Design And Simulation On Low-loss Mid-infrared Hollow Core Antiresonant Optical Fibers

Mid-infrared fiber refers to the optical fiber with transmission wavelength of2-20?m.This band of light is often used as a laser in military,medical,equipment processing,or as a carrier in the field of cable optical fiber communication,image and sensing,which has a critical application value.Therefore,these applications all put forward the urgent demand for the optical fiber waveguide which conducts the laser energy or the carrier wave,and the production of low loss and high-performance mid infrared optical fiber inevitably becomes an urgent problem to be solved at present.Nevertheless,the traditional optical fiber made of quartz will produce extremely high absorption loss when transmitting mid-infrared light.Whilst the soft glass optical fiber of sulfide and fluoride materials is not mature enough in material purification and fiber drawing technology,and has some flaws,which made it difficult for both those two types to achieve ideal transmission performance.Mid-infrared fibers based on solid core has not make a breakthrough in recent years.Therefore,it is of great value and significance to research and develop new materials or structures of mid-infrared fiber.Hollow core antiresonant fiber consists of an air core,and has a new light guiding mechanism different from total reflection.Because of its simple structure and superior performance,it has become a research hotspot in the field of optical fiber.Compared with hollow core photonic band gap fiber,hollow core antiresonant fiber has lower loss and wider transmission bandwidth,which makes it an ideal medium to realize waveguide of mid-infrared light.focusing on low loss applications of mid-infrared 2?m and 4?m optical transmission,two new structures of hollow core antiresonant fiber are proposed and simulated by means of COMSOL finite element method in this thesis: ginkgo leaf hollow core antiresonant fiber and nested crescent hollow core antiresonant fiber.Also,the transmission performance is tested by simulation.The main contents of this thesis are as follows:1.In this thesis,the optical guiding theory,mode field distribution and typical structure of hollow core antiresonant fiber are summarized.By means of finite element simulation,the mode field distribution,loss,dispersion and single mode behavior of the fiber can be calculated accurately.2.The relationship between the structure and the loss of the hollow core antiresonant fiber is analyzed,and an improved scheme is proposed.Based on this,a new type of Ginkgo leaf hollow core antiresonant fiber is designed.By means of simulation,the structure parameters of the new optical fiber are optimized to achieve the loss as low as 0.05 d B/km in 2?m band and 3d B/km in 4?m band.The performance of the optical fiber in loss,dispersion,single mode and bending characteristics is simulated and calculated.The reference of absorption loss when using traditional quartz material is given,and the advantages compared with traditional hollow core antiresonant fiber are also discussed.3.Based on the ginkgo leaf hollow core antiresonant fiber,a new type of nested crescent hollow core antiresonant fiber is proposed.After an optimization of parameters,the confinement loss is as low as 0.0015 d B/km in 2?m band and 0.07 d B/km in 4?m band.