet the needs of humidity sensing.It is hopeful that significant applications will be made in the future in industrial production and people's daily life,and it will also provide certain methods and experience for the production of more advanced humidity sensors in the future.