Compact low-noise photonic-terahertz synthesizer

High-performance terahertz (THz) sources are increasingly important for next-generation communication, sensing and precision metrology systems. However, existing approaches often rely on complex system architectures, making it difficult to simultaneously achieve low noise and deployable implementations. Here we demonstrate a compact photonic THz source based on a packaged, self-injection-locked Kerr microcomb using a fiber Fabry–Pérot resonator. The device supports stable soliton operation at a repetition rate of ~ 20 GHz while preserving coherence at THz carrier frequencies. Using a soliton-crystal-derived carrier at 319 GHz, we realize 5 m free-space THz wireless communication with 16- and 64-QAM modulation at symbol rates up to 15 GBd, achieving bit-error rates well below the soft-decision forward-error-correction threshold under turnkey operation. Beyond single-carrier transmission, the microcomb also generates multiple mutually coherent THz carriers near 300 GHz with consistent noise performance. These results establish a compact and low-noise platform for coherent THz synthesis that supports both high-speed communication and parallel multi-channel operation, offering a scalable route toward high-capacity THz systems while reducing device bandwidth requirements and overall system complexity.