11 FIG. 1: (a) Schematic of the coupled waveguide system com- posed by two equal single-mode channel waveguides W$_{1}$ and W$_{2}$ side-coupled to a slab waveguide S. (b) The quantum mechanical analogue, showing the decay of two bound states coupled to a common continuum. (a) y x z W W$^{1}$ 2 S d d W$_{1}$ W$_{2}$ S continuum energy (b) a