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A three-dimensional metal-coated semiconductor-quantum-dot (QD) nanoscale lattice structure is designed for optical waveguiding. It is based on three notions: (i) Excitons are first photogenerated in the QDs by the incident electromagnetic field which is the optical wave to be guided: (ii) The exciton-polariton effect in the QD structure induces an extra optical dispersion in the QDs: (iii) The high contrast ratio between the optical dispersions of the QDs and the background material creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained for the incident wave in the lossless case, thus providing the fundamental basis of QDs for optical waveguide applications. Metal coating at the QD surface generates a surface plasmon spatially confined in the QD so that the exciton generation becomes enhanced for a better dielectric modulation.