Numerical demonstration of LWIR multi-focus metalenses with polarization conversion

Long-wave infrared (LWIR) imaging technology offers several advantages, including strong adaptability, a long range, and resistance to color interference, making it an important means of target detection. To promote the lightweight and multi-function integration of the LWIR imaging system and expand its application scenarios, two Pancharatnam-Berry (PB) phase multi-focus metalenses are designed, with a focusing efficiency of at least 50%. The PB phase modulation mechanism is closely related to the polarization state of the incident light. To solve the problems of quarter-wave plates being thick and difficult to integrate, as well as reducing system efficiency, a metasurface was proposed that can convert linearly polarized light to circularly polarized light in a broadband (10-11.5 μm) and integrate it into the back of the multi-focus metalenses. Multi-focus metalenses with polarization conversion functions offer the advantages of high integration and rapid reactivity, providing what we believe to be a new approach to designing complex functional optical systems.