Cladding‐Free On‐Chip Ultracompact Photonic Devices

Cladding layers are seemingly indispensable components in photonic integrated circuits to confine light and prevent cross‐talk, which, however, fundamentally limit miniaturization and integration capabilities. Zero‐spacing waveguide arrays enabled by photonic crystals with shifted spatial dispersions provide a potential solution to the above challenge, whose demonstration, however, has been limited to microwaves. Here, on‐chip ultracompact cladding‐free waveguide arrays with 100% space utilization efficiency at terahertz frequencies are reported on an all‐silicon platform. Different from the previous approach operating along one single dimension, the design can work in two dimensions, allowing for a concept of cladding‐free resonators that are previously unattainable. The experimental results show a high inter‐channel separation between two neighbor zero‐spacing waveguides and a communication data rate of 12.8 Gbit s−1 per channel. The work provides a promising on‐chip cladding‐free solution for high‐density optical/THz integrated circuits and opens a route toward broadband datalinks, offering transformative potential for information processing and 6G‐to‐XG communications.