Phase-preserving amplitude noise suppression using an attenuation-imbalanced NOLM

A nonlinear optical loop mirror with a bidirectional attenuator has been used for regeneration of return-to-zero differential phase-shift-keyed (RZ-DPSK) signals. A 2.5 ps, 10 Gb/s signal with amplitude fluctuations of 28 % was regenerated with a negative power penalty of 2 dB practically back to the quality of the undistorted reference signal. Parameters limiting system performance and optimization possibilities will be discussed.