Hollow-core preforms and hollow-core optical fibers and methods of making the same

A hollow-core preform, comprising:

• a preform longitudinal axis;
• an outer tube disposed around the preform longitudinal axis, the outer tube comprising:
• an inner surface defining an interior cavity through which the preform longitudinal axis extends;
• an outer surface;
• and
• a thickness defined by a distance between the inner surface and the outer surface that is greater than or equal to 2 mm and less than or equal to 15 mm;
• an inner tube disposed inside the interior cavity of the outer tube, the inner tube comprising:
• an inner tube longitudinal axis offset from the preform longitudinal axis;
• an inner surface disposed around the inner tube longitudinal axis;
• an outer surface;
• a thickness defined by a distance between the inner surface and the outer surface that is greater than or equal to 0.5 mm and less than or equal to 10 mm;
• a first end;
• a second end opposite the first end;
• and
• a length extending between the first end and the second end;
• wherein the outer surface of the inner tube is bonded directly to the inner surface of the outer tube continuously along a majority of the length of the inner tube;
• and
• wherein a distance between the inner surface of the inner tube and the outer surface of the outer tube at the location of bonding substantially corresponds to the thickness of the inner tube and the thickness of the outer tube combined.

A method of making a hollow-core preform, comprising:

• providing an outer tube, wherein the outer tube comprises:
• an outer tube longitudinal axis;
• an inner surface defining an interior cavity through which the outer tube longitudinal axis extends;
• an outer surface;
• and
• a thickness defined by a distance between the inner surface and the outer surface;
• positioning an inner tube inside the interior cavity of the outer tube, wherein the inner tube comprises:
• a first end;
• a second end opposite the first end;
• a length between the first end and the second end;
• an inner tube longitudinal axis extending from the first end to the second end and offset from the outer tube longitudinal axis;
• an inner surface disposed around the inner tube longitudinal axis;
• an outer surface;
• and
• a thickness defined by a distance between the inner surface and the outer surface;
• flowing one or more glass precursors into the interior cavity of the outer tube;
• heating the outer tube to cause the one or more glass precursors to form soot particles on at least one of the outer surface of the inner tube or the inner surface of the outer tube.