Polarization optics of twisted single-mode fibers

In twisted single-mode optical fibers the polarization of light is affected by an elastooptically induced optical activity and by a modification of any linear birefringence present. These effects are discussed theoretically and demonstrated experimentally. The activity/twist ratio is alpha/tau approximately 0.13 ... 0.16 universally in weakly guiding silica fibers. Twisted fibers may be used as polarization rotators. A fiber with a +/-68 degrees double twist operates as a fast/slow mode interchanger, suitable for delay equalization.