Study On Micro Optical Fiber Humidity Sensor

Since the practical quartz fiber was produced,the application of fiber technology in acquiring,transmitting and processing information has been widely studied.With the continuous development of society,sensors in the fields of industry,agriculture,aerospace and other fields need to be more compact,portable,simpler in structure and sensitive.Fiber optic sensors have been widely studied for their immunity to electromagnetic interference and their ability to work normally and stably in extremely harsh environments.At the same time,it has been proved by experiments that the application effect of optical fiber sensors in stress,humidity,temperature and gas is very significant.In this paper,a miniaturized,easy-to-produce EFPI optical fiber humidity sensor based on the moisture-sensitive film is designed.In this paper,the types and the basic sensing principle of EFPI optical fiber humidity sensor are introduced in detail.On the basis of analyzing the principle of organic polymer sensitivity to humidity,PVA is selected as the humidity sensitive film in this experiment,and a kind of EFPI optical fiber humidity sensor based on PVA film is realized.The process of making the sensor is as follows: A gold film which can improve the reflectance of the end face is plated on the end of the flat fiber,10wt% PVA hydrogel is prepared by sol-gel method,and a PVA membrane is coated on the gold film by the lift method to form a FP cavity.In order to eliminate the temperature cross sensitivity,a FBG is added next to the FP cavity.According to the principle that different saturated salt solutions have different humidity values in a closed environment,a saturated salt solution is used as a humidity generating device to simulate the environmental humidity.The phase demodulation method based on cross correlation algorithm is used for cavity length demodulation.In this paper,sensors with different cavity lengths are made for humidity experiment and temperature experiment.The sensor with initial cavity length of 40.46?m has an average humidity sensitivity of 0.038?m/%RH in the humidity range of 18.2%RH-91.6%RH,and the average temperature sensitivity is 3.88nm/? in the temperature range of 20°C-90°C.Humidity sensitivity is ten times the temperature sensitivity.The average temperature sensitivity of the FBG having a center wavelength of 1553.5 nm in the temperature range of 20°C to 90°C is 9.415 pm /°C.It can be seen that the larger the initial cavity length,the higher the humidity sensitivity.