Metacavities by harnessing the linear-crossing metamaterials.

The formed optical cavity mode intensively relies on the size and geometry of optical cavity. When the defect or impurity exists inside the cavity, the formed cavity mode will be destroyed. Here, we propose a metacavity consisting of arrays of linear-crossing metamaterials (LCMMs) with abnormal dispersion, where each LCMM offers both the directional propagation channel for all incident angles and the negative refraction across its neighboring LCMMs. Such metacavity can be efficiently excited by a point source, where the excited wave vector components propagate along the same optical path in the cavity. More importantly, the proposed metacavity possesses the remarkable feature of partial defect immunity and geometry robustness. Assisted by two-dimensional transmission lines with loaded-circuit elements, a metacavity with partial defect immunity has been experimentally realized. Our work offers a new avenue for designing optical resonators excited by the point source in integrated photonics, which is very useful for high-efficiency filters, ultrasensitive sensors, and enhancement of light-matter interactions.