The Design Of Drive Circuit For The Phase Modulator Of Quantum Cryptography Communications Based On BB84 Protocol

Cryptography is one of the oldest applied sciences in the world. With the fast development of computer technology,especially the emergence of the idea of quantum computer,the security based on computational complexity is severely challenged.Quantum cryptography,which is a combination of quantum mechanics and cryptology,promises to solve the key distribution problem of the classical cryptography, has been developed fastly and attracts much attentions.The security of quantum cryptosystems is guaranteed by the fundaimntal laws of quantum mechanics,namely,the uncentainty principle and the no-cloning theorem,so we should not worry about eavesdropping when the quantum key distrbution is operated in a public channel.The protocols of quantum key distribution are BB84,B92,E91 and so on.The design of drive circuit for the phase modulator of quantum cryptography communications is based on BB84 protocol.The"Plug & Play" system has better optics long-term stability than the "Two asymmetric Mach-Zender" system because of the automatically compensation of the polarization mode dispersion and phase shift.The driver circuit of the phase modulaor which is the main contribution of this dissertation is one of the most pivotal technologies in quantum key distribution experiments,and it is the most important part in the "Plug&Play" system.We have researched and developped the driver circuit located in the sender part,implemented with hardware based on MCU & FPGA.The main contents of this paper are:1. The phase drive voltage and delay time set by the MCU, and then set the value of the parallel transmission to the FPGA, by generating 1MHz reference signal and the precision of 10ns coarse delay signals.2. In order to obtain the range of the delay of Ins～1ms, accuracy of Ins delay signal, we use AD9501 programmable delay chip,with coarse delay enable signal for the signal to obtain the total delay of the signal.3. In order to achieve the output voltage of phase, we use high-speed analog switch, use the total delay of the signal as enable signal of the analog switch, control 0V,2.25V.4.5V, 6.75V output voltage of different drive signal and realized our research objective.