Study On Low Noise Transmission Technology In Multicore-fiber-based Quantum Key Distribution Optical Networks

The emergence of quantum key distribution(QKD)technology provides a new solution to the information security problems brought about by the rapid development of computing power in the future.In recent years,the theoretical development of QKD has become more and more perfect,and it is gradually moving from the laboratory to practical applications.The next stage of development will focus on QKD networking technology.From the perspective of improving scalability and reducing implementation costs,integrating QKD with optical networks,that is,building QKD optical networks,has become an inevitable development trend.However,the noise generated by classical signals becomes one of the challenges of the QKD optical network.This thesis focuses on the problem of how to realize the co-propagation of quantum signals and classical signals in existing optical networks.Noise suppression technologies are closely related to network architecture,so this thesis proposes corresponding low-noise co-propagation transmission schemes from three scenarios of access network,metropolitan area network and inter-city network.The main research work and innovation are as follows:(1)This thesis proposes a power model of inter-core Raman scattering which can be seen as a basis of noise suppression schemes.Previously,the inter-core Raman scattering was only experimentally studied.However,the parameters of different multi-core fibers are different,so the experimental conclusions are not universal.This thesis proposes the idea of 'Inter-core Raman scattering=Raman scattering of inter-core crosstalk+Inter-core crosstalk of Raman scattering'.Based on this idea,the power model of inter-core Raman scattering is derived,and the inter-core Raman scattering is analyzed.On this basis,the properties of inter core Raman scattering and the impact of Raman scattering on QKD are analyzed.The simulation results show that the inter-core Raman scattering power is approximately linear with the inter-core coupling coefficient.(2)This thesis proposes a wavelength-time multiplexing low-noise QKD optical access network based on multi-core fiber.The previous QKD optical access network was based on single-core optical fiber.In this thesis,facing the high security,large capacity,and large number of users of the future access network,the QKD optical access network based on multi-core optical fiber is proposed.The superiority of quantum signal using wavelength-time multiplexing in QKD access network is discussed in this thesis.To deal with the noise problem of the QKD optical access network,a noise suppression core-wavelength allocation scheme is proposed for the proposed access network architecture.Finally,the experiment verified the feasibility of the proposed access network and the effectiveness of the proposed scheme.The highest secure key rate got in the experiment is 1.64 kbps(3)This thesis proposes a noise suppression frequency interleaving transmission scheme in QKD metropolitan area network.In this scheme,the classical signals and the quantum signals are frequency-interleaved.Compared with the existing scheme,the biggest advantage of this scheme is high spectrum utilization.Then with the experimental measurement,it is found that the backward inter-core crosstalk noise is less than the forward inter core crosstalk noise,that is,counter-propagation is better than the co-propagation.Finally,the experiment of coexistence is completed.The experiment verifies that the co-propagation can be realized by using frequency interleaving scheme.The maximum secure key rate of QKD is 10.8 kbps in the experiment,and the secure key rate is almost not lower than that of QKD transmission alone.(4)This thesis proposes the unified Raman scattering model in the inter-city QKD optical network.The most significant feature of the inter-city QKD optical network is the long transmission distance.At this time,the classical signals need to be amplified several times with optical amplifiers,and the use of the amplifiers greatly increase the noise power.In view of this,this thesis proposes the one-way unified Raman scattering model for the BB84 protocol,and the two-way unified Raman scattering model for the measurement-device-independent and phase-matching QKD protocols.The unified Raman scattering model can be applicable to both single-core fibers and multi-core fibres and is used to measure the Raman scattering noise power with amplifiers.Based on this model,the performance simulation of QKD in inter-city optical network shows that the co-propagation transmission distance of phase-matching QKD and classical signals can reach 300 km,which indicates that co-propagation in the inter-city QKD optical network is feasible.