Improvement of DPSK transmission by phase-preserving amplitude regeneration using cascaded nonlinear amplifying loop mirrors

Experimental results obtained on 10 Gb/s RZ-DPSK transmission in a recirculating fiber-loop setup have shown that nonlinear amplifying loop mirrors (NALM) can efficiently enhance system performance: cascaded phase-preserving amplitude regeneration can efficiently prevent the accumulation of amplitude and nonlinear phase noise components in such systems. It was possible to significantly augment the transmitted signal quality; alternatively a considerable increase of fiber launch power could be achieved. Amplified Rayleigh backscattering in the highly nonlinear fiber in the NALM has been identified as main limiting effect when the regenerator is passed multiple times.