Actively Stabilized Multi-Loop Optoelectronic Oscillator Enabled by Multi-Core Fiber

We propose an approach for highly-stable and low-phase-noise microwave signal generation based on an actively stabilized multi-loop optoelectronic oscillator (ASML-OEO) by leveraging the distinctive spatial multiplexing capability of multi-core fiber (MCF). In the proposed ASML-OEO, a MCF is employed to create spatially parallel optical delay paths within a single cladding. This enables a compact multi-loop OEO design with intrinsically high side-mode suppression ratio (SMSR). To enhance the long-term frequency stability, an active time-delay compensation scheme is introduced by leveraging the inherent chromatic dispersion effect of the MCF. By precisely tuning the optical carrier wavelength, the environmentally induced time delay variations in the MCF can be dynamically compensated, thereby actively stabilizing the OEO loop. Notably, the compact multi-loop OEO design enabled by the MCF offers superior frequency stability compared to conventional designs. This enhancement stems from the fact that all fiber cores in the MCF experience nearly identical environmental disturbances, enabling precise and simultaneous time-delay compensation. The proposed system is experimentally validated, generating a 10.1-GHz signal with an SMSR of 69.6 dB and a phase noise of -124.5 dBc/Hz@10 kHz. Furthermore, active stabilization yields a remarkable improvement in long-term frequency stability, reducing the hourly peak-to-peak frequency drift from 40.2 kHz to 0.44 kHz and lowering the Allan deviation from 5.6 × 10^-11@1000s to 9.3 × 10^-13@1000s. With its simultaneous achievement of high SMSR, low phase noise, and superior frequency stability, the proposed ASML-OEO architecture is uniquely suited for demanding applications including high-resolution radar imaging, modern broadband wireless communications and advanced electronic warfare systems.