Hollow-core optical fiber with single nested capillaries exhibiting improved confinement loss

A hollow-core optical fiber comprising:

• a substrate that is tubular comprising an inner surface surrounding a central longitudinal axis of the hollow-core optical fiber;
• and
• a plurality of cladding elements spaced apart from each other and disposed within the substrate, the plurality of cladding elements together defining a hollow-core region surrounding the central longitudinal axis of the hollow-core optical fiber with the plurality of cladding elements disposed radially between the substrate and the hollow-core region, each of the plurality of cladding elements extending parallel to the central longitudinal axis, and each of the plurality of cladding elements comprising:
• a first capillary that is tubular comprising (i) an outer surface having an outer diameter and contacting the inner surface of the substrate at a first contact region and (ii) an inner surface defining a first cavity with a first longitudinal axis parallel to the central longitudinal axis, and
• a second capillary that is tubular disposed within the first cavity defined by the first capillary, the second capillary comprising (i) an outer surface having an outer diameter and contacting the inner surface of the first capillary at a second contact region and (ii) an inner surface defining a second cavity with a second longitudinal axis parallel to the central longitudinal axis,
• wherein, for each of the plurality of cladding elements, a first line extends orthogonally from the central longitudinal axis through the first longitudinal axis and the first contact region,
• wherein, for each of the plurality of cladding elements, a second line extends through the second longitudinal axis, the second contact region, and the first longitudinal axis,
• wherein, for each of the plurality of cladding elements, the first line and the second line are separated by an angle that is within a range of from 20 degrees to 120 degrees,
• wherein, for each of the plurality of cladding elements, a ratio of the outer diameter of the second capillary to the outer diameter of the first capillary is within a range of from 0.47 to 0.85, and
• wherein, the plurality of cladding elements numbers within a range of from 5 to 8.