When optical fibers are prepared by the (CVD) technique, an index dip often appears at the core center. The index dip reduces the coupling efficiency to optical sources and also it reduces the transmission bandwidth. This index dip in the core with germania‐doped silica could be eliminated successfully with a flow of the vapors of controlled proportion of GeCl4and O2during the collapse. The graded‐index fibers without dip were prepared by this technique. The bandwidth was increased from 500 to 800 MHz : km and the coupling efficiency by 20% when the index profile was controlled and the index dip was eliminated.