Metasurface Diffraction Gratings for Arbitrary Polarization State Generation and Measurement

Abstract

Metasurfaces, nano-structured arrays of phase-shifting elements, can sample phase functions at sub-wavelength scales. These novel devices hold the potential to replace bulky, conventional optics with ultra-thin devices with thicknesses on the order of just a few microns. In this project, we have used metasurfaces to implement polarization generation diffraction gratings, which are designed to produce desired polarization states in desired diffraction orders, when 45º polarized light is incident on the grating. The project describes in detail how to design and optimize phase profiles to generate arbitrary polarizations in chosen diffraction orders, to be implemented using discrete dielectric metasurface elements (TiO2 nanopillars). The optimized designs are fabricated, and the generated polarization states experimentally verified, to show good agreement with theory and simulations. Furthermore, we also demonstrate how the metasurface polarization generation diffraction grating can be designed and used as a single-shot polarimeter, after proper calibration. Our metasurface polarimetry results for measuring the degree of polarization (DOP), and the state of polarization (SOP) have been found to be accurate, on average, within 5% with the potential for further enhancement with simple improvements in the optical measurement setup. The metasurface polarimeter is also experimentally shown to be capable of measuring partial polarization (DOP<1). The proposed design of polarization generation diffraction gratings, and its implementation with ultra-thin metasurfaces can be useful in current and future compact polarization optics and sensing applications, including polarization imaging.