Photonic band gap enhanced second-harmonic generation in a planar lithium niobate waveguide

Enhanced second harmonic generation (SHG) conversion efficiency was theoretically predicted in waveguide geometry with coupling to a one-dimensional grating photonic band gap (PBG). We report the first experimental results of band-edge enhanced Cerenkov SHG in a waveguide geometry. Cerenkov SHG is radiated into the substrate below the waveguide. The results are compared against a theoretical model that we designed to explore the critical design parameters of the system.; In our experiment, the samples were made with lithium niobate as the nonlinear material. By applying the proton exchange technique we fabricated a waveguide near the surface. The effective indices of waveguide modes were determined by using three techniques: prism-coupling, diffraction, and Cerenkov radiation. The WKB method was used to analyze the results. A comparison between the results derived from different methods was made to check the consistency of the methods. Ultraviolet laser lithography was used with photoresist to make PBG gratings on the sample. The photoresist gratings were used to scatter guided light in the waveguide, but initial etching experiments using an inductively coupled plasma (ICP) etcher on the photoresist gratings were also made. The photoresist and etched gratings were further characterized by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging.; An experimental setup was designed and constructed to investigate the Cerenkov second-harmonic generation (CSHG) in the substrate under band-edge resonance conditions in the waveguides. Guided SHG inside planar waveguides was also experimentally investigated. In this experiment, the second mode in the waveguide was tuned to a band-edge resonance to confine and enhance the guided electromagnetic field and enhance the nonlinear optical efficiency. In this dissertation, eight samples were investigated in detail and the highest conversion efficiency of CSHG with PBG was enhanced around 50 times above the CSHG signal without a PBG. A numerical model was successfully built to explain the experimental result. It's also found that the SHG inside the waveguides is not as strong as CSHG in the substrate.