High-resolution cylindrical vector beams sorting based on spin-dependent fan-out optical geometric transformation.

With growing data demands, the capacity of the single-mode fiber will reach its limit. Cylindrical vector beams (CVBs) as the eigenmodes of fiber have been demonstrated to increase the capacity in multiplexing optical communication. As a key component of CVB multiplexing, the sorter based on spin-dependent optical geometric transformation has the advantages of high efficiency and a large channel number. However, the demonstrated spatial resolution of the CVB sorter was not sufficient to separate the adjacent CVB orders. Therefore, there were still serious crosstalk issues for the CVB multiplexing channels. Here, we propose and demonstrate the high-resolution CVBs sorting by introducing fan-out structures in the spin-dependent optical geometric transformation. The crosstalk among the CVBs are suppressed compared with the original design. In addition, a cylindrical lens is used to modify the output beams to Gaussian shape. We experimentally demonstrate the sorting of 4 coaxial CVB channels to standard multimode fiber array. In the numerical modeling, we also design the CVB sorter for free space to integrated waveguide array demultiplexing.