Waveguides formed by etching, proton-exchange (PE), and strip-loaded on single-crystal\nlithium niobate (LN) thin film were designed and simulated by a full-vectorial finite difference method.\nThe single-mode condition, optical power distribution, and bending loss of these kinds of waveguides\nwere studied and compared systematically. For the PE waveguide, the optical power distributed in\nLN layer had negligible change with the increase of PE thickness. For the strip-loaded waveguide,\nthe relationships between optical power distribution in LN layer and waveguide thickness were\ndifferent for quasi-TE (q-TE) and quasi-TM (q-TM) modes. The bending loss would decrease with\nthe increase of bending radius. There was a bending loss caused by the electromagnetic field leakage\nwhen the neff of q-TM waveguide was smaller than that of nearby TE planar waveguide. LN ridge\nwaveguides possessed a low bending loss even at a relatively small bending radius. This study is\nhelpful for the understanding of waveguide structures as well as for the optimization and the fabrication\nof high-density integrated optical components.
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