Femtosecond Laser Micromachining And PVA/GO Modification Were Used To Fabricate A Fiber Optic Humidity Sensor

In the field of material processing,femtosecond laser has been widely used for precision machining of various materials on the surface or inside,including ceramics,metals,and transparent materials.During the process of micro-machining,the femtosecond laser pulse interacts with the optical fiber material.Due to the ultra-short pulse time and the extremely high energy density after focusing,the laser energy absorbed by the material,volatilizing rapidly as the gas phase and takes away some heat energy.The thermal diffusion has little effect on the area in the vicinity of the focal point.So there is no need to consider the property change caused by thermal expansion of the material around the ablated region.The content of the article is mainly divided into 5 parts:In the first chapter,some advantages of optical fiber sensor are briefly described.The application of femtosecond micro-machining technology in fiber optic sensing is introduced.And the topics and research directions of this thesis are determined.The second chapter,the basic theories of light in step fiber are introduced: ray theory and mode theory.The third chapter gives a detailed description of femtosecond laser micro-machining.It mainly includes the development of femtosecond laser,the nonlinear action of the transparent material and the process of energy transfer.The fourth chapter mainly introduces the femtosecond laser micro-machining system.And at the same time,it explores the micro-machining conditions.U-type micro-groove structure sensor probe coated with humidity sensitive material was fabricated on the multi-mode optical fiber using optimal processing conditions.The humidity sensitive material is a graphene oxide(GO)and polyvinyl alcohol(PVA)composite film,and its effective refractive index decreases linearly with increasing ambient humidity.As a result,the refractive index in the U-shaped groove changes,which in turn causes a change of light power.Adding to the surface of the multi-mode fiber for micron-scale processing,the ablation length along the fiber is 20?m,the loss is 1.04 dB,3.73 dB,6.12 dB,and the ablation length is 10?m,the loss is 6.08 dB and the ablation length is a U-type micro-groove with a 30?m loss of 6.39 dB.Experimental results show that the humidity sensor has a good linear response in the range of 20%-90% relative humidity,the highest sensitivity is 209.2nW/%RH.The influence of the micro-groove structure on the humiditysensing is also discussed.The fifth chapter is the summary and prospect of the full text.A systematic summary of this thesis is made.And looks forward to the prospect of the development of the humidity sensor.