Four-ray interference model for complete characterization of tubular anti-resonant hollow-core fibers.

We propose a comprehensive four-ray interference model based on simple geometric optics that can be employed to characterize all the structural parameters of an anti-resonant hollow-core fiber with tubular cladding structures in a non-invasive and fast way. Combining this model with white-light side-scattering spectroscopy, the outer and the inner radii of the jacket tube can be measured with sub-micron accuracy. The improved illumination source and collimator enable fast spectrum acquisition and identification of the key interference peaks of the four rays. A fitting-based estimate of the interference peaks fully exploits a wealth of spectra acquired at different rotation angles and can help to retrieve the diameter of the cladding tubes with high resolution of 0.17 µm, which exceeds the diffraction limit of the probe light. We also report for the first time, to the best of our knowledge, the polarization and the transverse mode dependences in the side-scattering interference spectra, with which the glass wall thicknesses of the cladding tubes can be estimated on the basis of our four-ray interference model as well.