Expérimental
Time reversal is a technique based on the invariance of the wave propagation equation in an inhomogeneous medium. It ensures spatial and temporal refocusing of a wave after having recorded the transmission channel signature. When the propagation medium is non-stationary, the transmission channel characteristics keep changing. The time-reversed signal must be sent as quickly as possible, otherwise the refocusing will not be effective. In the first demonstrations of time-reversal with RF waves, analog-to-digital converters (ADC) were used, limiting the processing bandwidth. In the aim of reaching the GHz regime, the latency time becomes problematic because of the limited sampling rate of ADCs. Conversely, a fully analog solution has the advantage of avoiding this conversion step. At Institut Langevin, we design original analog architectures for processing optically-carried radiofrequency signals based on light-matter interaction in rare-earth ion-doped crystals. In particular we recently proposed an architecture able to generate controlled, time-reversed copies of arbitrary waveforms. The goal of the internship will be to advance the development of this time-reversal processor, first using arbitrary signals and then using real RF signals reverberated in a cavity.