We report on the successful demonstration of a single-mode polymer-optical fiber with an 8-mu m-diameter nonlinear-optical core composed of a dye-chromophore-doped polymer. Both solid-solution cores and copolymer cores were successfully fabriated. Using an imaging system, we show that the far-field transverse light pattern is that of a single-mode guide. We find that the loss at 1064 nm for the single-mode fiber is approximately 0.2 dB/cm and that it preserves polarization to better than 99.8% cm. (C) 1996 Optical Society of America.