Polarization properties of birefringent fibers with stress rods in the cladding

The polarization properties of fibers with high-expansion aluminum-doped stress rods in the cladding are described. Polarization beat lengths and polarization-holding parameters comparable to those of state-of-the-art high-birefringence fibers are obtained. The diameter of the outer cladding is not sufficient to provide optimum constraint on the stress rods. Increasing the diameter of this region should significantly reduce both the beat length and the polarization-holding h - parameter. No anomalous behavior or thermal hysteresis is observed in the temperature dependence of the fiber birefringence below 600°C. Above 600°C, a permanent hysteresis which reduces the fiber birefringence is observed.