Abstract

We present a new design for beam splitting components employing a silicon-on-insulator rib waveguide structures. In the new design, a high-index thin-film layer is deposited in the rib section to reduce the wave field dispersive tails in the slab section and accordingly render the mode field a confined spot. This in turn improves the beam splitting performance of some conventional waveguide components such as y branches and multimode interference couplers (MMICs), in terms of the excess loss, fiber coupling loss, and compactness of these components. For a $1\times 2$ y-branch beam splitter, the excess loss can be as small as $0.43\mathrm{dB}$ in the new design, which is much lower than that for a conventional rib waveguide structure (which is $1.28\mathrm{dB}$). For a $1\times 2$ MMIC in our example, the new rib waveguide structure presents an excess loss of $0.064\mathrm{dB}$ for the TE mode and $0.046\mathrm{dB}$ for the TM mode, with negligible nonuniformity in dimensions of $30\mu \mathrm{m}\times 1040\mu \mathrm{m}$, whereas its counterpart (i.e., the one with the same dimensions but without a thin-film layer) presents an excess loss of $\sim 0.86\mathrm{dB}$ for both modes. A conventional MMIC must have dimensions larger than $70\mu \mathrm{m}\times 5650\mu \mathrm{m}$ to maintain almost the same low excess loss.

© 2005 Optical Society of America

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