Optical fiber

An anti-resonant hollow-core optical fiber with a waveguide structure having a longitudinal direction. The optical fiber comprises an outer cladding region extending in the longitudinal direction, the outer cladding region having a substantially tubular inner wall forming an internal volume, and a core region comprising a central void. The fiber further comprising an inner cladding region comprising an optical material, the inner cladding region being arranged around the core region within the internal volume and extending in the longitudinal direction, the inner cladding region comprising a plurality of anti-resonance elements being arranged adjacent to the inner wall, each having an elongated cross-sectional geometry with a minor axis and a major axis, wherein the major axis is arranged along a radial direction of the fiber and the minor axis is arranged along a tangential direction of the fiber, and wherein the anti-resonance elements are further arranged in a distance from their neighboring elements, and wherein the anti-resonance elements have a negative curvature where they are proximal to the core region.