Highly multi-mode hollow core fibers.

The loss and damage thresholds of conventional solid core fibers are greatly improved in anti-resonant hollow core fibers, but fabrication has largely been limited to single mode hollow fibers. There are many applications of conventional multi-mode fibers that would also benefit from the properties of hollow core fibers and are not currently addressed. This is particularly important at ultraviolet and mid-infrared wavelengths where single-mode lasers are harder to obtain and other light sources are commonly less bright than in the visible and near infrared, requiring multi-mode optical fibers for efficient delivery of the light. We report the design and fabrication of multi-mode hollow core fibers, guiding at least 50 spatial modes in the near-infrared while retaining low propagation losses and reasonable bend losses despite core radii greater than 60 times the guided wavelengths. We demonstrate our design approach from ultraviolet to mid-infrared light, enabling the guidance of ∼ 20 - 30 spatial modes at 340 nm or 3 µm within octave spanning bandwidths. 3 multi-mode fibers are sufficient to cover the entire wavelength range from 200 nm to 4 µm.