Optimization of the cladding structure to minimize surface roughness scattering in antiresonant, hollow-core fibers

Scattering from the microscopic roughness of glass-air interfaces that arises from frozen-in surface capillary waves is often the limiting factor in minimization of the propagation loss of hollow-core optical fibers. The strength of this scattering is typically modelled through calculation of the normalized electric field intensity, F, of the core-guided modes at the glass-air interfaces. An alternative formulation of F is proposed that resolves an ambiguity arising from the discontinuity of the normal component of the electric field across each interface. Theoretical analysis of a concentric-layers model of antiresonant, hollow-core fibers, backed up by numerical simulations of realistic fiber designs, shows that, for a given wavelength, F can be minimized by using a core surround of antiresonant thickness and that, to a good approximation, other structural features of the cladding make no significant difference to the value of F.