Ultrathin high-performance circular polarizers based on MoOCl2/NbOCl2 van der Waals heterostructures

Circularly polarized light (CPL) holds immense promise for diverse applications, including 3D displays, quantum information processing, biosensing, and optical imaging. However, high-performance, ultrathin, and easily integrable devices for CPL manipulation and discrimination remain a significant challenge. Leveraging the phase modulation capability of the natural 2D van der Waals material NbOCl2 and the polarization selectivity of MoOCl2, we propose and demonstrate a lithography-free, easy-to-fabricate, ultrathin circular polarizer. The MoOCl2/NbOCl2 stacked nanoplates with submicrometer total thicknesses demonstrate pronounced discrimination between left- and right-handed CPL at designed visible wavelengths, achieving a maximum extinction ratio of 21.16 dB at 653 nm for a stack with a total thickness of approximately 730 nm. Furthermore, an approximately 690-nm-thick stacked device was integrated with an LED chip operating at a center wavelength of 580 nm, with an estimated degree of circular polarization (DOCP) reaching 99.68%, demonstrating the compatibility of the proposed circular polarizer with compact light-emitting platforms. This work provides a versatile strategy for constructing ultrathin, integrable circularly polarized photonic devices by leveraging the intrinsic optical anisotropy of natural low-dimensional materials, and demonstrates broad application prospects in chiral light-field detectors and on-chip circularly polarized light sources. Circularly polarized light can be used in several applications, but normally requires bulky optical components. Here, the authors report the realization of sub-micron-thick circular polarizers based on the natural phase modulation capability of NbOCl2 and polarization selectivity of MoOCl2 crystals, showing their integration into a LED chip.