Highly birefringent photonic crystal fiber based on a double-hole unit

We propose a novel highly birefringent photonic crystal fiber (PCF) based on a double-hole unit. Because of the effect of the double-hole unit in which double airholes can be effectively viewed as elliptical airholes, the proposed PCF can achieve birefringence similar to that of an elliptical-hole PCF with high birefringence even up to the order of 0.01 and still avoid the inherent challenge to fabricate an elliptical-hole PCF. The proposed PCF also has a lower confinement loss than an elliptical-hole PCF with the same air-filling fraction.