An optical power splitter with one input and three output ports is proposed and demonstrated for near-infrared applications in the wavelength range of 2.3 to 2.5 μm. The device operates on the principle of directional coupling by introducing photonic crystal line-defect waveguides. Its functionality and performance have been numerically investigated and simulated by the finite-difference time-domain method. By cascading two 1 × 3-structure power splitters, a large-scale optical power splitter with one input and five output ports is achieved. The simulated results show that the 1 × 5 large-scale power splitter can also perform 1 × 2, 1 × 3, and 1 × 4 functions. The required optical power from each of the output waveguides can be easily controlled by adjusting the coupling length of interaction for photonic crystal line-defect waveguides. The total length of the 1 × 5 power splitter is 40 μm, which is significantly less than that of the conventional non-photonic-crystal power splitter. This is a promising device for future ultracompact and large-scale nanophotonic integrated circuits. © 2006 Society of Photo-Optical Instrumentation Engineers.