Integrated coupled optoelectronic oscillator for ultra-low-noise and ultra-wideband tunable microwave generation

Ultra-low-noise microwave signals play a driving role in the development of modern scientific technologies such as radar, communication, and sensing. On-chip photonic integration provides an attractive approach for the implementation of ultra-low-noise microwave signal sources with attractive added advantages of being compact and lightweight, which are vitally important for real-world applications. Coupled optoelectronic oscillators (COEOs) with a hybrid structure of an optical loop and an optoelectronic loop are high-performance microwave photonic signal sources, which feature a unique advantage over conventional single-loop OEOs since they can achieve ultra-low phase noise with a relatively short cavity length. Here we report a wideband tunable ultra-low-noise integrated COEO (ICOEO), which is realized by integrating its key optoelectronic components (electro-optic modulator, photodetector, optical filter, etc.) on silicon-on-insulator (SOI). A wideband frequency tuning range from 2 GHz to 30 GHz is obtained, covering the entire S, C, X, Ku, and K bands. The phase noise is as low as −132 dBc/Hz@10 kHz, which is 19 dB better than that of the single-loop OEO with a similar cavity length. We also improved the long-term stability of the ICOEO by injection locking, and the Allan deviation of the produced microwave signal reaches 10 −12 @1 s. The high-performance ICOEO can find a wide range of applications including modern radar, electronic warfare, and communication systems.