Integrated optical beam splitters employing symmetric mode mixing in SiO₂/SiON/SiO₂ multimode interference waveguides

A collection of SiON films with different chemical compositions (various O/N ratios) were deposited on silicon substrates using plasma-enhanced chemical vapor deposition (PECVD). These films were then optically characterized to delineate the impacts of relevant film growth parameters to the corresponding refractive indices and infrared absorption spectra. The refractive indices of SiON films with different O/N ratios spanned from 1.47 to 1.93 were realized by judiciously adjusting the pertinent PECVD gas flow rates. Next, the integrated 1-to-8 and 1-to-16 multimode interference (MMI) power beam splitters were designed and fabricated based on the numerical simulation using beam propagation method (BPM). The normalized light intensities varied from ∼0.92 to 1 and from ∼0.88 to 1 for symmetrical 1 × 8 and 1 × 16 devices, which correspond to the maximum power imbalances of 0.38 and 0.56 dB, respectively. Finally, the ramification of varying the width of multimode waveguide section was also investigated numerically using BPM tecnnique.