Figure 2

(a) Comparison between a standard (S), an abrupt π-shift (A) and a continuous π-shift (C) grating. For the latter the radius of the grating slit center (GSC) is marked. The red and blue grating slits symbolize the π-shifted and unshifted grating elements, respectively. (b) Dual grating above a WGM. The colored light cones couple out the corresponding parts of the WGM. The relative phase shift between the light cones induces destructive interference. Inner and outer waveguide radii are given by W_i and W_o, respectively. G_w denotes the total grating slit width and δ is given by the distance between the GSC and the center of mass (COM) of the WGM.