The power imbalance between different waveguide outputs is compensated by manipulating the dispersion of the guided propagation in the multimode interference (MMI) region. This is attainable using a tapered region at the beginning of the MMI region that has been verified through simulation and experiment. From this, the fabrication tolerance for the diameters of holes in a tapered $1\times 3$ photonic crystal waveguide (PhCW) splitter is relaxed up to a range of at least $27\mathrm{nm}$ . The output power is well-balanced to within $1\mathrm{dB}$ . The effective bandwidth of the splitters shifts only around $13\mathrm{nm}$ , for a reduction of $10\mathrm{nm}$ in the diameter of the PhCW holes. The optimized component is an outstanding ultracompact $1\times 3$ splitter for the photonic integrated circuit (PIC).