Photonic correlation of multi-GHz signals - Application to aperture synthesis in radio astronomy

Standard digital correlators, which rely on signal acquisition and processing, are intrinsically limited by the clock jitter of analog-to-digital converters, and by the real-time processing capabilities of digital electronics. Here we demonstrate a new analog correlator architecture based on a simple photonic platform, suitable for processing broadband RF signals. The system provides real-time access to the entire correlation function of two signals by simultaneously calculating the cross-correlation coefficients for 200 values of their relative delay. The time step can be adjusted from a few ns to a few ps, enabling us to process signals with bandwidths ranging from MHz to multi-GHz. We have applied this architecture to a testbench experiment of astronomical interferometry on the sun, at 10 GHz.