Research On Fiber Optic Humidity Sensor Based On Graphene

Humidity plays an important role in all aspects of human production and life.Since ancient times,people have continuously improved their instruments to meet the requirements for humidity testing.With the advancement of technology and the development of social economy,people's requirements for the accuracy and performance of humidity sensors are also constantly increasing.For the humidity testing industry,it's the time for challenges to coexist with huge development opportunities.The electronic humidity sensor with high precision and fast response rate has been derived,which is different from the traditional hygrometer.Subsequently,various moisture sensitive materials appeared which greatly expanded the field of use of humidity sensors.High-performance,miniaturized humidity detection devices have become the development trend of hygrometers.The emergence of two-dimensional nanomaterial represented such as graphene provides a new direction for the development of humidity sensors.In recent years,the structures of humidity sensing combined with two-dimensional nanomaterial have been continuously proposed,and it has become a new research hotspot.In this paper,one of the derivatives of graphene,Graphene Oxide(GO),was selected as a moisture sensitive material to propose humidity sensing structures.Based on the moisture sensitivity of graphene oxide and fiber optic sensing technology,several kinds of fiber-optic Mach-Zehnder interferometric sensors coated with graphene oxide film were proposed to study the sensitivity of the humidity sensor.The main works of this paper are as follow:1.This paper introduces the development background of humidity sensor,and discusses the development status of optical fiber sensing technology.Briefly introduce the sensing mechanism of four typical interference fiber sensors;the research and application status of various humidity sensors are discussed and their shortcomings are analyzed.2.Introduce the structure of graphene oxide,basic characteristics,and analyze the specific principle of graphene oxide for humidity sensing.The sensing principle of the Mach-Zehnder interferometric sensor is elaborated.Explain the principle of inter-mode interference on which the single-fiber fabrication Mach-Zehnder interference structure is based,and the light transmission mechanism in the main sensing structure-cone structure below.Make a theoretical foundation for the sensing structure proposed in this paper.3.Graphene oxide film coated double taper fiber optic humidity sensor is proposed.Two conical zones separated by 5 cm were fabricated by a multiple discharge of the fusion splicer to form an MZ interference structure.When light passes through the first tapered region,a portion of the light leaks from the core to the cladding.In the second tapered region,the light transmitted in the cladding re-enters the core,and the two modes of light are coupled to form interference.A graphene oxide film was coated on the material sensitive area(5 cm)of the structure,the humidity sensing structure was fabricated and an experimental detecting device was built.Changes in the relative humidity of the external environment can cause the effective refractive index of the cladding to change,which in turn causes the interference spectrum to drift.The experimental results show that when the relative humidity of the environment rises from 48.1% to 91.1%,the interference spectrum shifts to the wavelength increasing direction(red shift),the drift amount is 10.8 nm,and the sensor sensitivity is 0.234 nm/%RH.4.A graphene oxide film coated core-offset fiber optic humidity sensor based on MZ interferometer is proposed.Two core-offset structures and a taper-core-offset structure are separately produced.The sensing structure was also combined with graphene oxide for humidity sensitivity experiments.The experimental results are as follows: the sensitivity of the double-core-offset MZ humidity sensor is 0.05 nm/%RH,and the sensitivity of the taper-core-offset MZ humidity sensor is 0.09 nm/%RH.5.Based on the fiber optic humidity sensor proposed in this paper,a humidity detection system is designed and fabricated.Through photoelectric conversion,the optical signal collected by the optical fiber structure is converted into an electrical signal and amplified,and the acquisition card is input to the computer to realize real-time measurement.The structure proposed in this paper has the advantages of small size and strong anti-electromagnetic interference capability,which is unique to the optical fiber sensing structure,and is easy to be used for micro-structure and integrated detection devices.At the same time,the structure proposed in this paper is simple to make and low in cost,and can be widely applied to humidity detection applications in many fields.