Maximal circular polarization isolation and asymmetric polarization conversion by chiral meta-structure

Chiral objects hold immense significance in modern optical technology, particularly due to their ability to manipulate circularly polarized waves. The chiroptical effects observed in naturally known chiral structures are typically very weak, however, the use of engineered meta-structures has proven to be highly effective in overcoming these shortcomings. Despite extensive research efforts, the construction of chiroptical phenomena approaching maximum performance has proven to be challenging, mostly due to the lack of optimal design choices and the existence of material losses. Here we present a metasurface constituting S-shaped building blocks capable of realizing virtually maximum chiroptical phenomena. The structure demonstrates nearly full polarization transmission, conversion to an opposite spin state, and reflection of the opposite spin state at a wavelength of 1549 nm. As a result, the maximum circular dichroism (CD) value reaches up to ≈1 (0.9993) for a given polarization state. Furthermore, reduced symmetry enables the one-way flow of a given polarization state resulting in about unity (0.998) asymmetric transmission (AT) value. Through rigorous numerical simulations, we elucidate the underlying principles driving these extraordinary optical properties. The CD and AT values are record-high demonstrated so far. The single-layer design offers an ultrathin profile, making it compatible with integrated photonics and providing opportunities for applications in compact, lightweight optical devices such as circular polarizers, half-wave plates, and self-polarizing reflectors.