Beam-Size-Invariant Spectropolarimeters Using Gap-Plasmon Metasurfaces

Metasurfaces enable exceptional control over the light with surface-confined planar components, offering the fascinating possibility of very dense integration and miniaturization in photonics. Here, we design, fabricate, and experimentally demonstrate chip-size plasmonic spectropolarimeters, consisting of three gap-plasmon phase-gradient metasurfaces that occupy 120° circular sectors each, for simultaneous polarization state and wavelength determination. The spectropolarimeters diffract normally incident light to six predesigned directions, whose polar angles are proportional to the light wavelength, while contrasts in the corresponding diffraction intensities provide a direct measure of the incident polarization state through retrieval of the associated Stokes parameters. The proof-of-concept 96-μm-diameter spectropolarimeter operating in the wavelength range of 750–950 nm exhibits the expected polarization selectivity and high angular dispersion (0.0133°/nm for the |x⟩ channel). Moreover, we show that, due to the circular-sector design, polarization analysis can be conducted for optical beams of different diameters without prior calibration, demonstrating thereby the beam-size-invariant functionality. The proposed spectropolarimeters are compact, cost-effective, and robust and promise high-performance real-time polarization and spectral measurements.