Fabrication And Sensing Characteristics Of Optical Fiber Sensor Based On Coating Functional Material

Optical fiber is a kind of sensing head that can work on the micron scale and is widely used in optical fiber communication and sensing.The rapid development of optical fiber sensing technology cannot be separated from the emergence and application of various new sensor structures.The new structure not only enriches the types of optical fiber sensors,but also deepens people's understanding of the sensing mechanism and promotes the continuous progress of optical fiber sensing technology.From the aspects of simplifying the preparation process,reducing the cost of devices,improving the detection sensitivity and increasing the sensing parameters,people keep creating new microstructure sensors,which have highlighted the potential application value in harsh environment sensing,chemical substance detection,biological medical monitoring and other fields.At present,combining functional materials and optical fiber to make sensitive optical fiber temperature and humidity sensor becomes popular.Since this kind of sensor has the advantages of high sensitivity,good repeatability,and resistance to electromagnetic interference.Since the fiber itself is not sensitive to humidity,making a humidity sensor has certain scientific research value,which provides certain basic research for the industrialization production of fiber humidity sensor in the future.In this paper,coating temperature and humidity sensitive material on the function structure of fiber to fabricate new functional sensor is the main research direction.From the perspective of optical fiber sensing,this paper expounds the basic theory of temperature and humidity sensing,the functional materials and the coating process.Excellent optical fiber temperature and humidity sensors are selected through the analysis of experimental results.From the point of view of engineering application,the temperature and humidity sensors of long-period fiber grating,multi-mode interference and all-fiber MZI interference are studied systematically.A set of high-frequency CO₂ laser pulse writing manufacturing platform was built for the fabrication of long-period fiber gratings.In addition,singlemode-multimode-singlemode structure was made by cutting and welding device?CSM?,and a total of 5 kinds of fiber structures were made.By comparing the existing temperature-humidity sensitive materials in the market and analyzing the physical characteristics and sensing characteristics of the sensitive materials such as hygroscopicity,sensitivity and stability,polyimide?PI?and polydimethylsiloxane?PDMS?were selected as the temperature sensitive materials and humidity sensitive materials in this paper.Meanwhile,the coating methods of functional materials are studied,two sensitive material forming methods are summarized:drip coating and suspension coating.The method of saturated salt solution vapor pressure was used to produce standard humidity source.The constant temperature and humidity chamber was used to create temperature environment.The high-precision digital temperature control box was used to produce the standard temperature source to achieve the calibration of fiber optic temperature sensor.Then the sensitivity and stability of the optical fiber sensor are tested and analyzed on the temperature and humidity test platform.It is concluded that polyimide and polydimethylsiloxane can be combined with functional structure fiber to produce excellent temperature and humidity sensor.