Design And Characteristic Analysis Of The Infrared Hollow-core Bragg Fiber With Compound Period

With the development of optical fiber technology, a lot of theoretical and applied research works have been commenced in optical fiber field. The transmission band of the optical fiber develops from the infrared region of the2μm to the longer infrared, far infrared region gradually. At the same time, infrared optical fiber which used in the transmission of laser energy has emerged. Currently, the infrared optical fiber with the unique characteristic has been widely used in the medical field and industrial areas especially in CO2energy transmission and sensing.In this paper, the infrared hollow-core Bragg fiber with compound period is designed, the size of two micro units in the compound period and the thickness of each layer were determined using the plane wave expansion method (PWM) simulation analysis, the suitable cladding materials were chosen. After the compound period of Bragg fiber has been determined, using the COMSOL software based on the full vector finite element method (FEM), the loss characteristic of the fiber is analyzed, and structure parameters of the Bragg fiber are optimized. The simulation results show that when the structural parameters of the optical fiber:core inner diameter R=250μm, compound period Λ=6.2μm, the thickness of two micro-units are Λ1=2.7μm and Λ2=3.5μm, the thickness of each layer material in the compound period is di=0.81μm、d2=1.89μm、d3=1.05μm、d4=2.45μm, the compound period number N=10, the fiber loss decreased to0.287dB/km in the10.6μm, far better than the single cycle structure5.14dB/km.Finally, the defects of the infrared hollow-core Bragg fiber with compound period were analyzed, and the loss caused by a single defect is further simulation analysis. The results showed that, if the defect size is smaller than the lattice period, the loss at10.6μm will reduce; conversely, the loss will be larger, and this effect is more pronounced at the near core. The simulation results show that if a defect size of5.74μm has been introduced, the loss of the optical fiber reduces obviously. Research results for the production of infrared hollow-core Bragg fiber with compound period have application value.