Moiré-type Pancharatnam–Berry phase element enabled tunable polarization-rotating Bessel beam

Pancharatnam–Berry (PB) phase elements are widely used for optical field modulation due to their precise control over beam amplitude and phase. However, conventional PB elements are inherently static, with fixed modulation functions post-fabrication, limiting their adaptability in complex application scenarios. In this paper, we propose a moiré-type PB element comprising two specially designed PB elements. The proposed element attaches the two spin states with rotation-dependent PB phases while preserving the spin, thereby enabling dynamic rotation-tunability of the PB phase. As a functional validation, we experimentally demonstrate the dynamic control over the rotation rate of the polarization-rotating beam. The moiré-type PB element was designed using the checkerboard-phase encoding method and fabricated in liquid crystal via SD1-based micro-lithography. A back-propagation correction is introduced to eliminate the diffraction effects caused by the element gap. An adjustable rotation rate of ±240 deg /cm is achieved through ±160 deg angular offset. Owing to its compact structure with high integration and operation simplicity, the moiré-type PB element offers a novel dynamic modulation solution for structured light field generation, particle manipulation, and advanced laser processing.