Ultrahigh birefringence of elliptic core fibers with irregular air holes

We have investigated experimentally and theoretically the birefringence of the elliptic core fiber with irregular air holes. The wavelength dependence of the beat length and the birefringence was measured by the wavelength scanning method. The fiber exhibits ultrahigh birefringence of 1.12×10−2 at 1550 nm. We also calculated the modal birefringence of the fundamental modes in the fiber by using the plane wave expansion method. The calculated birefringence is in excellent agreement with the measured one.