Single-layer quadratic phase transmissive metasurface enabling wavelength-controlled lateral–focus scanning

We propose a single-layer quadratic phase transmissive metasurface (MS) that enables continuous wavelength-controlled lateral focus scanning under oblique incidence. By employing a laterally translated quadratic phase profile, the focal spot of obliquely incident light is positioned on the optical axis of the MS at the designed center incident wavelength. As the incident wavelength varies, the focal position shifts laterally on the focal plane. This operation provides precise and rapid lateral focus control without mechanical motion or active tuning elements. Additionally, the design incorporates a large depth of focus (DOF), ensuring stable focusing performance and maintaining a nearly constant focal spot size across the entire operating wavelength range. The fabricated device was experimentally characterized across the C- and L-bands from 1530 to 1600 nm, achieving a lateral scan range of 321 µm and a stable focusing efficiency of approximately 55%. This compact, vibration-free MS provides a high-speed, broadband platform for focal control.