Efficient coupling of light between single-mode waveguides and supercollimating photonic crystals

We study the coupling of light between strip and rib waveguides and supercollimating photonic crystals on silicon-on-insulator substrates. The dispersive properties of the supercollimating photonic crystal are used to define the design requirements on the excitation waveguide and the boundary of the photonic crystal is optimized to improve the impedance matching between the two structures. By 3D calculations, we find that rib waveguides can yield transmission efficiencies up to about 96 % and reflections lower than 0.2 % at wavelengths close to 1.55 pm, while insuring single-mode propagation. This work therefore constitutes an important step toward the integration of supercollimation- based optical circuits on photonic chips.