In polarimetry, that is, a measurement of the four-component polarization Stokes vector, a measurement must either consist of four (or more) sequential intensity measurements, sacrificing time resolution, or contain four separate light paths each with separate polarization optics, increasing bulk, cost, and system complexity. Similar issues present difficulty across polarization optics technology.
Metasurfaces, nanophotonic arrays of phase shifting elements, have emerged as a novel platform for polarization optics. These individual phase shifters can be designed with a characteristic anisotropy, and are thus imbued with tunable shape birefringence. A metasurface, then, can function as a subwavelength spaced array of nanoscale waveplates.
I will describe how, through relatively simple optimization methods, a metasurface producing arbitrarily specified polarization states (when illuminated with light of a known polarization) can be designed. This functionality is equivalent to a traditional diffraction grating with individual waveplate optics on each order; here, all the necessary polarization optics can be integrated into a flat, ultrathin optical element. Moreover, such a metasurface can be used in a reverse configuration as a parallel snapshot polarimeter with no need for additional polarization optics (save for a single polarizer). I present a detailed experimental characterization of both concepts in the visible spectral region and a comparison of the performance of the metasurface to a commercially available rotating waveplate polarimeter. With no bulk birefringent crystal optics, a parallel, full-polarization state measurement can be made with an integrated, scalable, and inexpensive device. Given its diffractive nature, the design naturally extends to spectropolarimetry and polarization imaging.