Research On All-optical Regeneration In Free-space Optical Communication Networks

With the rapid development of space technology and the continuous innovation of space science and technology,the capacity of spatial data increases rapidly.Microwave communication is limited by its transmission bandwidth,so it is difficult to meet the requirements of massive spatial high-speed data transmission in the order of dozens or even hundreds of Gbps.Free-space optical communication has become the research hotspot and development trend of space technology in recent years because of its remarkable advantages such as high speed,wide bandwidth,strong anti-jamming ability,good confidentiality and so on.In the free-space optical communication system,the signal is affected by atmospheric absorption,scattering,turbulence and the divergence angle of laser,which leads to the deterioration of signal quality after long-distance spatial transmission.The data transmission needs of subsequent nodes cannot be satisfied,so all-optical signal regeneration processing needs to be carried out at network nodes.Based on the requirement of high-speed data multi-hop transmission in free-space optical communication network,aiming at the deterioration of signal quality after long-distance transmission of laser link in space,combines the link budget for geosynchronous(GEO)to optical ground station(OGS),an all-optical phase regeneration technique for high-speed laser signals based on phase-sensitive four-wave mixing parameter effect is studied.The reliability of the scheme is effectively verified by exploring the principle,simulation analysis and experimental construction of the technical scheme.The main research contents include:1.The system composition,main characteristics and remarkable advantages of free-space optical communication compared with optical fiber communication and microwave communication are introduced.The present situation of free-space optical communication at home and abroad is described and the future development trend is summarized.In view of the influence of atmosphere on the free-space optical communication link,the necessity of all-optical regeneration is briefly explained.Finally,the research status of all-optical regeneration technology is described in detail.2.The theoretical principles of four-wave mixing and phase matching are described in detail.The gain and phase characteristics of interferometric and non-interferometric phase-sensitive amplifier are analyzed numerically by using Matlab software,and the basic model of non-interferometric phase-sensitive amplifier is established.Analyzing the decode-and-forward and amplify-and-forward systems which are widely used in free-space optical communication systems.The phase regeneration scheme in optical fiber can be combined with the all-optical amplify-and-forward scheme in space laser communication,aiming at the deterioration of signal quality due to the atmospheric channel and the divergence angle of laser beam in the free-space optical communication link.The all-optical signal regeneration of laser link is realized by using the principle of phase-sensitive and four-wave mixing.3.An all-optical signal regeneration scheme of cascade four-wave mixing is designed based on the free-space optical communication link budget of geosynchronous(GEO)to optical ground station(OGS).Based on OptiSystem software,the all-optical regeneration scheme with 10 Gbps communication rate and OOK and DPSK modulation format is simulated and built.The simulation results are in good agreement with the numerical results.The signal-to-noise ratio of the output signal of the OOK all-optical regeneration scheme is about 3.3 dB higher than that of the unregenerated deterioration signal,and the average optimization of the BER of the system is about three orders of magnitude.Signal-to-noise of output signal of DPSK all-optical phase regeneration scheme is improved about 3 dB,and the average optimization of the BER of the system is about four orders of magnitude.It is shown that the all-optical regeneration system can not only improve the output signal power of OOK and DPSK,but also restrain the noise accumulated in the process of spatial transmission,effectively realize the all-optical regeneration of OOK and DPSK optical signals,and improve the overall performance of the free-space optical communication system.4.An experimental scheme of all-optical signal regeneration in free-space optical communication based on the principle of four-wave mixing and phasesensitive amplifier is proposed.The regeneration characteristics of optical signal with 5Gbps communication rate and OOK and DPSK modulation format are studied.The experimental results show that the two schemes of EDFA and FWM can regenerate the degraded signal and improve the optical signal-to-noise ratio and eye diagram quality of the degraded signal for the OOK signal all-optical regeneration experiment.For DPSK signal phase regeneration experiment,with the change of relative phase,the signal gain will be periodically changed to 2?.The PS Swing can reach to 10 dB.When the output power is-39 dBm,the phase-regenerated signal eye diagram is obviously better than the non-regenerated signal eye diagram,indicating that the all-optical phase regeneration system can enhance the power of DPSK optical signal and restrain the phase noise accumulated in the process of free-space optical communication.The experiment verifies the feasibility of all-optical regeneration scheme.