In this Letter, we investigate steady states of fiber lasers mode-locked with a nonlinear amplifying loop mirror that have an inherent amplitude-noise-suppression mechanism. Due to the interaction of the sinusoidal transmission function with the fluctuating intracavity pulse amplitude, we show that under specific preconditions, this mechanism may lead to a detectable difference in relative intensity noise at the reflected and transmitted output port of the laser. We present systematic intensity noise measurements with a nonlinear fiber-based system that replicates a single roundtrip in the laser cavity. The experimental results and simulations clearly show a reduction of the intracavity amplitude fluctuations up to 4 dB for certain steady states.

In this Letter, we investigate a Yb-doped mode-locked fiber oscillator that uses coherent pulse division and recombination to avoid excessive nonlinear phase shifts. The mode locking mechanism of the laser is based on the accumulation of a differential nonlinear phase between orthogonal polarization modes in the polarization-maintaining fiber segment. The inserted coherent pulse divider, based on YVO4 crystals rotated successively by 45°, enables stable and undistorted mode-locked steady states. The output pulse energy is increased from 89 pJ in the nondivided operation by ≈6.5 dB to more than 400 pJ with three divisions. A measurement of amplitude fluctuations reveals a simultaneous broadband noise suppression of up to ≈9 dB in the frequency range from 10 kHz to 2 MHz.

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 polarizationmaintaining fiber amplifier in combination with an implemented sinusoidal transmission-function. The resulting correlation between the input intensityfluctuations 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.