Metasurface optics for on-demand polarization transformations along the optical path

Using a metasurface that allows shaping of the polarization state of a light beam independently at each point of space along its propagation direction, longitudinally variable polarization optical components are demonstrated, inspiring new directions in structured light, polarization-switchable devices and light-matter interaction. Polarization plays a key role in science; hence its versatile manipulation is crucial. Existing polarization optics, however, can only manipulate polarization in a single transverse plane. Here we demonstrate a new class of polarizers and wave plates-based on metasurfaces-that can impart an arbitrarily chosen polarization response along the propagation direction, regardless of the incident polarization. The underlying mechanism relies on transforming an incident waveform into an ensemble of pencil-like beams with different polarization states that beat along the optical axis thereby changing the resulting polarization at will, locally, as light propagates. Remarkably, using form-birefringent metasurfaces in combination with matrix-based holography enables the desired propagation-dependent polarization response to be enacted without a priori knowledge of the incident polarization-a behaviour that would require three polarization-sensitive holograms if implemented otherwise. Our work expands the use of polarization in the design of multifunctional metasurfaces and may find application in tunable structured light, optically switchable devices and versatile light-matter interactions.

Automated summary

By using metasurfaces to independently shape the polarization state of a light beam at each point in space along its propagation direction, longitudinally variable polarization optical components are demonstrated; a new class of polarizers and wave plates based on metasurfaces can impart an arbitrarily chosen polarization response along the propagation direction, regardless of the incident polarization; this approach allows for the desired propagation-dependent polarization response to be enacted without prior knowledge of the incident polarization, expanding the use of polarization in the design of multifunctional metasurfaces.