Design of an orbital angular momentum demultiplexing system based on off-axis cascaded metasurfaces

When designing metasurface systems, the actual efficiency of the metasurface is much different from the theoretical design efficiency. This can lead to stray light caused by insufficient modulation efficiency of the metasurfaces, which acts as background noise and is magnified in cascaded metasurface systems step by step, affecting system functionality. To reduce the impact of metasurfaces with limited efficiency on system performance, this paper proposes a design method for an orbital angular momentum demultiplexing system based on off-axis cascaded metasurfaces. By incorporating an off-axis phase design, the stray light generated by the reduced efficiency of the metasurface in a cascaded metasurface system is effectively eliminated. Using FDTD (finite difference time domain) simulation software for calculation and validation, the results demonstrate that the off-axis cascaded metasurface system can effectively reduce stray light caused by insufficient modulation efficiency. Compared to the on-axis system, it achieves a maximum reduction in crosstalk of 4.15 dB and an average of 80% stray light elimination, showing a significant performance advantage.