# Antiresonant Fibers

Antiresonant hollow-core fibers (ARF) guide light in an air core
surrounded by a thin ring of capillary tubes, relying on antiresonant
reflection rather than a photonic bandgap or total internal
reflection. This chapter computes their leaky modes and confinement
loss using finite elements with a frequency-dependent PML, starting
with the basic ARF geometry and then extending to nested antiresonant
nodeless fibers (NANF), which add an inner ring of nested capillaries
to further suppress loss.