Optical fiber polarizer

Claim 1

A fiber-optic polarizer characterised by the combination of: an optical fiber (25) comprising a core (26) and cladding (27) having different refractive indices and forming a single-mode guiding region, said guiding region being located sufficiently close to the surface (29) of the fiber (25), along a selected length of the fiber, to allow coupling to a contiguous medium, and the outer surface (29) of the fiber (25) having a non-circular cross-section with a predetermined geometric relationship to said guiding region so that the location of said guiding region can be ascertained from the geometry of said outer surface (29), and a polymeric film (40) extending longitudinally along a selected length of said fiber and coupled to the fiber surface (29) that is closest to said core (26), said film (40) having different indices of refraction along axes having predetermined geometric relationships to said non-circular cross-section of the outer surface (29) of said fiber (25), one of said indices of refraction of said film (40) being less than the effective index of refraction of a desired wave in said guiding region of said fiber (25), and the other index of refraction of said film (40) being greater than the effective index of refraction of an unwanted wave in said guiding region of said fiber (25).

Claim 20

A method of polarizing signals in an elongated opticalfiber comprising a core and cladding having different refractive indices and forming a single-mode guiding region, said core having a non-circular cross-section defining two transverse orthogonal axes which, in combination with said different refractive indices, permit the de-coupling of waves polarized along said axes, said guiding region being located sufficiently close to the surface of the fiber, along a selected length of the fiber, to allow coupling to a contiguous medium, the outer surface of the fiber having a non-circular cross-section with a predetermined geometric relationship to said guiding region and said orthogonal transverse axes so that the location of said guiding region and the orientation of said axes can be ascertained from the geometry of said outer surface, said method being characterised by the steps of stretching a polymeric film along a first axis disposed in the plane of the film to increase the index of refraction of the film along said first axis to a value above the effective index of refraction of an unwanted wave in said guiding region, said film having a second index of refraction along a second axis that is perpendicular to said first axis, said second index of refraction being below the effective index of refraction of a desired wave in said guiding region, and locating the film with one edge thereof extending longitudinally of the fiber and coupled to the surface of said fiber closest to said core, with said first axis disposed generally parallel to the minor axis of the elliptical cross section of said core and with said second axis disposed generally parallel to the major axis of the elliptical cross-section of said core.

Claim 21

A method of polarizing signals in an elongated opticalfiber comprising a core and cladding having different refractive indices and forming a single-mode guiding region, said core having a non-circular cross-section defining two transverse orthogonal axes which, in combination with said different refractive indices, permit the de-coupling of waves polarized along said axes, said guiding region being located sufficiently close to the surface of the fiber, along a selected length of the fiber, to allow coupling to a contiguous medium, the outer surface of the fiber having a non-circular cross-section with a predetermined geometric relationship to said guiding region and said orthogonal transverse axes so that the location of said guiding region and the orientation of said axes can be ascertained from the geometry of said outer surface, said method being characterised by the steps of stretching a polymeric film along a first axis disposed in the plane of the film to increase the index of refraction of the film along said first axis to a value above the effective index of refraction of an unwanted wave in said guiding region, said film having a second index of refraction along a second axis that is perpendicular to said first axis, said second index of refraction being below the effective index of refraction of a desired wave in said guiding region, and locating the film with one edge thereof extending longitudinally of the fiber and coupled to the surface of said fiber closest to said core, with said first axis disposed generally parallel to the minor axis of the elliptical cross section of said core and with said second axis disposed generally parallel to the major axis of the elliptical cross-section of said core.