Research on energy transfer characteristics for liquid crystal polarization gratings under conical incidence

This study reports the energy transfer characteristics between diffraction orders of the liquid crystal polarization grating (LCPG) under conical incidence, aiming to provide a valuable reference for developing a high-performance cascaded LCPG system. Firstly, the expression of the diffraction efficiency under conical incidence is derived, and thus, the distribution characteristics of the diffraction efficiency can be investigated by numerical calculation. Meanwhile, the resonance deviation is also introduced based on the Bragg condition to elucidate the transfer mechanism of the lightwave energy between diffraction orders. The results show that the diffraction efficiency of the +1 order decreases progressively as the conical incidence deviates from the Bragg condition, and the attenuated energy is mainly transferred into the zero order. Furthermore, the difference in diffraction efficiency between different pointing azimuths amplifies with increasing incident polar angle, which is significantly exacerbated by reducing the grating period. This indicates that the incident azimuth angle possesses a non-negligible influence on the distribution of diffraction efficiency in a 2D cascaded LCPG system with a wide angular domain. Finally, the azimuth-dependent effects on the diffraction efficiency under conical incidence are experimentally confirmed and consistent with theoretical predictions.