Research On Fiber Optic Relative Humidity Sensor Based On Mach-zehnder And Michelson Structures

In various fields of human activities,humidity is an important physical parameter that people pay attention to.It is of great significance to obtain the environmental humidity information effectively for the production and life process.Optical fiber humidity sensor has the characteristics of anti-electromagnetic interference,high sensitivity,high cost performance,good stability and reusability,etc.It can not only replace the traditional humidity sensor in daily production and life,but also meet the needs of people for humidity measurement in flammable,explosive,strong electromagnetic interference and other harsh environment.In order to further explore the humidity sensing performance of optical fiber humidity sensor,this paper studies two kinds of interferometric optical fiber humidity sensors and characterizes their humidity measurement performance in detail.The main research contents and results are as follows:(1)A simultaneous relative humidity(RH)and temperature sensor based on a single mode fiber(SMF)Mach-Zehnder interferometer(MZI)with polyimide(PI)coating is proposed and experimentally demonstrated.Experimental results show that the RH response sensitivity of the sensor is-0.12458 d B/%RH,-0.20216 d B/%RH and-0.15201 d B/%RH when the length of the sensing fiber is 2.5 cm,3 cm and 3.5 cm,respectively.The temperature sensitivity is 0.0577 nm/~oC at the length of the sensing fiber is 3 cm.Consequently,the advantages of simple fabrication,low cost,high RH sensitivity and simultaneous RH and temperature measurement ability mean the sensor has great potential applications in the field of RH measurement.(2)A fiber-optic RH sensor with PI coating based on Michelson interferometer(MI)was fabricated and experimentally demonstrated.The sensor shows a linear response to humidity in the range of 35-85%RH,exhibiting sensitivities of 0.0983 nm/%RH and-0.09027 d B/%RH when using wavelength and intensity demodulations,respectively.The temperature response sensitivity is 0.0417 nm/?in the range of25-55?.(3)By using PI and Ca Alg moisture sensitive materials on the same Michelson sensor structure,the humidity characteristics of the sensors were compared experimentally.The experimental results show that the sensor has better humidity response ability when using Ca Alg moisture sensitive material.The excellent humidity response characteristics of the sensor demonstrate the effectiveness of Ca Alg hydrogels as moisture sensitive materials.The proposed sensor can be easily manufactured and has a good stability for RH measurements.