Patent ID: 7941012

Claim:
A phase-engineered fiber, comprising: a core region having a radius r core , a refractive index n core , and an effective refractive index Δn core with respect to an outer cladding region having an outer radius r cladding and a refractive index n cladding , where Δn core =n core −n cladding ; and a ring region surrounding the core region, the ring region having an inner radius equal to r core and an outer radius r ring , a refractive index n ring greater than n cladding , and a positive effective refractive index Δn ring =n ring −n cladding , wherein the values of r cladding , r core , r ring , Δn core , and Δn ring cause the fiber to have a refractive index step proximate to a peak amplitude value of a mode intensity profile of a higher-order LP 11 mode of an optical signal propagating through the fiber, wherein the higher-order LP 11 mode comprises a linear combination of modes, including cylindrically polarized TM 01 and TE 01 modes and mixed HE 21(even) and HE 21(odd) modes, wherein the refractive index step is sufficiently steep such that at least one of the cylindrically polarized modes has an effective refractive index sufficiently separated from effective refractive indices of the mixed modes to allow for coupling to the at least one cylindrically polarized mode with minimal coupling to the mixed modes, and wherein the fiber further includes a grating fabricated into a portion thereof to provide mode conversion between a fundamental LP 01 input mode and the higher-order LP 11 mode.