Preform for producing vortex fiber

A preform for making a vortex optical fiber, comprising:

• a single glass cylinder formed substantially of silicon dioxide that defines a core portion having a first index of refraction value along a longitudinal axis of the single glass cylinder and a cladding portion having a second index of refraction value surrounding the core portion;
• wherein the single glass cylinder further defines a first hole along the longitudinal axis from a first end of the single glass cylinder to a second end of the single glass cylinder completely through the core portion of the single glass cylinder and a plurality of second holes running parallel to the longitudinal axis from the first end of the single glass cylinder to the second end of the single glass cylinder completely through the cladding portion of the single glass cylinder, the first hole only comprising a part of the core portion of the preform;
• wherein the preform defines a refractive index profile that contains a valley along the longitudinal axis of the single glass cylinder and a pair of peaks along edges of the core portion with the cladding portion;
• wherein the refractive index profile steadily decreasing from one of the pair of peaks to the valley and steadily increasing from the valley to a second one of the pair of peaks;
• and
• wherein the refractive index profile is established by the first hole and the plurality of second holes rather than by doping of the core portion and the cladding portion of the single glass cylinder.

A preform for making a vortex optical fiber includes a single glass cylinder formed substantially of silicon dioxide that defines a core portion of a first diameter having a first index of refraction value along a longitudinal axis of the single glass cylinder and a cladding portion having a second index of refraction value surrounding the core portion, the single glass cylinder further defines a first hole having a second diameter smaller than the first diameter along the longitudinal axis from a first end of the single glass cylinder to a second end of the single glass cylinder completely through the core portion of the single glass cylinder and a plurality of second holes running parallel to the longitudinal axis from the first end of the single glass cylinder to the second end of the single glass cylinder through the cladding portion of the single glass cylinder, wherein an index of refraction profile is defined by the first hole and the plurality of second holes rather than by doping of the core portion and the cladding portion of the single glass cylinder, the index of refraction profile containing a valley along the longitudinal axis of the single glass cylinder and a pair of peaks along edges of the core portion with the cladding portion, the index of refraction profile steadily decreasing from one of the pair of peaks to the valley and steadily increasing from the valley to a second one of the pair of peaks, further wherein the single glass cylinder defining the plurality of second holes enables the vortex optical fiber generated from the preform to support propagation of optical signals including orthogonal functions.