Freezing of the transmitted wave pattern through gratings

In wave transport through complex media, the single-channel regime is characterized by the loss of sensitivity to incidence conditions, resulting in an invariant pattern of the transmitted wave. So far, such “frozen” patterns have been observed in localized disordered media and in periodic waveguides. In this paper, we show that the same mechanism can occur in the transmission through gratings when properly designed, allowing the observation of the freezing when an incident plane wave is scattered by a grating composed of two successive arrays of scatterers: one mixing the incident orders in arbitrary ways, followed by a freezing array periodically structured in the longitudinal direction, normal to the grating plane. Unlike localized disordered media, where freezing occurs only with evanescent waves, gratings, similarly to periodic waveguides, can exhibit freezing with propagating waves when a single Bloch mode is propagating in the longitudinal direction. Moreover, we show different classes of grating geometries for which the occurrence of freezing is sensitive or insensitive to the incidence angle.