Optical Fiber Humidity Sensor Based On Fabry-Perot Interferometer With Solid Cavity

The real-time monitoring of humidity is of great significance in the protection of cultural relics,food safety and medicine storage.Compared with the traditional humidity sensor,fiber humidity sensor has been widely used because of its advantages of anti-electromagnetic interference,compact structure and corrosion resistance.In order to expand the application of optical fiber in humidity sensing and solve the problems of low humidity sensitivity and slow response time.In this paper,three kinds of fiber humidity sensors with different structures are introduced,and their working principle,fabrication process and sensing characteristics are deeply studied,and promotes the development of optical fiber humidity sensors with excellent performance.Details of this article include:1.A kind of optical fiber humidity sensor based on Fabry-Perot interferometer(FPI)with solid cavity is studied.The sensor consists of a small cut-off quartz capillary with an inner diameter of ～4m,which is fused to the end of a single-mode fiber and coated with a humidity-sensitive film.In this paper,the working principle of the sensor is analyzed in depth,and its preparation process and test data are introduced in detail.The experimental results are in good agreement with the theoretical analysis.The humidity sensitivity is up to ～0.752nm/%RH(relative humidity),the response time is short(<100ms)and the stability and repeatability are good.It can also be used in human respiratory monitoring.At the same time,the sensor is sensitive to temperature(～1.35nm/°C)and can be used in temperature sensing measurement.2.The fiber humidity sensor based on parallel FPI with vernier effect is studied.Two FPIs are composed of capillary with an inner diameter of ～4μm fused to the end of single mode fiber.One of which is coated with a humidity sensitive film to act as sensing FPI and the other uncoated as a reference FPI.The two FPIs have similar optical length,resulting in vernier amplification effect.A highly sensitive humidity sensing measurement is achieved by using the contour demodulation of the superposed spectrum.The highest sensitivity is 1.12nm/%RH.3.A series FPI humidity sensor is preliminarily explored.The device consists of single-mode fiber,capillary and large mode area fiber(LMAF)fused in turn,and the end face of LMAF is coated with humidity sensitive film.The experimental results show that the humidity sensitivity is about ～308.7pm/%RH,and has good stability and fast response(～ 60ms).