Patent ID: 7340139

Claim:
A method of making a polarization insensitive optical fiber for use in mode conversion, the method comprising the steps of: forming a central core region of a material having a predetermined refractive index, defined as a refractive index difference Δn c as measured with respect to the refractive index of silica, the central core region formed to a predetermined thickness; forming a trench area to surround the central core region, the trench area formed from a material having a refractive index difference Δn t less than the refractive index difference of the central core region; and forming a ring area to surround the trench area, the ring area formed from a material having a refractive index difference (Δn r ) greater than 0.015, with the formed thicknesses of the trench area and ring area controlled such that a transition of no greater than one micron is formed 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 ), the sub-micron transition and radial gradient in refractive index resulting in splitting the resonant wavelengths of the polarization-dependent TE and TM modes from the resonant wavelength of the polarization insensitive odd/even HE mode.