Research On Basic Devices Of Lithium Niobate Integrated Photonics

Since the theory of integrated optics was put forward,the research of integrated photonic devices which based on optical waveguide structure has developed rapidly.Lithium niobate has excellent acousto-optic,electro-optic,nonlinear optical properties,and a high transmittance in the visible and infrared bands,which is known as "optical silicon".With the development of fabrication technology,integrated photon devices based on lithium niobate have been widely studied,including high-speed electro-optic modulators,frequency combs,nonlinear frequency conversion devices and so on,demonstrating the application prospects of lithium niobate integrated photonics.In this paper,theoretical analysis and numerical simulation of several lithium niobate integrated photonics devices are proposed based on the research status of lithium niobate integrated photonics.The main research contents of this paper include:1.In the introduction,we briefly review the development of integrated optics,introduce the material characteristics of lithium niobate and application prospect,research significance and related research progress of integrated photonic device based on lithium niobate.2.In this part,we elaborate the basic theory of optical waveguide,including the simple classification,electromagnetic field theory with different flat dimensions.Then we introduce several lithium niobate waveguides and fabrication processes,establishing a basis for the research work of lithium niobate integrated photon devices.3.Analyzing and numerical simulating two kinds of lithium niobate waveguide couplers.One is a broadband directional coupler based on an asymmetric waveguide.Based on the coupling mode theory and the transmission matrix,we get the basic range of optimal scale.The entire structures are further simulated and optimized using the three-dimensional finite-difference time-domain method.After that,we simulate a lowloss mode size converter for coupling between a standard lensed fiber and lithium niobate waveguides.The coupler consists of two inverse tapers that improve the mode matching area and improve the coupling efficiency.We optimize the specific parameters of the coupler.4.In Chapter 4,we introduce the research status of vortex beam source.Based on the nonlinear Cherenkov phase matching,we propose a new integrated scheme to generate frequency-doubled vortex beams.Its principle is that the near-infrared fundamental wave is resonant in the radially poled lithium niobate micro-ring resonator,while the second harmonic is emitted from the resonator along the Cherenkov phasematching direction.It is found that the topological charge of the emitted second harmonic vortex beam is determined by both the azimuthal order of the whispering galley modes and the number of nonlinear grating elements.In addition,the optical field distribution and conversion efficiency of SHG are studied systematically.