We proposed a graded-index polymer optical fiber (GI-POF) enabling greater-than-gigabit data transmission in a short reach network by applying a two-step interfacial-gel polymerization process to a perdeuterated polymer material. Using this process, it is possible to fabricate a nearly optimum refractive-index profile with good reproducibility. In this paper, the preparation of a perdeuterated polymethyl methacrylate (PMMA-d8)-based GI-POF utilizing a PMMA cladding is described. This means that the low-loss PMMA-d8 material is used only for the core. Because the cladding transmits only a small fraction of the optical power, a low-loss material is not necessarily required for the cladding. It was verified that the low attenuation of the PMMA-d8 was maintained even if the cladding was composed of hydrogenated PMMA. As a result, a gigabit data transmission over 300 m was achieved by the PMMA-d8-core and PMMA-cladding GI-POF, which was impossible by the conventional PMMA-based GI-POF.