Control of heating in active doped optical fiber

A method of thermally drawing a fiber preform into a length of optical fiber including a fiber core, an inner cladding layer, and an outer cladding layer, comprising:

• arranging said fiber preform including a fiber preform core material;
• a fiber preform inner cladding layer material, and a fiber preform outer cladding layer material;
• feeding said fiber preform through a thermal furnace of an optical fiber draw tower to draw the fiber preform into said length of optical fiber having a fiber core, an inner cladding layer, and an outer cladding layer;
• and
• feeding said length of thermally drawn optical fiber through fiber shaping hardware disposed downstream of said thermal furnace of said optical fiber draw tower;
• controlling said fiber shaping hardware with fiber shaping control electronics to produce along said length of optical fiber at least one low-absorption fiber section having a first cross-sectional geometry of the inner cladding layer corresponding to a first level of absorption of input pump light from the inner cladding layer to the fiber core, and to produce along said length of optical fiber at least one high-absorption fiber section having a second cross-sectional geometry of the inner cladding layer corresponding to a second level of absorption of input pump light from the inner cladding layer to the fiber core that is greater than said first level of absorption of input pump light;
• and
• pulling said fiber preform into and through the thermal furnace and the fiber shaping hardware by a fiber draw tower tractor disposed downstream of the shaping hardware.