We present wideband nonpolarizing beam splitters (NPBSs) for the telecommunication C-band. We show that silicon-on-insulator subwavelength periodic elements operating near leaky-mode resonance provide useful spectral expressions enabling effective beam division. Particle swarm optimization is the design method of choice. Periodic single-layer and multilevel NPBSs are provided exhibiting 50/50 beam ratio under oblique and normal incidence. We compare the spectral performance of the beam splitters with that of their thin-film effective-medium counterparts, thereby verifying the resonancemediated origin of the spectra sought. The beam splitters are found to be reasonably tolerant to deviations in angle of incidence and structural parameters.

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