Relative Humidity Sensor Based On Fiber Grating

Along with the development of industrial or agricultural production and the advances in technology, people pay more and more attention on accurate the detection of ambient humidity. In the petrochemical, textile, coal and other fields, the measurement of humidity is often needed. These explosive situations put special requirements on the performance of the sensor. Because of its own characteristics, the relative humidity sensors based on fiber grating can take advantage in these situations and have vast development prospects.Fiber grating, as a kind of optical passive components, has many fine properties, such as small size, anti-electromagnetic interference, corrosion resistance, high sensitivity and good stability. When it is affected by the temperature or stress in the outside, the center of the reflection or transmission spectrum wavelength will drift, and the amount of drift has a linear relationship with the change of temperature and stress. This characteristic provides a good possibility for testing of physical parameters. Humidity sensitive material is affected by the environmental relative humidity, in the same time its certain physical characteristics will be changed accordingly. With humidity-sensitive material and fiber grating working together, the humidity changes can be passed to the fiber grating. In this way, the light in the fiber grating can load the humidity information, by which the humidity measurement can be realized.In this thesis the basic theory and development of the humidity sensor are introduced, especially the significance and necessity of the research on the relative humidity sensor based on fiber grating. Using the theory of the coupled mode and simulation, the mechanism of fiber grating sensing and humidity sensitive material is analyzed. Polyimide and polyvinyl alcohol was investigated as two kinds of humidity sensitive material for coating. The fiber grating sensors for relative humidity measurement are also the focus and the performance of the sensors was improved effectively. Finally, the humidity sensor testing system is designed, and is used to test the four kinds of the relative humidity sensor based on fiber grating. The curve of relationship between the reflection and transmission grating wavelength and the humidity was gotten. The testing result of the stability was obtained.In this thesis, the relative humidity fiber grating sensors coating with polyimide and polyvinyl alcohol have been studied theoretically and experimentally. The production process has been made better to improve the detection performance of sensors. It is of practical significance for the application of fiber grating humidity sensors.