All-Optical Cross-Connection of Cylindrical Vector Beam Multiplexing Channels

The achievement of cylindrical vector beam (CVB) multiplexing has shown advantages in enlarging communication capacities and all-optical interconnections. While various mode transformation technologies have been developed to process CVB multiplexing signals, previous approaches have failed to cross-connect CVB channels, which could play a pivotal role in all-optical interconnection. Since CVBs can be decomposed into two orthogonal circularly polarized vortex beams with opposite topological charges, it is possible to cross-connect CVB channels via spin-dependent orbital angular momentum mode cross-transformation. Exploiting the spin-orbit interaction of photons in anisotropic liquid crystal q-plates, we performed conjugate helical phase modulations to these two spin components using the local polarization conversion of the birefringent effect, where the conjugate relationship of the two spin components was maintained during the transformation. Constrained by the spin-dependent phase modulation, the spatially separated target CVB mode was independently transformed with other higher-order modes via the partitioned modulation of the liquid crystal q-plate for CVB mode cross-transformation. As a proof of concept, a three-channel CVB multiplexing communication system was constructed. We show that the data signals between two CVB channels were successfully cross-connected, and 150 Gbit/s quadrature phase-shift keying signals were transmitted with a bit-error-rate approaching 1 × 10
⁻⁶
.