Identification of the Optimal Value of the Dithering Tone Frequency to Mitigate Rayleigh-Backscattering-Induced Distortion in Radioastronomic Scenarios

In the context of the Radio over Fiber downlinks belonging to the Aperture Array Verification System (AAVS) of the low frequency Square Kilometre Array (SKA-LOW) radio telescope, the combination of modulation of the optical carrier by Radio Frequency Interfering Tones (RFIs) and fiber-induced Rayleigh Backscattering (RBS) determines the presence of undesired spurious frequency terms. A successful countermeasure to the phenomenon has been proposed, based on the additional modulation with a low frequency tone (called dithering tone) which mitigates such distortions exploiting the laser chirp effect. In the present work, through a rigorous theoretical and experimental study, the optimal design parameters of such solution are put into evidence, showing that an appropriate choice of the dithering tone frequency allows to reduce to acceptable levels the RBS induced nonlinearities, while minimizing the power consumption of the corresponding introduced devices.