Design and Analysis of the Birefringent Characteristics of Hollow Core Bandgap Fiber

Polarization-maintaining fibers (PMFs) are the essential element to construct high performance optical fiber sensors. However, conventional PMFs such as PANDA and Bow-tie which based on the stress induced birefringence are susceptible to environmental perturbations, such as temperature and magnet fields, etc. Owing to the flexible design of the size, shape, and arrangement of the air holes in the cladding surrounding the core region, it is possible to induce high birefringence into the hollow-core photonic bandgap fiber (HC-PBF). Moreover, since the propagation light is confined mostly in the hollow region filled with air, the temperature or other perturbation effect can be largely reduced. In this paper the birefringent property of HC-PBF is studied and analyzed with the aid of the software COMSOL 5.3, and the relations between the birefringence and the fiber parameters such as the core diameter, size, shape, and spacing of the air holes are obtained. We found that the elliptical deformation either for the hollow core or for the air holes located in the cladding will induce relatively high birefringence inside fiber. And the width and position of the bandgap is mainly determined by the air filling ratio (f(air)). From our simulation the geometrical birefringence of HC-PBF can be as large as 6.8 X 10(-4) , and the confinement loss less than 0.02 dB/m in the wavelength range from 1.4 similar to 1.5 mu m.