Cylindrical vector beam sorting based on anisotropic geometric optical transformation

Abstract

Optical vortex beams, including the orbital angular momentum beam (OAM) with the phase singularity and cylindrical vector beams (CVBs) with the polarization singularity, are orthogonal structured light beams providing a new degree of freedom for multiplexing optical communications. There are already several mature approaches for the OAM detection such as the fork grating and geometric optical transformation. However, the technique for efficient CVBs sorting has not been demonstrated yet. In this work, we propose and demonstrate the efficient sorting of multiple CVBs based on the anisotropic geometric optical transformation approach using the Pancharatnam-Berry optical element (PBOE) device. The device is fabricated by the photo-alignment liquid crystal (LC) in a thin film with a total pixel number of 768×768 and a pixel size of 11.7μm. Since the PBOE has the circular polarizations selective property, the device can independently modulate the left-handed circular polarized and right-handed circular polarized light components of CVB. The anisotropic geometric optical transformation is capable of transforming the CVB from the donut shape to two straight lines shape. Through the phase correction and a Fourier transform by lens focusing, the CVBs is finally converted to a single light spot with a lateral displacement proportional to the input CVBs orders. In the proof of concept experiment, we demonstrated the CVBs sorting from -10 to 10 orders with an efficiency up to 61.7%. We also demonstrated multiple coaxial CVBs demultiplexing. The CVB sorting approach shows potential applications in optical multiplexing communication.