A low loss graded index polymer optical fiber (GI POF) with a wide wavelength range around 650 nm is fabricated using a copolymer of methyl methacrylate and pentafluorophenyl methacrylate as a polymer matrix. Dopant hydrophobicity similar to that of the polymer matrix is an important factor in maintaining the low loss of the GI POF. No loss increment is observed under damp heat conditions of 75°C and 85% relative humidity when using 9-bromo phenanthrene as the high refractive index dopant required to form the GI profile. The copolymer based GI POF can provide an inexpensive premise network with long-term stability.