Abstract: A single-mode, single-polarization optical fiber ("PZ fiber") can have a large single-polarization wavelength bandwidth when .eta. (as herein defined) for one symmetry axis is positive when calculated from the refractive index profile determined with one of two orthogonal orientations of polarized light and is negative when calculated from the refractive index profile determined with the other orientation, and for each other symmetry axis of the novel optical fiber .eta. is positive for both orientations of plane polarized light. Preferably the absolute values for .eta. when positive and .eta. when negative are about equal for said one symmetry axis. A preferred PZ fiber can be formed by depositing siliceous layers onto the interior surface of a hollow substrate tube of quartz to provide a preform. After forming two parallel flat faces in its outer surface, the preform is pulled to form a PZ fiber having an ellipitcal stress-applying region.

Abstract: A single-mode, polarization-maintaining optical fiber has both excellent signal attenuation and resistance to adverse bending effects because (1) its cladding and any portion of the jacket that is within five times the radius of the mode-field in its core have a substantially uniform index of refraction that is at least 0.005 less than that of pure silica, and (2) the index of refraction of the core is at least as great as, but preferably not substantially greater than, that of pure silica. Preferably, the stress-applying region of the fiber is elliptical, and the jacket is pure silica.