Diatomic metasurface based broadband J-plate for arbitrary spin-to-orbital conversion

Conventional optical elements to realize spin-to-orbital angular momentum conversion of light can only allow conversion of opposite spin angular momentum (SAM) states into opposite orbital angular momentum (OAM) states. This limitation was recently broken by a metasurface based J-plate with combined geometric and propagation phase design that can convert arbitrary SAM into angular momentum states with independent OAM. However, the intrinsic dispersive nature of the propagation phase restricts its bandwidth to a specific wavelength. Here, we demonstrate a J-plate that can realize arbitrary spin-to-orbital angular momentum conversion in a broad bandwidth from 650 nm to 900 nm. This is achieved through a novel diatomic metasurface design by combining the geometric phase and detour phase, both of which are completely decoupled from the spectral response of meta-atoms and thus intrinsic broadband. The demonstration of broadband arbitrary spin–orbit-conversion and vector vortex beams by such J-plate significantly opens new routes for high-performance spin-orbital interaction of light.