Abstract
Periodically-Poled LiNbO3 waveguide (PPLN WG) is an attractive integrated nonlinear device for high-efficient nonlinear frequency conversion applications. There are numerous competitive techniques to form the optical waveguide in LiNbO3, such as liquid-phase proton exchange (LPE), annealing liquid-phase proton exchange (APE), reverse proton exchange (RPE), soft proton exchange (SPE), and high-temperature proton exchange (HTPE). This work introduced the vapor phase proton exchange (VPE) process and applied it to fabricate the high-quality waveguide devices. The features of the planar waveguide by the VPE process have been accurately characterized using the prism coupler, x-ray diffractometer, and spectrophotometer. Also, the diffusions under various parameters such as temperature (260℃~325℃), process durations (3h~72h), and hydrogen concentration with lithium benzoate are analyzed.It is believed that the diffusion rate balanced between the direct proton exchange and annealing leads to the index change and particular phase structure in the VPE process. A pure crystalline phase κ2 can be obtained directly via the VPE process. Theκ2 phase suffers smaller strains and lower refractive index change than the β mixture phases from the LPE. The post-exchange annealing will cause a phase transition from theκ2 phase toward the α phase with a graded index-like profile which is confirmed to have a low loss feature, and to include the recovered nonlinear coefficient. The α phase obtained using the annealing VPE (AVPE) procedure is even clearer and purer than that obtained using the APE procedure (from the comparison of the x-ray rocking curve peaks). That result indicates the possibility to fabricate even lower loss and high efficient waveguide devices.The program for simulating the AVPE diffusion behavior is also established in this thesis. Index profile can be fully constructed within the wavelength range of the revised Sellmeier equation. Additionally, the first optical result of the PPLN WG fabricated by the AVPE method is demonstrated and characterized. Although the device suffers low conversion efficiency for various reasons, these problems can be overcome using the available techniques. Undoubtedly, considerable room remains for improvements and optimizations of the proposed procedure.