While optical fibers display excellent performances in the infrared, visible and ultraviolet ranges remain poorly addressed by them. Obtaining better fibers for the short-wavelength range has been restricted, in all fiber optics, by scattering processes. In hollow-core fibers, the scattering loss arises from the core roughness and represents the limiting factor for loss reduction regardless of the cladding confinement power. Here, we report on the reduction of the core surface roughness of hollow-core fibers by modifying their fabrication technique. The effect of the modified process has been quantified and the results showed a root-mean-square surface roughness reduction from 0.40 to 0.15 nm. The improvement in the core surface entailed fibers with ultralow loss at short wavelengths. The results reveal this approach as a promising path for the development of hollow-core fibers with loss that can potentially be orders of magnitude lower than the ones achievable with silica-core counterparts.

<p>This is the pre-review draft of the first of two papers submitted to Journal of Lightwave Technology, where we propose and apply a methodology for the analysis of the loss in tube lattice fibers (TLFs) based on the azimuthal Fourier decomposition (AFD) of the fiber’s modes along the perimeters of the tubes composing the fiber cladding. This technique combined with the coupled mode theory constitutes an effective approach for gaining insight in the waveguiding mechanism and for additional loss analysis due to fiber non-idealities. In this part I we describe the approach and apply it to loss analysis of ideal TLFs. The approach is then applied to the analysis of tube thickness variation effects in the part II.</p>

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