Metasurfaces and their capability to shape electromagnetic waves open the path to photonic components or devices showing enhanced characteristics compared with traditional embodiments. They may enable an increased compactness, an easier integration or a more practical operation, among other advantages. However, suitable designs need to be found for each targeted application. In this context, Thomas S. Nowack and coworkers have designed, fabricated, and tested a metasurface enabling the measurement of the polarization state of electromagnetic waves at frequencies around 3 THz. The metasurface consists of three interleaved arrays of silicon micro-pillars on a silicon wafer. When illuminated by a collimated beam, the waves it transmits draw an image that consists of an hexagonal pattern, in which the spot intensities depend on the beam's polarization. By capturing this image on a THz camera, and suitably analysing it, the polarization state of the beam can be revealed. This requires knowing the response of the metasurface-camera system, which the authors determined by performing a calibration using reference beams with a known (linear or circular) polarization. After completing this step, they retrieved the Stokes parameters S₁, S₂, and S₃ of an arbitrarily generated beam, with an estimated accuracy of 92%. This work is appealing for THz sensing and testing without rotating photonic components.

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