Fabrication Of Fiber Optic Sensors And Their Applications Using Femtosecond Micromachining

Since the invention of optical fiber,it has been widely used in wired communication due to many advantages such as faster transmission speed,long-distance transmission distance,strong anti-interference ability,and so on.Later,it was found that the change of the physical parameters such as the intensity,phase,wavelength and polarization of the transmitted light in the fiber can be changed by changing the structural parameters or the refractive index distribution of the fiber.Therefore,the optical fiber sensor has the advantages of high sensitivity,anti-electromagnetic interference and small size.Now it has been widely used in many fields such as industrial production,military and life.Since the emergence of the femtosecond laser,the femtosecond laser processing has the advantages of high efficiency and small heat influence due to its short pulse time and precise spatial distribution.It can realize the processing of the micrometer of the material and the processing structure.The machining accuracy is not affected by the nature of the environment and the material.This makes the femtosecond laser micromachining technology have advantage in the field of micro-processing,micro-optical device production and other fields,especially in the production of fiber optic sensors.This dissertation is divided into the following five chapters:In the first chapter,the advantages of fiber optic sensors compared with traditional sensors and the application of femtosecond laser micromachining technology in optical fiber sensing are introduced.In recent years,some researchers at home and abroad have made many achievements in the production of fiber optical sensors by femtosecond microprocessing.In the third chapter,the development history of femtosecond laser and its advantages in material processing are introduced.The nonlinear effect of the femtosecond laser on the processing of transparent materials and its energy transfer process are introduced.In the fourth chapter,the femtosecond laser micromachining system is introduced,and the optimal conditions of micromachining are discussed.The radial ablation length of the optical fiber was 20?m,the loss was 5.47 dB,9.91 dB,14.18 dB and the ablation length was 10?m,the loss was 10.03 dB and the ablation length was 30?m loss of 9.85 dB U-shaped micro-slot.These structures were tested by refractive index sensing to produce a refractive index sensor with a sensitivity of 5700 ?W/RIU and had a good linear response in the range of 1.3331-1.3731 of the refractive index.In the fifth chapter,we use the femtosecond laser micromachining technique to fabricate microchannels with radial ablation length of 20?m and loss of 3.28 dB,10.10 dB and 14.35 dB,respectively.And the influence of the microchannel on the polarization state of the transmitted light is tested.It is found that the transmitted light can be modulated by the circular polarization into partial polarized light,and the polarization modulation capability increases with the micro slot depth.