单跨光纤长距离混沌激光保真传输实验研究

Experiment on Long-Distance Fidelity Transmission of Laser Chaos over Single-Span Optical Fiber

混沌激光在载波通信、密钥分发等信息安全传输领域具有巨大的应用潜力,但放大器自发辐射噪声、光纤色散以及非线性效应会降低混沌信号的保真度,进而限制单跨光纤混沌同步的距离。本文通过研究滤波器线宽、光纤色散补偿偏差以及混沌入纤功率对混沌激光传输保真度的影响,探明了单跨光纤混沌同步的极限距离,并在实验中实现了200 km单跨光纤中保真度为0.9214的混沌信号传输。以此信号为驱动,获得了同步系数为0.9043的共驱混沌同步,为长距离混沌载波通信与密钥分发的实现提供了基础。

Objective Chaotic secure communication,including carrier communication and key distribution,has been widely studied owing to its advantages of high speed,long distance,and compatibility with current communication networks.For practical applications in communication networks,the rate and distance of chaotic secure communication are factors that must be considered.Much effort has been devoted to improving the rate to the order of gigabits per second.In terms of distance,it has been extensively reported that chaotic transmission over a singlespan fiber of approximately 100 km can be realized experimentally.However,the transmission limit of singlespan fibers remains unclear.It is worth noting that,the fidelity of laser chaos is degraded by the amplified spontaneous emission noise of optical amplifiers,as well as fiber dispersion and nonlinearity,thus affecting the transmission distance.In this study,by optimizing the filtering width,dispersion compensation deviation,and input fiber power,the aforementioned influences on the transmission performance are reduced,and the distance limit of chaotic transmission over a singlespan fiber is ascertained.In the experiment,chaotic transmission over a 200 km singlespan fiber with a fidelity of 0.9214 is achieved.Driven by this chaotic signal,commonly driven chaos synchronization with a synchronization coefficient of 0.9043 is obtained.This provides a basis for longdistance chaotic carrier communication and key distribution.Methods We used a semiconductor subject to external optical feedback to generate laser chaos as the drive signal.To meet the nput power of the fiber,an erbiumdoped fiber amplifier(EDFA)was used to preamplify the drive signal.Then,the drive signal was divided into two branches:one branch was directly transmitted to the local response laser,and the other was transmitted to the remote response laser through the singlespan and dispersioncompensated fibers.In the transmission path,an EDFA and optical filter were arranged to compensate for the power loss of the fiber and reduce the amplified spontaneous emission(ASE)noise of the EDFA,respectively.In the experiment,the effects of the filtering width,dispersion compensation deviation,and fiber input power on the transmission fidelity of laser chaos over single fibers with different lengths were investigated in detail,and the optimized parameters to realize the transmission limit were ascertained.Finally,to realize chaos synchronization,the drive signals before and after transmission were injected separately into the response lasers with matched parameters.Results and Discussions Filtering width,fiber dispersion compensation deviation,and fiber input power are important factors that affect the fidelity of chaotic transmission.After amplification by the EDFA,ASE noise is involved in the chaotic signal,degrading the fidelity of the chaotic transmission.An optical filter suppresses the ASE noise.The most appropriate filtering width(0.2 nm)was confirmed(Fig.4).Furthermore,an optimized dispersion compensation deviation of 0 ps/nm was achieved in the scenario with a fiber length of 90 km while the filtering width was set to 0.2 nm(Fig.5).In addition to the ASE noise and fiber dispersion,fiber nonlinearity can also affect transmission fidelity:the greater the fiber input power,the greater the nonlinearityinduced distortion.With the optimized filtering width and dispersion compensation deviation,the most appropriate fiber input power of 3.1 mW was identified for a fiber length of 90 km(Fig.6).For a larger fiber length,the optimized power increased correspondingly.Finally,chaotic transmission over singlespan fibers with different lengths was examined,and a transmission limit of 200 km with a fidelity of 0.9214 was achieved experimentally,with a filtering width of 0.2 nm,dispersion compensation deviation of 0 ps/nm,and fiber input power of 18 mW(Fig.7).Driven by the laser chaos after 200 km transmission,longdistance chaos synchronization with a synchronization coefficient of 0.9043 was obtained(Fig.8).Conclusions In this study,the effects of the filtering width,fiber dispersion compensation deviation,and fiber input power on the fidelity of chaotic transmission were investigated experimentally.The transmission limit over a singlespan fiber is confirmed.With filtering width of 0.2 nm,a dispersion compensation deviation of 0 ps/nm,fiber input power of 18 mW,and 200 km chaotic transmission distance with a fidelity of 0.9214 are realized.By using the laser chaos after 200 km transmission as the drive,longdistance chaos synchronization with a synchronization coefficient of 0.9043 is obtained,providing a basis for chaotic carrier communication and key distribution oriented toward metro area networks.