Increasing the design degree of freedom for polarization through multilayer synchronous polarization projection

The degrees of freedom (DoFs) of light determine the maximum number of independent signal channels an optical system can support. However, the polarization DoF is intrinsically limited to two by orthogonality, which causes unavoidable crosstalk and often forces position multiplexing, where different channels are assigned to distinct spatial locations to suppress crosstalk. This research introduces a multilayer synchronous polarization projection method that fundamentally increases the DoF for polarization multiplexing. The DoF equals twice the number of projection layers. We experimentally demonstrate six- channel polarization multiplexing holography without position multiplexing. The six-channel multiplexing results indicate that our approach exceeds the conventional polarization multiplexing method, yielding an average 3.79 dB improvement in extinction ratio across the six channels. Compared with the theoretical limit of traditional polarization multiplexing, our method reduces crosstalk by an average of 6.52 dB across all channels in a seven-channel design. The polarization projection method breaks the DoF limitation of polarization multiplexing, opening a path toward high-dimensional photonic information encoding for communication, encryption, and imaging.