Loss Characteristics Of Infrared Hollow-core Bragg Fiber

With the development of optical fiber technology, the transmission wavebands gradually become farther and longer, shifting from near-infrared region below 2μm to mid-infrared even far-infrared. Unlike ordinary optical fiber for signal transmission, infrared Bragg fiber is always using transferring laser energy. Recent decades, we have launched a large number of theoretical studies in the field of infrared fiber, and gradually turned into the practical applications.At present, it has already been widely used transferring the CO₂ laser energy in medicine and industry, and sensor applications.In this paper, by comparing the material's optical and physical characteristics, and using the plane wave expansion method (PWM) to calculate the band gap, we select suitable materials ( As 2Se3/PEI ) and fill rate ( fμ0.8) in order to get a kinf of Bragg fiber for transmission 10 .6μm CO₂ laser energy. On this basis, combined with the full vector finite element method (FEM) and using COMSOL software simulation to optimize structural parameters of the hollow-core Bragg fiber, and ultimately achieve low-loss transmission of 10.6 laser energy. The specific parameters are as follows, the periodic lattice is 7μm, high and low refractive index material thickness are respectively 1. 4μm and 5 .6μm,together 20 cycles, the radius of the hollow-core is 150μm .The loss value can be reduced to 5. 14dB/km at 10.6μm ,far better than the current 0. 01dB/m.Taking into account the imperfections of the production process, the paper also analyzes the impact of the single cycle defect. Simulation results show that, when the complete structure of the periodic lattice is 7μm in the second band gap , defect which size slightly larger than the periodic lattice can help to reduce the loss of Bragg fiber at 10 .6μm. On the contrary, the loss becomes greater. That is,when the defect 7. 18μm appearing in the first layer near the hollow-core,it is best for reducing the loss. The results have great significance to the production and applications of infrared fiber.