Multifunctional manipulation of optical fields with multiple degrees of freedom is essential for integrated photonic systems, yet achieving coordinated and independent control of polarization and phase remains challenging. Here, we propose a polarization-tunable multifocal metalens enabled by a bilayer metasurface with integrated polarization rotation. By introducing the interlayer rotation angle difference as an additional degree of freedom, a rigorous theoretical framework is established, revealing that the transmitted polarization undergoes a deterministic rotation equal to twice the interlayer rotation difference while preserving its ellipticity. Under circularly polarized incidence, the polarization state remains unchanged, with only geometric phase modulation induced. This mechanism enables a continuous and predictable mapping between input and output polarization states. By further incorporating an independent propagation phase via selected nanopillars, polarization and phase can be engineered independently within a unified framework. Based on this strategy, a polarization-tunable multifocal metalens is numerically demonstrated, generating multiple focal spots with distinct and switchable polarization states at predefined positions. The polarization state at each focus can be tuned solely by varying the incident polarization angle, without modifying the device structure. This work provides a versatile and physically intuitive strategy for multifunctional metasurface design and integrated photonic applications.
Wang et al. (Sun,) studied this question.