Abstract: A bending-resistant large core diameter high numerical aperture multimode fiber includes a core and a cladding surrounding the core. The core has a radius R1 in a range of 28 to 50 microns, a refractive index profile of a parabola shape with ? being in a range of 1.9 to 2.2, and a maximum relative refractive index difference ?1% max being in a range of 1.9% to 2.5%. The cladding includes an inner cladding and/or a trench cladding, and an outer cladding disposed from the inner to the outer in sequence. The radius R2 of the inner cladding is in a range of 28 to 55 microns, and the relative refractive index difference ?2% is ?0.1% to 0.1%. The radius R3 of the trench cladding is in a range of 28 to 60 microns, and the relative refractive index difference ?3% is in a range of ?0.15% to ?0.8%.

Abstract: A bending-resistant large core diameter high numerical aperture multimode fiber includes a core and a cladding surrounding the core. The core has a radius R1 in a range of 28 to 50 microns, a refractive index profile of a parabola shape with ? being in a range of 1.9 to 2.2, and a maximum relative refractive index difference ?1% max being in a range of 1.9% to 2.5%. The cladding includes an inner cladding and/or a trench cladding, and an outer cladding disposed from the inner to the outer in sequence. The radius R2 of the inner cladding is in a range of 28 to 55 microns, and the relative refractive index difference ?2% is ?0.1% to 0.1%. The radius R3 of the trench cladding is in a range of 28 to 60 microns, and the relative refractive index difference ?3% is in a range of ?0.15% to ?0.8%.

Abstract: The invention relates to a method for manufacturing low PMD single-mode fiber and a fiber manufactured by said method. The twisting system is mounted at the downstream side of a normal fiber-drawing tower. The manner of twisting does not change the fiber-drawing path, the axis of twisting wheels periodically swing in a plane which is parallel to the fiber-drawing direction. The fiber moving at high speed makes the outer surfaces of the twisting wheels to rotate round the axis of the fiber, when an angle between the plane in which the twisting wheels are located and the fiber-drawing direction exists, the component of the angular velocity in the radial direction of the fiber reacts on the fiber and makes the fiber to twist, and the twist propagates to the soften region of the glass material at the fiber-drawing upstream in the form of mechanical wave, a plastic deformation is produced and set up in the newly drawn fiber.