Highly birefringent ZrF4-BaF2-LaF3-AlF3-NaF photonic quasi-crystal fiber with twin grapefruits holes

Abstract

A novel design of highly birefringent photonic quasi-crystal fiber based on ZrF4-BaF2-LaF3-AlF3-NaF glass with twin grapefruit air holes near the core and twofold symmetry is proposed. The basic unit is composed of one square and its neighboring regular triangle. Using the finite element method, the birefringence and confinement loss are investigated simultaneously by changing the pitch of air holes and sizes of air holes. Numerical results show that the fiber maintains single mode operation in a wide wavelength range from 1.8 μm to 2.2 μm, and the birefringence is on the order of 10-2, two orders of magnitude larger than that of the conventional polarization-maintaining fibers, which is largest (around 2 μm) ever reported to our knowledge and the same order of magnitude as that obtained by fiber using elliptic air holes But this designed fiber is easy to fabricate compared with the fibers using elliptic air holes.