Patent ID: 7352939

Claim:
An optical fiber configured to support polarization insensitive operation of a microbend-induced grating formed in the core thereof, the fiber comprising: a central core region defined by a radius r c and a predetermined refractive index, defined as a refractive index difference Δn c as measured with respect to the refractive index of silica; a trench area surrounding the central core region, the trench area having a refractive index difference Δn t less than the refractive index of the central core region; and a ring area surrounding the trench area, wherein the refractive index difference of the ring area (Δn r ) is selected to be greater than 0.015, with a transition of no greater than one micron between the refractive index difference of the trench area and the ring area, the core region refractive index difference (Δn c ) being maintained to be approximately three-quarters the value of the refractive index of the ring area (i.e., Δn c ≈0.75*Δn r ).