Optical vortex generation based on spin-orbit coupling leveraging the large birefringence of van der Waals Materials

Optical vortex beams are of interest for a variety of photonic applications. One approach to generating optical vortices exploits spin-orbit coupling within light propagation in anisotropic media, where the polarization state of light is converted into orbital angular momentum. However, due to low birefringence of conventional anisotropic media, it is required to use bulky crystals to obtain high efficiency. In this context, van der Waals (vdW) crystals emerge as a promising candidate for this mechanism because of their large birefringence and low optical loss. In this work, we investigate optical vortex generation using 8-μm-thick-hexagonal boron nitride and 23-μm-thick-molybdenum disulfide (MoS2) crystals in a transmission configuration. Additionally, the efficiency of spin-orbit coupling is quantitatively analysed by varying the beam waist. For the MoS2 crystal, an experimental conversion efficiency reaches up to 0.46, close to the theoretical limit. These findings show the optical vortex generation based on micrometer-thick vdW crystals, providing an effective platform using simple method and without the necessity of nanofabrication.