High‐Contrast Switching of Light Enabled by Zero Diffraction

Diffraction allows to change the direction of light. Therefore, controlling diffraction efficiency with high contrast enables pathway light within optical systems. However, a requires that is tunable close zero. Probably most prominent example for zero in waveguide grating bound state continuum (BIC). Herein, two plane waves under symmetric incidence leaky found. The phenomenon not only occurs at singular spectral positions but on continuous curves energy–momentum space. relative phase large control over wide range. practical meaning this finding local switching demonstrated. Light trapped into nonlinear and detrapped desired position electric control. A exceeding 1000 experimentally shown.