Patent ID: 7177510

Claim:
An optical fiber configured to support polarization insensitive operation by supporting propagation only along the odd/even HE 2m modes, the fiber core comprising a central core region of a selected refractive index (Δn c ) and a predefined radial extent (r c ); a trench core region surrounding the central core region, the trench core region having a selected refractive index (Δn t ) less than the central core region refractive index, said trench core region having a predefined radial extent (r t ); and a ring area surrounding the trench core region, the ring area having a selected refractive index (Δn r ) greater than the trench core region refractive index and a predefined radial extent (r r ), the refractive indices and radii of each element configured to provide a relatively large gradient in refractive index as a function of distance from the fiber core center, sufficient to provide a resonant mode splitting between the propagating TE 0m and TM 0m modes with respect to the polarization insensitive odd/even HE 2m modes such that an insubstantial amount of signal is coupled into the TE and TM modes, where m defines the order of the radial mode for the wavelengths supported by fiber.