Theoretical bend loss for the 3D bent step-index optical fiber

Determine the theoretical bend loss for a three-dimensional circularly coiled step-index optical fiber, quantified by the decay of optical power per unit arc length or an equivalent imaginary part of an effective propagation constant, when the fiber is excited by the LP02 mode of the corresponding straight fiber and subject to perfectly matched layer absorbing conditions in the circumferential and radial directions.

Background

The authors compute and validate bend-loss exponents for two-dimensional bent slab waveguides against semi-analytic eigenvalue results, but note that such semi-analytic solutions are not available for the three-dimensional coiled fiber geometry.

In the 3D fiber experiment, they therefore report simulated power decay but explicitly state that the corresponding theoretical bend loss is not known.