Atomic processing of optically carried RF signals

Rare earth ions embedded in crystals are natural high-quality-factor resonators that can be used for processing optically-carried broadband radio-frequency signals. This chapter focuses on the radio-frequency spectrum analysis function and describes different architectures that are designed to reach tens of gigahertz instantaneous bandwidth with sub-megahertz resolution. Various approaches are considered. The active material may act as a spectral buffer memory. Instead one may store a processing function inside the crystal. The latter may then operate either as a frequency-to-angle converter or a frequency-to-time transformer. All those architectures have been explored experimentally. To meet the specific requirements of these processors, frequency agile lasers have been developed. These keynote devices are described in detail.