Optical fiber with inverse triangular trench design

A method of making a single mode optical fiber, the method comprising:

• providing an overclad assembly that forms a hollow central channel;
• inserting a consolidated core assembly into the hollow central channel to form a core-cladding assembly such that a gap is disposed between the consolidated core assembly and the overclad assembly;
• heating the core-cladding assembly to collapse the overclad assembly on the consolidated core assembly to form a single mode optical fiber preform, and
• while heating the core-cladding assembly, flowing a down-dopant precursor into the gap to provide a depressed-cladding index region in a cladding region of the single mold optical fiber drawn from the single mode optical fiber preform,
• wherein:
• a relative refractive index Δ3 of the depressed-index cladding region increases with increased radial position, and
• the depressed-index cladding region comprises a volume V3a, which is defined by a first radial position at an inner radius of the depressed-index cladding region and a second radial position at 20 microns, in a range of about 20.0% Δ-micron2 to about 70.0% Δ-micron2.