| Quantum integrated optics has developed rapidly in recent years and has become an important development direction of quantum optics and quantum information technology.Compared with bulk quantum optics,integrated quantum optics has the characteristics of small size,high stability,strong manipulation,and reconfiguration.As one of the most important nonlinear optical materials,lithium niobate is widely used in the preparation of quantum resources and the high-speed control of quantum states.With the introduction of micromachining technology,lithium niobate has become important platforms for integrated quantum optics,realizing a monolithic integrated entangled resource with multiple-degrees-of-freedom encoding.However,the wavelength tuning range of the on-chip entangled resource is limited,which cannot adapt to the working wavelength of external optical devices and the requirements of different application scenarios.Moreover,due to the error of micromachining technology,the quality of the on-chip tunable quantum resources based on lithium niobate waveguide needs to be improved.In recent years,lithium niobate film has rapidly developed into a new material system,and most of the research on it is the field of classical nonlinear optics.Its application in quantum optics still needs in-depth exploration and research.On the one hand,this thesis is dedicated to the traditional proton-exchange lithium niobate waveguide chip,and hasdeveloped a wavelength-tunable high-quality path and frequency entangled resources;on the other hand,it studies the dispersion characteristics of lithium niobate thin film waveguide and proposes a new scheme of preparation of polarization entangled resources.The main research results obtained in this paper are as follows:1.Theoretical analysis of the transmission characteristics of Mach-Zehnder(MZI)interferometer composed of unbalanced beam splitters.Through the analysis of the general form of MZI transfer matrix,we get the theoretical conditions and scope of application that MZI can be equivalent to an accurate 50:50 beam splitter.We also analyze and calculate the quantum interference of two-photon NOON states with degenerate and non-degenerate wavelength in MZI,and obtain the conditions for high-quality path entanglement and frequency entanglement.2.Prepare high-quality wavelength-tunable path entangled photon pairs and frequency entangled photon pairs.In the proton-exchange lithium niobate waveguide chip,the Mach–Zehnder(MZI)interferometer is used as beam splitter with a precisely controllable splitting ratio to achieve high-visibility two-photon interference.At the same time,a cascaded multi-period poling structure is used to extend the wavelength of the photon pair,and prepare wavelength-tunable path entangled photon pairs.Since the splitting ratio of the MZI controlled by the electro-optical effect can accurately reach the ideal splitting ratio at different wavelengths,and the compensation voltage in the MZI is symmetrical about the center wavelength,we also prepare wavelength-tunable frequency entangled photon pairs based the same chip.The Hong-Ou-Mandel(HOM)interference is used to characterize the prepared identical photon pairs and frequency entangled photon pairs.3.Propose a scheme of single-period backward propagation polarization entanglement resource.The lithium niobate film on the insulator(LNOI)can be processed into a strongly bound waveguide,and the dispersion of the strongly bound waveguide can be adjusted by designing the waveguide cross section.We designed the intersecting TM00 and TE00 refractive index dispersion curves in a single straight waveguide.This type of dispersion curve can naturally realize the quasi-phase matching of two different backward parameter down-conversion processes at the same time,and can directly prepare a polarization entanglement source.We also analyzed the experimental feasibility,that is,the influence of micromachining processing on such polarization entanglement sources. |
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