Projection of phase singularities in moire fringe onto a light field

A moire pattern, which is a kind of spatial interference between two periodic patterns, is regarded as a spatial modulation of a "field." By defining the displacement field, we reveal that moire patterns can have a topological phase singularity, similar to a disclination in liquid crystal and, more generally, a vector field treated in the singular optics. We propose that topological singularities in the moire displacement field can be projected by passing an electromagnetic field through a metasurface. We designed a metasurface constructed from two layers of a metal disk array operating in the terahertz band; then we numerically estimated the spatial distribution of its transmission properties. The phase singularities in the electromagnetic fields coincided with the singularities appearing in the moire pattern. We found two kinds of singularities, and the phase of the electromagnetic field changed by 2 pi or 4 pi around them. These phase changes were independent of the light frequency, implying that the topological properties of the moire fields were projected onto the electromagnetic field. This feature of moire metasurfaces can potentially be exploited in spiral phase plate arrays with no frequency dispersion of the phase change. Published by AIP Publishing.