Spun round core fiber

An optical waveguide, comprising:

• a core that extends along a propagation axis, the core comprising a mode-propagating region and a mode-discriminating region, the mode-propagating region comprising a polygonal cross-section, the mode-discriminating region being disposed around the mode-propagating region such that the mode-discriminating region surrounds the mode-propagating region;
• and
• a cladding disposed about the core and extending along the propagation axis;
• wherein the mode-discriminating region comprises a round outer boundary such that the core has a round cross-section.

A method, comprising:

• machining a silica rod such that the silica rod has a non-circular cross-section, the silica rod having a first index of refraction;
• situating the machined silica rod in a silica tube comprising a second index of refraction different from the first index of refraction;
• and
• collapsing the silica tube to form a core rod preform;
• situating the core rod preform in a cladding tube to obtain an optical waveguide preform;
• and
• drawing the optical waveguide preform to obtain an optical waveguide comprising a core that extends along a propagation axis, the core comprising a mode-propagating region and a plurality of mode-discriminating regions, the mode-propagating region comprising the first index of refraction, the plurality of mode-discriminating regions comprising the second index of refraction, the core comprising a round outer boundary, the optical waveguide comprising a cladding disposed about the outer boundary of the core and extending along the propagation axis, wherein the non-circular cross-section of the mode-propagating region is circumscribed within the outer boundary of the core, and the mode-discriminating regions are defined by the outer boundary of the core and the non-circular cross-section of the mode-propagating region such that the mode-discriminating regions are enclosed by the silica material of the mode-propagating region of the core and the cladding.