Polyethersulfone (PES) optical fibers are drawn and thermally processed in order to generate variable side-illumination profiles. The thermal treatment allows microbubbles to be formed in an outer layer of the PES fiber, providing light scattering with controllable amplitudes (0.25-2.5 cm-1). Several fibers with different scattering profiles, such as uniform axial irradiation and multiple irradiation spots, are demonstrated. A small microbubble-induced scattering spot on the surface may be used for side-coupling of ambient light into the fiber. These mechanically flexible all-PES fibers with custom-designable scattering profiles may be useful for spatially tuned delivery of light for various applications, including phototherapy.