The Research Of Quantum Communication Core Devices Based On PPLN Waveguides

Since quantum key distribution(QKD)was first introduced in 1984,the distance of QKD systems have been greatly improved over both free space and optical fibers.However,there are still some bottlenecks that limit its further development,such as frequency incompatibility:the well-developed silicon avalanche photodiode can not work in the low-loss spectral window of the fiber,the working wavelength of quantum memory can not match with that of fiber-based communication.Periodically poled lithium niobate(PPLN)waveguides are the preferable choice to overcome this difficulty,which can realize efficient frequency conversion.In this thesis,we explore reverse-proton-exchanged(RPE)PPLN waveguides in depth,including the corresponding theory,the design technique,the fabrication process and device characterization.Based on our prepared PPLN waveguides,we demonstrated a series of up-conversion single-photon detectors(UCSPD)and an interface for linking quantum memory with fiber channel.The relevant works are described as following:1.We show an integrated four-channel all-fiber UCSPD for the first time in laboratory.The compact module can satisfy different demands with adjustable efficiency and noise.2.We demonstrate a high-performance UCSPD for 1.064-?m band with two kinds of filtering scheme,achieving the detection efficiencies of 32.5%and 38%with noises of 45 cps and 700 cps respectively.3.We develop an integrated waveguides structure and apply it into efficient UCSPDs working at both signal and pump wavelength.Finally,we get the detection efficiencies of 28%for 1550 nm and 27%for 1950 nm respectively.4.We use integrated PPLN waveguides to realize an UCSPD at 1.3-?m band.By using etalons stack as the narrow-band filters,we finally achieve an ultra-low noise of 80 cps with a detection efficiency of 31%.5.We make use of integrated PPLN waveguides to conversion the quantum memory wavelength from near-infrared window to telecom O band for reducing the fiber transmission loss.We realize a first heralded entanglement between two cold atomic-ensemble quantum memories by interfering photons transmitted over a 50 km long optical fiber.Apart from QKD systems,it is conceivable that our various UCSPDs working at different spectral windows have extensive potential applications in single photon imaging,lidar,optical time domain reflectometry,single-photon-level spectrometer,environmental gas monitoring,deep space optical communication,medical devices and so forth.The heralded entanglement between two quantum memories over long-distance photon interference can function as an elementary quantum repeater segment,and pave the way towards building larger-scale quantum networks in the near future.