Study On Fiber Optic Humidity Sensing Technology Based On Nanoimprinted Waveguide Grating

Humidity,commonly used to characterize the moisture content in the air,requires accurate measurement results in various fields such as environmental monitoring,agriculture,and warehousing.Fiber optic humidity sensors are also widely used in the field of humidity sensing due to their passive,small size,and anti electromagnetic interference characteristics.At present,the main challenges of fiber optic humidity sensors include narrow measurement range,low sensitivity,and cross interference between temperature and humidity.Based on the above challenges,the research content of this thesis is as follows:(1)In order to achieve high-performance measurement of humidity sensing,a fiber optic humidity sensor based on single-layer guided mode resonance(GMR)waveguide grating was designed and implemented.In this thesis,GMR waveguide grating membrane with good resonance wavelength consistency was prepared by nano imprinting process,and polyimide(PI)was coated on its surface as a humidity sensitive material.Finally,the membrane and quartz fiber were packaged to prepare an optical fiber humidity sensor,which realized the sensing characteristics of wide measurement range,temperature insensitivity,high stability,and good repeatability.The experimental results show that the humidity sensor of this structure has a humidity sensitivity of51.5pm/%RH and a temperature sensitivity of 6pm/℃ in the humidity range of 10%-90%RH.The humidity repeatability measurement error is less than 1%RH.(2)In order to achieve higher sensitivity measurement of humidity sensing,a fiber optic humidity sensor with a double-layer GMR waveguide grating with narrower spectral linewidth was designed and implemented.The properties of double-layer waveguide gratings were simulated and analyzed,and the effects of different grating parameters,spacing,and angle on the double-layer GMR effect were studied.Based on this,a symmetrical double-layer GMR waveguide grating fiber optic humidity sensor was prepared.The experimental results show that the fiber optic humidity sensor based on a double-layer GMR structure has an improved humidity sensitivity from51.5pm/RH of the single-layer structure to 72.5pm/%RH in the humidity range of 10%-90%RH.The temperature sensitivity is 8.6pm/ ℃,and the humidity repeatability measurement error is less than 1%RH.Starting from structural design,simulation,packaging,and experimental testing,thesis studies the sensing characteristics of GMR waveguide gratings based on nanoimprinting,and verifies the feasibility of humidity sensing,laying a foundation for further practical application in working conditions.