Research Into Design And Fabrication Tehnology Of MgO-doped Lithium Niobate Optical Ridge Waveguide

The all-optical signal processing using lithium niobate waveguides has distinctadvantages of ultra-fast response and low noise, which has been widely applied in recentyears. Fabrication of high quality lithium niobate waveguides has always been achallenging topic over the past decades, but this technology is still insane in china.Searching for excellent performances and easy processing fabrication methods for lithiumniobate waveguide devices is meaningful for all-optical signal processing.In this dissertation, structures of different kinds of MgO doped lithium niobate ridgewaveguides, such as direct-bonded ridge waveguides, adhesive-bonded ridge waveguidesand annealed-proton exchange ridge waveguide, are modeled and designed. Thencorresponding fabrication processes are investigated. Through the combination of annealedproton-exchange and precise diamond blade dicing, a nonlinear wavelength conversion issuccessfully realized based on the annealed proton-annealed periodically poled MgO-dopedlithium niobate ridge waveguide. The detailed research contents can be found as follows.(1) The analytical solutions to second-harmonic generation is derived under thenon-depletion approximation. The waveguide parameters that influence the convertedoutput power, such as waveguide length, the effective interaction area, quasi-phase matchconditions, nonlinear coefficient are discussed. And the ways to enhance converted outputpower are obtained. We get that the ordinary light corresponds to transverse electric modeand extraordinary light corresponds to transverse magnetic mode in lithium niobatewaveguide. The MgO-doped lithium niobate is chosen as the substrate of lithium niobatewaveguide because of its high resistance to photorefractive. The design rules of lithiumniobate waveguide are obtained from material choice and waveguide sizes.(2) The modeling of the waveguides device with Finite-Difference Method (FDM)calculating eigen field distribution and Finite-Difference Beam Propagation Method(FD-BPM) calculating propagated field distribution are established based on MatlabProgramme. The optimized waveguide size, fundamental mode field distributions offundamental light1550nm and second-harmonic light775nm, the effective mode effectiveindex and the propagated mode field distributions of direct-bonded MgO-doped lithium niobate ridge waveguide and annealed-proton exchanged MgO-doped lithium niobate ridgewaveguide are obtained.(3) A new BCB-bonded MgO-doped LiNbO3-on-insulator (LNOI) rib waveguidestructure that can allow single-mode propagation at both fundamental wavelength andsecond-harmonic wavelength is designed. The calculated results indicate that hightsecond-harmonic generation efficiency can be potentially achieved based on this newlydesigned waveguide due to the waveguide layer and adhesive layer high index contrast andsmall waveguide sizes.(4) The fabrication processes of direct-bonded MgO-doped lithium niobate ridgewaveguide which through the combination of direct-bonded technology and InductivelyCoupled Plasma (ICP) dry etching technology, are investigated experimentally. Thefabrication parameters and optimization of the fabrication process are presented in detail. Aridge-shaped direct-bonded MgO-doped lithium niobate waveguide and adhesive-bondedMgO-doped lithium niobate waveguide are fabricated successfully.(5) The fabrication processes of annealed-proton exchange periodically poledMgO-doped lithium niobate ridge waveguide which through the combination ofannealed-proton exchange technology and precise diamond blade dicing technology, areresearched experimentally. Wavelength converter based on annealed-proton exchangeperiodically poled MgO-doped lithium niobate ridge waveguide is realized.(6) The characteristics of the fabricated annealed-proton exchange periodically poledMgO-doped lithium niobate ridge waveguide are measured. With truncation method, thepropagation loss is obtained. Then the waveguide is packaged by UV dispensing method.All optical broadcast wavelength conversion based on cascaded second-harmonic generationand difference-frequency generation and cascaded sum-and difference-frequency generationare achieved in the fabricated ridge waveguide.