Study On Preparation And Regulation Of Optical Source In Quantum Key Distribution System

Quantum secure communication is a cryptosystem based on the theory of quantum mechanics,and an unconditionally secure cryptosystem is realized through a "one-time-one-secret" encryption method.Since an ideal single photon source is difficult to prepare,a weak coherent optical source is used in an actual quantum key distribution(QKD)system.The QKD system requires quantum optical sources with the characteristics of wavelength consistency and stability,high power stability,and high modulation rate.Therefore,how to obtain a stable,efficient,and reliable single photon source is one of the important research directions in quantum information.This dissertation first introduces the theoretical basis and classical protocols of the QKD,analyzes the working principle and characteristics of semiconductor lasers,and explains the principle of gain switching for generating ultra-narrow optical pulses.Because the QKD system has extremely high requirements on the stability of the optical source,especially the consistency and stability of the wavelength of light emitted by the laser and the stability of the light intensity,it directly affects the coding rate and the security of the system.In this dissertation,based on the polarization coded BB84 protocol,a QKD system optical source preparation and control scheme is designed,including:trigger control of synchronous light and signal-state light,optical path synchronization scheme,and support decoy-state scheme.Specifically,the optical path design analysis,optical source driver circuit design,and related FPGA logic development are performed.For the distributed feedback(DFB)laser operating characteristics,the design of the laser voltage bias circuit,narrow pulse drive circuit,and an effective temperature control unit.Through experimental tests,the DFB laser temperature control can be stabilized within 0.02 °C.The laser driver circuit modulates the quality of the optical pulse to meet the requirements of the QKD system.The wavelength drift of the light pulse can be controlled within 0.01 nm.The standard deviation of jitter of the pulse of the signal light pulse relative to the rising edge of the synchronous light is 6.59 ps.The method for preparing and regulating the optical source can meet the requirements of the QKD system on the optical source,and makes the QKD system more stable.