Multi-delay photonic correlator for wideband RF signal processing

Correlation of RF signals is a fundamental operation in many fields such as information processing, detection and imaging techniques at large. Because of the intrinsic limitations of electronic techniques, standard digital correlators, which rely on the acquisition of signals and their processing, become very complex to implement for the real-time analysis of signals whose bandwidth exceeds a few hundred MHz. In this article, we report a novel analog correlator architecture based on multi-heterodyne interferometry implemented in a simple photonic platform, suitable for wideband RF signal processing. It gives access in real time, to the entire analog correlation function of two signals, by computing the cross-correlation coefficients at 200 delay time steps simultaneously. The delay time step can be adjusted, from a few ns, down to a few tens of ps, enabling to process signals with multi-GHz bandwidth. We have applied this architecture to the localization of RF transmitters by TDoA, and achieved a precision close to 10 ps for a 100 ms integration time. This architecture is expected to find practical applications in various domains, from radar and electronic warfare to telecommunications, imaging, and radio-astronomy.