On-chip nonlocal metasurface for color router: conquering efficiency-loss from spatial-multiplexing

Metasurfaces integrated onto guided-wave photonic systems have been investigated for enabling advanced functionalities such as point-by-point optical extraction and manipulation of amplitude, phase, and polarization. However, achieving full control over the spectrum (i.e., wavelength/frequency) of on-chip light remains a challenge, limiting their widespread application in integrated photonics. Here, we propose and experimentally demonstrate an on-chip metasurface color router by leveraging symmetry-broken quasi-bound states in the continuum (q-BICs) mode. By precisely engineering the on-chip meta-diatom pairs with controlled scaling and asymmetry, we simultaneously achieve modulation of both extraction intensity and narrowband spectral extraction of the out-coupled lightwave. As a proof of concept, we realize several on-chip multiplexed color routers through spatial mapping and cascading of distinct q-BIC-assisted meta-diatom pixels, capable of selectively guiding and routing primary wavelengths into free space from different spatial positions along the waveguide. Crucially, due to the on-chip optical propagation scheme, these color routers, enabled by nonlocal metasurfaces, exhibit spatial multiplexing but with a significant improvement in the energy utilization efficiency (EUE) compared with conventional designs. We envision that such on-chip q-BIC-assisted metasurface color routers, with their potential for miniaturized integration, could open new avenues for advanced applications in multiplexed information routing, intelligent integrated photonic systems, and next-generation wearable display technologies.