Silicon‐Waveguide‐Integrated High‐Quality Metagrating Supporting Bound State in the Continuum

Abstract The photonic bound state in the continuum (BIC) is a spatially bounded eigen state that can be realized in the form of a supercavity mode with an ultrahigh quality factor. The high‐quality supercavity resonance can be supported by photonic crystal slabs, asymmetric metasurfaces, and high‐contrast gratings. However, these schemes all suffer from bulky device size and complex experimental setup. Herein, a silicon‐waveguide‐integrated high‐quality metagrating is proposed and demonstrated as a new platform to manipulate the supercavity mode. The shallow‐ridge metagrating is directly embedded in the silicon slab waveguide, so the input slab mode can be coupled into the resonant ridge mode, which can be further transformed into the supercavity mode by utilizing the intra‐waveguide Fabry–Perot interference. Such an effect has been experimentally verified by the fabricated devices. The metagrating operating near the supercavity regime is also experimentally realized with a high quality factor ≈5200. As an application, such high‐quality metagrating is exploited to realize the temperature sensing with a high temperature sensitivity ≈77 pm K −1 . The proposed integrated metagrating provides a novel approach to harness the BIC, paving ways for a new class of BIC‐based nanophotonic devices with high performance, chip‐scale footprint, and long‐term stability.