Geometric filterless photodetectors for mid-infrared spin light

Free-space circularly polarized light (CPL) detection, requiring polarizers and wave plates, is well established, but such a spatial degree of freedom is unfortunately absent in integrated on-chip optoelectronics. The filterless CPL photodetectors reported so far suffer from an intrinsic small discrimination ratio, vulnerability to the non-CPL field components and low responsivity. Here we report a distinct paradigm of geometric photodetectors in the mid-infrared, exhibiting a substantial discrimination ratio of 84, a close-to-perfect CPL-specific response, a zero-bias responsivity of 392 V W−1 at room temperature and a detectivity of ellipticity down to 0.03° Hz−1/2. Our approach makes use of a plasmonic nanostructures array with judiciously designed symmetry, assisted by graphene ribbons, to electrically read their near-field optical information. This geometry-empowered recipe for infrared photodetectors provides a robust, direct, strict and high-quality solution to on-chip filterless CPL detection and unlocks new opportunities for integrated functional optoelectronic devices.