Breaking the Coupling Among N² Fully-Connected Linear Polarization Channels with Polarization Diffraction Neural Network

Polarization multiplexing is one of the key technologies for multi-dimensional information transmission. When constructing an N²-dimensional linear polarization multiplexing network with N input states of distinct polar angle and corresponding N outputs (N > 2), there are inherent couplings for all channels due to polarization decomposition and superposition, exhibiting as information crosstalk among non-orthogonal polarization channels. Hereby employing a polarization diffraction neural network (PDNN) to minimize couplings in a global manner, N² fully-connected independent transmission channels are demonstrated by multiplexing N linear polar angles. Taking a chiral-assisted metasurface as a physical platform, which enriches physical freedoms by breaking symmetry in the longitudinal direction, a single-layer PDNN is verified through ultra-low crosstalk in digital holographic imaging. Then, PDNN is extended to a limited-aperture metasurface scenario, achieving 36 independent polarization channels multiplexing within an aperture of 18.7λ₀ × 18.7λ₀. These results exemplify the architecture's capability for complete polarization multiplexing, with direct applicability to optical linear computing, advanced holography, and high-security optical encryption.