  Taking advantages of ultra-narrow bandwidth and high noise rejection
performance of the Faraday anomalous dispersion optical filter (FADOF),
simultaneously with the coherent amplification of atomic stimulated emission, a
stimulated amplified Faraday anomalous dispersion optical filter (SAFADOF) at
cesium 1470 nm is realized. The SAFADOF is able to significantly amplify very
weak laser signals and reject noise in order to obtain clean signals in strong
background. Experiment results show that, for a weak signal of 50 pW, the gain
factor can be larger than 25000 (44 dB) within a bandwidth as narrow as 13 MHz.
Having this ability to amplify weak signals with low background contribution,
the SAFADOF finds outstanding potential applications in weak signal detections.
