Study On Fabry Perot Optical Fiber Humidity Sensor Based On Polyvinyl Alcohol

Humidity plays an important role in daily life and manufacturing,which has attracted more and more attention.With the development of the times,higher requirements have been put forward for humidity measurement in the fields of biology,medical treatment,and artificial intelligence.High performance,easy to manufacture,and low cost attracted more and more attention.In recent years,optical fiber sensors has attracted more and more attention in the field of humidity sensors because of its advantages of fast response speed,strong anti-interference,and high sensitivity.In addition,with the rapid development of materials science,new types of moisture sensitive materials such as high molecular polymers has been concerned widely.At present,many reported optical fiber humidity sensor combined optical fiber with humidity sensitive materials have got many successful measurement results.However,many sensors have some problems such as process complexity,production cost,sensitivity,linear response range,repeatability,dynamic response.This paper designed and manufactured a Fabry-Perot interference optical fiber humidity sensor based on polyvinyl alcohol with a simple process,low cost,wide linear response range,good repeatability,high sensitivity and fast response speed.This sensor gives a kind of beneficial exploration for the optical fiber humidity sensor with low cost,easy fabrication and high performance.In this paper,the sensing mechanism and fabrication process were studied.By the successfully fabricated sensor,the humidity response,response repeatability,dynamic response and the response characteristics influence of sensor parameters were separately investigated by building a humidity sensing experimental system.After repeated measurement experiments for many times,meaningful experimental results were obtained.The humidity response of a typical sensor with a polyvinyl alcohol concentration of 70 mg/ml and 137 μm cavity length was performed,humidity response experiment results showed that the sensor can produce a significant spectral response to the relative humidity in the humidity range of 22%—98%.It has a humidity response sensitivity of 36.71 pm/%RH and a linearity of 0.99773 under rising humidity,and a humidity response sensitivity of 37.96 pm/%RH and a linearity of 0.99844 under falling humidity.The experimental results showed that the sensor has good repeatability and stability.The dynamic response of a typical sensor with a polyvinyl alcohol concentration of 70 mg/ml and 137 μm cavity length was performed.Its fastest response time and recovery time are 1 s and 2.5 s respectively.The experimental results showed that it has fast dynamic response capabilities.In order to furtherly investigate its humidity sensing characteristics,the responding character influence of sensor parameters,such as cavity length of the optical fiber Fabry-Perot cavity,the concentration of the polyvinyl alcohol humidity sensitive material,were also investigated experimentally.By the polyvinyl alcohol with 70 mg/ml concentration,six sensors with different Fabry-Perot cavity lengths of 82 μm,95 μm,103 μm,110 μm,118 μm,137 μm were fabricated separately for humidity response experiment.The experimental results showed that the six sensors have good response sensitivity,and the curve of the cavity length of the Fabry-Perot cavity vs response sensitivity is linear with0.98439 linearity.With 137 μm cavity length,five typical sensors with different polyvinyl alcohol concentration including 50 mg/ml,60 mg/ml,70 mg/ml,80 mg/ml,and 90 mg/ml were got for humidity response experiments.The experimental results showed that five sensors have good response sensitivity and linear responding,and the curve of the polyvinyl alcohol concentration vs response sensitivity is also linear with0.99786 linearity.Therefore,appropriate adjustment of the polyvinyl alcohol concentration or Fabry-Perot cavity length is beneficial to improve the response sensitivity.