Birefringence in dielectric optical waveguides

The linear and circular birefringent properties of low-loss single-mode glass fibers are found to depend upon length. Depolarization is about 1 percent/km. Some anomalous behavior can be explained in terms of properties varying locally along the fiber and a resultant upper information rate of over 10
¹²
bits/s is estimated. Very small stress distributions or core ellipticities could give rise to the observed effects.