Method for making large diameter multicore optical waveguide

A method for making a multicore optical waveguide having an outer diameter of at least about 0.3 millimeters, two or more inner cores, and a cladding surrounding the two or more inner cores, comprising:

• assembling a preform assembly for drawing the multicore optical waveguide, wherein the assembling comprises:
• providing an outer tube having a cross-section of at least about 0.3 millimeters;
• notching the outer tube with two or more notches, wherein at least one of the notches is disposed in an outer surface of the outer tube;
• and
• arranging two or more preform elements in relation to the outer tube, wherein the two or more preform elements yield the two or more inner cores and wherein the arranging comprises providing a respective one of the preform elements in each notch;
• heating the preform assembly;
• and
• drawing the optical waveguide from the preform assembly, thereby defining the outer diameter that is at least about 0.3 millimeters upon completion of the drawing, and thereby leaving in an area of the optical waveguide that has been drawn a longitudinal aperture extending through the optical waveguide.