Top-Hat Beam Shaping via Asymmetric Hollow-Core Anti-Resonant Fibers

Abstract

Conventional low-loss Hollow-Core Anti-Resonant Fibers (ARFs) deliver a near-Gaussian fundamental mode profile that is suboptimal for applications favoring uniform irradiance. We show here that deliberately breaking the cladding symmetry can allow for delivering a low-loss fundamental mode with a top-hat intensity profile, with no need for mode mixing or external beam-shaping optics. By enlarging one pair of nested cladding capillaries relative to the orthogonal pair, the core is elongated and the y-polarized fundamental mode reshapes from a near-Gaussian distribution into a flat-top profile whose 90%-intensity plateau width is 104.8% wider than that of a symmetric reference fiber at λ=1μm. Full-vectorial simulations show that this plateau varies by less than 2.1% across the 900–1600 nm near-infrared guidance band, where the confinement loss falls below 1 dB/km, and that the shaping mechanism persists essentially unchanged from the visible to the mid-infrared, where the overall attenuation remains below 0.1 dB/m within the 2700–3200 nm wavelength range. These results establish a purely geometric route to broadband top-hat beam delivery in anti-resonant hollow-core fibers.