As-Grown Miniaturized True Zero-Order Waveplates Based on Low-Dimensional Ferrocene Crystals.

As basic optical elements, waveplates with anisotropic electromagnetic responses are imperative for manipulating light polarization. Conventional waveplates are manufactured from bulk crystals (e.g., quartz and calcite) through a series of precision cutting and grinding steps, which typically result in large size, low yield, and high cost. In this study, a bottom-up method is used to grow ferrocene crystals with large anisotropy to demonstrate self-assembled ultrathin true zero-order waveplates without additional machining processing, which is particularly suited for nanophotonic integration. The van der Waals ferrocene crystals exhibit high birefringence (Δn (experiment) = 0.149  ±  0.002 at 636 nm), low dichroism Δκ (experiment) = -0.0007 at 636 nm), and a potentially broad operating range (550 nm to 20 µm) as suggested by Density Functional Theory (DFT) calculations. In addition, the grown waveplate's highest and the lowest principal axes (n and n , respectively) are in the a-c plane, where the fast axis is along one natural edge of the ferrocene crystal, rendering them readily usable. The as-grown, wavelength-scale-thick waveplate allows the development of further miniaturized systems via tandem integration.