Spin-Dependent Optical Geometric Transformation for Cylindrical Vector Beam Multiplexing Communication

Given by the Shannon theorem, the data rate in a single mode fiber is approaching the capacity limit of 100 Tbit/s, which even applies to all existing wavelength division multiplexing and advanced modulation formatting techniques. Optical vortex beams, including orbital angular momentum (OAM) beams with phase singularities and cylindrical vector beams (CVBs) with polarization singularities, are orthogonally structured light beams providing new degrees of freedom for multiplexing optical communication, for which the multiplexer is the key component. Although there are various OAM detection approaches such as the optical geometric transformation and vortex grating, CVB sorting with high efficiency and large dynamic range has not been demonstrated before. In this work, we propose and demonstrate an efficient approach for multiple coaxial CVB sorting based on the spin-dependent optical geometric transformation using the Pancharatnam-Berry optical element device fabricated with the photoaligned liquid crystal. We demonstrate a CVB multiplexing communication system in both free space and few-mode optical fiber. The CVB sorter is compatible with wavelength division multiplexing and shows the potential to further increase the communication capacity by 1-2 orders of magnitude.