ABSTRACT
The second-order mode cutoff in elliptical core fibers has received some controversial attention, and it is a very complicated mathematical problem involving an infinite set of Mathieu functions. However, a recent treatment somewhat analogous to some equivalent step-index-fiber considerations has made possible a fairly simple and accurate approximation. Because the materials used to manufacture optical fibers have different thermal expansion coefficients, it is possible to build anisotropic stresses into the fiber which lead to birefringence through the photoelastic effect. The manufacture of fibers with a controlled amount of intrinsic birefringence has received detailed attention, as the state of polarization of light transmitted by the fiber may be an important parameter for many applications. Some applications, such as the Faraday magnetic field sensor or circular polarization-maintaining fibers, require that the fiber exhibit a very small intrinsic linear birefringence.
