Ultrahigh-speed optical encryption enabled by spatiotemporal noise chaffing.

Optical encryption provides strong physical-layer security but is limited by the slow response of spatial light modulators. We propose and experimentally demonstrate a spatiotemporal noise chaffing system inspired by the "chaffing and winnowing" principle for ultrahigh-speed temporal encryption. By exploiting the symmetric spatial properties and orthogonality of conjugated orbital angular momentum (OAM) states, high-speed temporal signals ("wheat") and spatial noise ("chaff") are simultaneously encoded. This mechanism suppresses information leakage by degrading the temporal signal-to-noise ratio while enabling authorized recovery. Furthermore, a variable-weight multimodal OAM (VW-multimodal OAM) scheme combined with a multimodal generation neural network (MGNN) exponentially expands the key space beyond 10¹⁰. Experimentally, a record secure transmission rate of 1.25 Tbps per mode is achieved in an eight-channel wavelength-division-multiplexed coherent link. The product of rate and key space surpasses existing methods by five orders of magnitude, establishing a new photonic-security paradigm for future ultrafast and secure communication networks.