Construction of Bound States in the Continuum in Evanescent Field for On‐Chip Diffraction Engineering

ABSTRACT Recent advancements in silicon photonics have enabled the integration of diverse optical devices. However, efficiently bridging guided modes with free‐space radiation remains challenging, as current grating solutions often necessitate intricate 3D structures to enable subtle and independent control of radiation channels in multiple directions. Bound States in the Continuum (BIC) offer a promising solution due to their ability to remain localized within the radiation continuum. In this work, we propose and experimentally demonstrate, for the first time, a method that harnesses quasi‐BIC (qBIC) in the evanescent field to build a toolset for guided‐radiation interface, enabling controlled switching of radiation channels. To validate the method's capabilities, we implement it in a grating structure and showcase its potential through a 128‐channel optical phased array (OPA), which achieves enhanced diffraction control and improved far‐field beam quality. The proposed method significantly improves upon traditional grating technologies, offering a promising approach for advanced photonic integration.