Research On All-optical Repeater Based On Nonlinear-optical Loop Mirror

With the rapid development of ultra-high speed optical networks,the high-spectralefficiency modulation format,the effective communication distance of optical network transmission system,and the nonlinear Shannon limit have become the research hotspot.The amplified spontaneous emission(ASE)noise accumulated in the transmission process,and the nonlinear damages caused by optical fibers are the key factors limiting the capacity of optical network system.The traditional optical-electrical-optical repeater technology brings the problems including complex signal multiplexing/demultiplexing process,and so-called “electronic bottleneck”,causing that it is unable to meet the requirements of signal repeaters in the future ultra-large capacity,long-distance transmission optical network.Therefore,it is necessary to develop new repeater technology to further promote the development of high-speed all-optical network.The all-optical repeater based on the nonlinear effect of optical devices can directly suppress the signal distortion in the optical domain.Besides,this technology owns the T-bit signal processing speed which meets the signal processing requirements of high-speed alloptical networks.This thesis breaks through the limitation that the traditional all-optical repeater can only deal with the amplitude noise for on-off keying(OOK)signals,and focuses on all-optical regeneration for high-order modulation format to implement the repeater function in coherent communication systems.The main contents and innovations of this thesis are as follows:1.All-optical regeneration of multiple phase-shift keying(M-PSK)signals was carried out based on attenuator nonlinear-optical loop mirror(Att-NOLM)structure.The Att-NOLM theoretical analysis model was constructed to optimize parameters such as the attenuator coefficient and the coupling coefficient in the interferometer.Moreover,it was applied to explore the optimization of power-transferring function(PTF)and phasetransferring function(Ph TF),enabling achieving the phase preserving amplitude regeneration for M-PSK signals.Through the thoughtful optimization,the signal quality was improved up to 2.6d B and the phase residual was only 0.15 d B after the repeater.2.A novel conjugated nonlinear-optical loop mirror(Conj-NOLM)structure is proposed to achieve all-optical regeneration for high-order quadrature amplitude modulation(QAM)formats.The Conj-NOLM regenerator was constructed by connecting two NOLMs with a conjugate converter.The parameters of coupling coefficient and power compensation were optimized jointly to achieve the phase preserving amplitude regeneration function.In the optimized Conj-NOLM structure,the signal quality of the16-QAM is improved by 1.8d B,and the phase residual is controlled at the level of 1.38 d B.3.The experimental test on the optimization of the Att-NOLM regenerator is carried out.The effects of both the length of the highly nonlinear fiber and the coupling coefficient of the optical coupler in Att-NOLM structure were tested in the view of the PTF mapping curve.The impact of the attenuator coefficient on the regeneration interval and the working point position was analyzed.The noise suppression performance of an Att-NOLM repeater was analyzed through simulation and experiment.