Highly birefringent ZBLAN photonic quasi-crystal fiber with four circular air holes in the core

A highly birefringent ZBLAN photonic quasi-crystal fiber with a rectangular array of four relatively small circular air holes in the core region is proposed. Through optimizing fiber structure parameters using a full-vector finite-element method combined with perfectly matched layers boundary condition, its birefringence is up to 2.88 × 10−2 and the confinement losses of both polarized modes are less than 4.95 × 10−4 dB/m at 2 μm. To our knowledge, this is the first simulation study showing that a birefringence can be achieved with the order of 10−2 by all-circular-hole PQFs around 2 μm.