Apparatus for selecting waveguide modes in optical fiber and the method

Abstract

An apparatus for selecting waveguide modes in optical fibers is disclosed, which comprises an optical fiber having of a core and a cladding sheathing the core. The optical fiber has a selected portion of the cladding removed and forms a recessed space in the cladding while preserving a predetermined thickness of the cladding remaining covering the core. The optical fiber is selected for allowing the transmission of light having multiple waveguide modes with radial and azimuthal electric field components. The apparatus further comprises a birefringent material filled in the recessed space. The birefringent material has the first and second refractive indices and the first refractive index is larger than the core index of the optical fiber, while the second refractive index is smaller than the cladding index of the optical fiber. The first and second refractive indices of the birefringent material are arranged in the radial and azimuthal directions of the optical fiber respectively, so that the transmitted light of the waveguide mode with the radial electric field component is coupled out from the core of the optical fiber to the selective portion of the cladding, and the transmitted light of the waveguide mode with only the azimuthal electric field component remains transmitted through the optical fiber.