Geometrical factor modification of helical-core fiber radiation loss formula

A strict consideration of the geometry of helical-core fibers leads to a modification of a previously published formula for radiation loss in such fibers. We derive an expression for the radiation loss of the fundamental mode, and find that it differs from the previous expression by a simple modification factor, which depends on the geometric parameters of the helix (pitch and offset). The derived expression predicts a loss which is of the order of 40% lower for typical helix parameters