  We propose a nonlinear fiber system for shot-noise limited, all-optical
intensity-noise reduction and signal amplification. The mechanism is based on
the accumulation of different nonlinear phase shifts between orthogonal
polarization modes in a polarization-maintaining fiber amplifier in combination
with an implemented sinusoidal transmission-function. The resulting correlation
between the input intensity-fluctuations and the system transmission enables
tunable intensity noise reduction of the input pulse train. In the experiment,
the noise spectral density of a mode-locked oscillator is suppressed by up to
~20 dB to the theoretical shot-noise limit of the measurement at -151.3 dBc/Hz
with simultaneous pulse amplification of 13.5dB.
