A model incorporating noise and pump depletion in a Brillouin amplifier (BA) predicts a fundamental limitation on attainable pump-to-signal-ratio extraction efficiency. Experimental data supporting this model are also presented. In spite of the limitation, an experimental technique is shown that results in a factor-of-7 increase in extraction efficiency. We accomplish this by noise suppressing and subsequently double passing a BA. We report an overall power efficiency of 37% and phase-conjugate amplification of 3.75 × 1010 for a signal input power near the noise level. This performance, which is the best to our knowledge recorded to date, is accomplished without requiring additional input energy.
© 1995 Optical Society of America
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