In a draw tower for producing a length of optical fiber, a preform feed accepts a preform into the draw tower and a furnace downstream of the preform feed heats the preform. Fiber shaping hardware downstream of the thermal furnace is controlled by fiber shaping control electronics to produce along the 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 core and 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 core that is greater than the first level of absorption. A tractor downstream of shaping hardware pulls the preform through the furnace and shaping hardware.