Toward On-Chip Nascent All-van-der-Waals Polarization Optical Elements for Nanoscale Photonic Applications

The integration of polarization-control elements into nanoscale photonic circuits remains a central challenge for modern on-chip optical technologies, which call for continuous miniaturization. Van der Waals (vdW) crystals provide a versatile platform for their creation because of strong optical anisotropy, low loss accompanied by high refractive indices, and atomically precise heterostructure assembly capabilities. In this work, we present an approach towards the creation of all-vdW on-chip birefringent polarization-conversion elements operating in the near-infrared (NIR) spectral region, realized by uniquely twisted $ReS{e}_2/\alpha -Mo{O}_3$ heterostructures placed on a $Si/Si{O}_2$ platform. Our proof-of-principle stacks demonstrate up to 64.5 $\%$ average degree of circular polarization (DoCP) quantitatively reproduced by finite-difference time-domain (FDTD) simulations. The latter reveals critical roles of layer thickness, twist angle, and Fabry-Perot interference effects in the determination of polarization conversion efficiency, which yields DoCP values close to unity for a layer thickness of about twice that of zero-order quarter-wave plate conditions of a free-standing slabs. Our findings establish a practical route toward fully integrated all-vdW polarization optical elements, providing a foundation for nanoscale photonic architectures entirely based on layered materials.