Experimental Study On Long-distance Fidelity Transmission Of Laser Chaos Over Multi-span Optical Fiber Cascading

Chaotic secure communication(including carrier communication and key distribution)receives much attention due to its advantages of high speed,long distance,and compatibility with present communication networks.It has also promoted the rapid development of chaotic secure communication technology.Due to the current demand for optical fiber communication networks,chaotic security communication is mainly faced with two major problems: how to improve the transmission rate and distance.For the rate problem,researchers have made many useful explorations.So many efforts have been devoted to improving the carrier communication and key distribution rates to the order of Gb/s.In recent years,how to improve the transmission distance of chaotic signals has also received extensive attention from researchers.In the existing chaotic secure communication system,dispersion compensation fiber(DCF)and erbium-doped fiber amplifier(EDFA)are mainly used to compensate the dispersion and loss of fiber link.Chaotic synchronization of the order of 100 kilometers of metropolitan area network has been realized experimentally.The amplified spontaneous emission(ASE)of optical amplifier,fiber dispersion and nonlinearity are the main factors that limit the distance of chaotic synchronization.In this thesis,by further reducing the damage of the above factors to the chaotic signal,the distance of fidelity transmission of chaotic signal is increased to the order of thousands of kilometers.The details are as follows:(1)The system of long-distance transmission of laser chaos over single-span fiber is experimentally constructed.And influences of the filtering width,dispersion compensation deviation and fiber input power on chaotic signal fidelity are studied.Taking synchronization0.9 as the standard,it is confirmed that the limit distance of single-span fiber chaotic synchronization is 200 km,and the corresponding chaotic signal fidelity is 0.92.Under the condition that the fiber output power is equal to the fiber input power,the influence of fiber input power on chaotic signal fidelity is studied.And taking a fidelity of 0.99 as the standard,the length of the single-span fiber link is optimized.Then,the chaotic laser transmission with distance of 720 km and fidelity of 0.922 is realized by EDFA relaying.(2)The system of long-distance transmission of laser chaos by hybrid amplification relaying is experimentally constructed.Taking the advantage of low equivalent noise figure of distributed fiber Raman amplifier(DFRA),combined with EDFA,a high-gain,low-noise hybrid amplifier can be obtained,which can effectively reduce the influence of ASE noise.Under the condition that the fiber output power is equal to the fiber input power,influences of fiber input power and gain ratio on chaotic signal fidelity was experimentally studied.And the optimal single-span fiber link length is 130 km,which is measured by the fiber loop experimental setup.Finally,under the condition of single-span fiber length of 130 km and 8-span cascade,chaotic laser transmission with distance of 1040 km and fidelity of 0.947 is realized by using the direct transmission link.Driven by above chaotic signal,the co-drive chaotic synchronization with distance of 1040 km and synchronization of 0.915 is achieved,the bandwidth of the synchronous chaotic signal is 9.6 GHz.In this research,asymmetric co-drive chaotic synchronization over a thousand kilometers is realized,which can be used in chaotic carrier communication and key distribution systems for intercity network communication.