Fundamental Of Quantum Key Distribution Network

In all ages,secure communication is absolutely necessary for any person in the world.To keep the information secure,people developed a kind of special technology,named cryptography.Profiting from the competition between attack and defense,cryptography has improved to the balance of both side step by step. However,the appearance of quantum computer makes the traditional public cryptography nearly broken.A new technology for secure communication is needed exigently.Quantum key distribution(QKD) is what we need now.It can resist any eavesdropping even with the quantum computer,and will be broken only if physical rules are not reliable.The existence of so many advantages of this technology makes people spend lots of time and money on the research and get many exciting results, which include lots of theoretical schemes and cxperimental demonstrations basing on different encoding methods.The secure communication distance and transmission rate of point-to-point QKD systems have nearly reached 150 kilometers and megahertz respectively.Even some commercial systems have appears on the market. Nowadays people are striving for making this technology widely used in daily life, even though it is not perfect at all.According to the experience of classical communication,a QKD network must be built in future for the application.In a network,many users can enjoy the communication service with the use of a few equipments.That will save a lot of resource and make the price of this service lower. To build such a QKD network,many problems must be solved because there are many differences between this new system and traditional one.So we must make great efforts on this topic.The contents of this thesis are discussing how to build a QKD network. Following are the major parts:1.After introducing the basic theory of QKD technology and demonstrating many experimental systems,we proposed a new theoretical scheme basing on frequency encoding.This scheme has advantages of frequency encoding,just like other similar schemes,but makes up the hole of a prior frequency encoding scheme, proposed by a French research group,which may introduce errors in the final results. Such schemes,as well as schemes basing on phase encoding and polarization encoding,will be the basal units of QKD network.2.Because there should not be any amplifier and measurement activity in QKD network,we used wavelength division multiplexing(WDM) components to build a star-topology QKD network.The major point of this network is that optical signals will choose transmission path automatically without any measurement on the signals, which is quite different from classical communication network.We can achieve this aim because of artful connection between many WDM components.Compare with other schemes,this network is simple and efficient.3.We gathered all kinds of QKD network schemes,compared them with each other to show their own characters and classified these schemes by the components they used and the area they covered.Then we proposed a standard series to evaluate all QKD network schemes for the sake of guiding subsequent research.4.We gave a programming of secure communication system which based on QKD,described its framework and filled all issues into this frame by the subjects they concerned with,We also explained the relationships between all parts of the frame and we hope our work can help other researchers.