Wavelength-Division Holographic Multiplexing via Cascaded Metasurfaces and THz-Spaced Microresonator Frequency Combs.

Achieving high-density wavelength multiplexing is essential for expanding the capacity of optical information processing. However, traditional optical components lack sufficient dispersion control, hindering high-efficiency, low-crosstalk wavefront manipulation across densely spaced channels. Here, we overcome this bottleneck by introducing a double-layer cascaded metasurface architecture engineered via an end-to-end differentiable design framework. Through joint optimization, this cascaded design yields a 25-fold increase in multiplexing density over single-layer approaches, theoretically enabling 64-channel holographic multiplexing with a tight 4.3-nm spacing in the visible spectrum. Furthermore, we experimentally validate this architecture in the infrared band by utilizing a terahertz-spaced microresonator frequency comb as a multi-wavelength coherent source. This first-of-its-kind integration of differentiable cascaded metasurfaces with on-chip microresonator frequency combs provides a compact, highly efficient pathway for next-generation wavelength-division multiplexing, high-capacity data communications, and integrated photonic systems.