Multifunctional Metasurface for Simultaneous Light Manipulation under Both Guided-Wave and Free-Space Incidence

Metasurfaces have outstanding capabilities in manipulating light, enabling functions such as focusing, vortex beam generation, and holography. Such versatile light manipulation, initially studied in free-space optics, has recently been explored in integrated photonics, with light control in waveguides. The ability to achieve multifunctional multiplexing stands is a significant advantage of metasurfaces, and investigating metasurfaces capable of simultaneously accommodating free-space light and guided waves holds the potential to enhance the information capacity and offer extensive application possibilities. However, research in this particular domain is limited, and achieving independent control of these two incident modes without introducing wavelength-dependent degrees of freedom remains a challenging frontier. To solve this problem, we combine the detour phase and resonant phase altogether into on-chip metasurfaces for the first time, which provides extra phase degrees of freedom for independent control of both on-ship and free-space channels. We propose and experimentally demonstrate this novel design with an on-chip multifunctional metasurface that enables the independent control of free-space light and guided waves without the need for introducing additional wavelength-related variables. By controlling the polarization of free-space light and incident direction of guided light, the designed device can achieve a record-high six-channel multifunctional multiplexing hologram and image display.