Low-loss plasmonic waveguide with high optical confinement on the thin-film lithium niobate-on-insulator (LNOI) platform

Thin-film lithium niobate-on-insulator (LNOI) is a promising platform for integrated photonics, offering a large second-order nonlinearity for electro-optic modulation and nonlinear applications. In this work, we develop a plasmonic waveguide on the thin-film LN which can maintain high optical confinement. By careful design, the propagation losses can be reduced to 109 dB/cm and 462 dB/cm at 1550 nm in simulation and experiment, respectively. The plasmonic waveguide has an effective mode area of only 0.064 μm², which is one order of magnitude smaller than typical thin-film LNOI waveguides. These results represent, to our knowledge, the lowest optical losses reported to date for plasmonic waveguides fabricated on thin-film LNOI. The high optical confinement enables efficient light-matter interactions and can improve the modulation efficiency of electro-optic modulators in ultra-compact devices implemented on the thin-film LNOI platform.