Metasurfaces-based polarisation imaging systems for small form-factor satellites

Full-Stokes polarimetric imaging enhances the information available from satellite remote sensing. But the numerous bulky and heavy optical components required to achieve polarimetric imaging limit its use for small-form satellites. We present the modelling of an ultra-thin nanostructured metasurface as a novel solution to the weight and volume constraints faced by small satellites. Positioned in a telescope's pupil plane, the metasurface diffracts light into five polarization measurements that are imaged onto a detector, restoring the full field of view as the satellite moves over the Earth's surface. Designed to have effective redundancy, any four out of the five orders enable the reconstruction of the full polarization state, allowing error monitoring. The metasurface material is 1 μm thick silicon repeating patterns on a 460 μm thick sapphire substrate, utilising free-form topology to optimise for throughput efficiency and equal light distribution between the polarization diffraction orders.