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We show that a controlled intentional mode coupling induced via scattering from core inclusions can substantially improve the bandwidth of graded index multimode fibers with centerline defect. We present a comprehensive analysis of the impact of the dielectric constant, size, density, and location of micrometer size inclusions on the bandwidth and attenuation of these fibers. We show that using a proper design, the bandwidth of a 1-km-long fiber can improve from 693-MHz to more than 2.5-GHz with less than 1-dB additional power loss. We also show that in practice, it is possible to obtain the desired level of mode coupling by exposing the photosensitive core of the fiber to a UV laser, therefore creating the micrometer size inclusions after the draw process.