Even though submicron silicon waveguides have been proposed for dense
integration of photonic devices, to date the lightwave circuits on the market
mainly rely on waveguides with micron-scale core dimensions. These larger
waveguides feature easier fabrication, higher reliability and better
interfacing to optical fibres. Single-mode operation with large core dimensions
is obtained with low lateral refractive index contrast. Hence, the main
limitation in increasing the level of integration and in reducing the cost of
micron-scale waveguide circuits is their mm- to cm-scale minimum bending
radius. Fortunately, single-mode rib waveguides with a micron-scale silicon
core can be locally transformed into multi-mode strip waveguides that have very
high lateral index contrast. Here we show how Euler spiral bends realized with
these waveguides can have bending radii below 10 {\mu}m and losses below 0.02
dB/90{\deg} for the fundamental mode, paving way for a novel densely integrated
platform based on micron-scale waveguides.Comment: 14 pages, 29 Refs., 5 Fig
