Why Raman amplification ?

Raman amplification of optically carried RF signals is shown to be a good alternative to erbium-doped-fiber amplification. In the case of continuous RF signal, RIN levels as low as -160 dB/Hz, limited by the laser source, are obtained. Moreover, when the RF signal is no more continuous, such as real radar waveforms, we evidence that Raman amplification overcomes erbium-doped-fiber amplification. Improvement of the pulse-to-pulse RF phase stability of 17 dB is observed. This result is attributed to the nature of Raman amplification, which does not involve transient variations of the population inversion across the whole spectral range covered by radar waveforms.