Polarization-Dependent Varifocal Metalens with Achromatic Focusing in THz Region

Metalenses offer great potential for flexible manipulation of the electromagnetic field. However, metalens with tunable focal length and achromatic performance remains a challenge. This paper constructing a polarization-dependent superposition varifocal metalens with achromatic focusing performance in the THz region (270 - 330 GHz). The focal length of the metalens can be tuned linearly by changing the polarization angle of incidence, allowing for a tunable range of $3\lambda_{c}$ (where $\lambda_{c}$ is the wavelength at 300 GHz). Another key advantages of the varifocal metalens is that it can maintain a stable focal length for a given polarization incidence across a broad bandwidth of 20%. Within the operation band, the varifocal metalens exhibits high focusing efficiency and achieves diffraction-limited spot sizes, ensuring high-resolution imaging and sensing capabilities.