Passive, Noiseless, Intensity Amplification of Repetitive Signals
  Amplification of signal intensity is essential for initiating physical processes, diagnostics, sensing, communications, and scientific measurement. During traditional amplification, the signal is amplified by multiplying the signal carriers through an active gain process using an external power source. However, for repetitive waveforms, sufficient energy for amplification often resides in the signal itself. In such cases, the unneeded external power is wasted, and the signal is additionally degraded by noise and distortions that accompany active gain processes. We show noiseless, intensity amplification of repetitive optical pulse waveforms with a gain from 2 to ~20 without using active gain, by recycling energy already stored in the input repetitive signal. This "green" method uses dispersion-induced self-imaging (Talbot) effects to precisely re-distribute the original signal energy into fewer replica waveforms. This approach simply requires a suitable manipulation of the input signal's phase profile along the temporal and spectral domains. In addition, we show experimentally how our passive amplifier performs a real-time average of the wave train to reduce noise fluctuation present on the input pulse train, as well as enhances the extinction ratio of pulses to stand above the noise floor by approximately the passive gain factor. Finally, our technique is applicable to repetitive waveforms in any spectral region or wave system, including acoustic, mechanical, and quantum probability waveforms, for which active amplification methods are challenging to implement or nonexistent. 
R. Maram, J. van Howe, M. Li and J. Aza\~na
physics.optics