Collapsing a multitube assembly and subsequent optical fiber drawing in the same furnace

A method of making an optical fiber, comprising the steps of:

• providing a preform core rod;
• positioning a first overclad tube around the preform core rod;
• positioning at least one second overclad tube around the first overclad tube;
• establishing a pressure gradient across the exterior and the interior of at least the second overclad tube, wherein the pressure outside the second overclad tube is greater than the pressure inside the second overclad tube;
• heating the preform core rod, the first overclad tube and the at least one second overclad tube wherein the first overclad tube collapses onto the preform core rod and the second overclad tube collapses on the first overclad tube to form a multiple overclad optical fiber preform;
• and
• drawing the optical fiber from the overclad optical fiber preform
• wherein the heating step and the drawing step are performed using the same heat source.