Angularly Tunable Unidirectional Emission via Excitation‐Site‐Driven Momentum Engineering

Precise control of light emission directionality is crucial for quantum communication, bioimaging, optical sensing, and optical display. Luminescent materials such as quantum dots (QDs) typically exhibit omnidirectional, spontaneous, and incoherent emission, posing challenges for controllability of incoherent light. Although several strategies have been developed to achieve directional fluorescence emission, creating the angle‐tunable freedom for unidirectional emission control remains unsolved. Here, we propose an extensible momentum‐engineered strategy and experimentally demonstrate a light‐emitting metasurface that enables unidirectional emission tunability of fluorescence via excitation‐site‐driven method. By choosing different excitation sites, the guided‐mode fluorescence emitted from quantum dots undergoes customized momentum engineering along the on‐chip oblique‐lattice metasurface, thereby enabling efficient unidirectional emission into free space with controllable angular direction. This momentum‐engineering strategy provides a versatile and scalable platform for multifunctional emission manipulation, promising diverse potential applications in nanophotonics and light‐emitting devices.