Dependence of Optical Losses on the Thickness of the Buffer Layer Between a Thin-film Lithium Niobate Waveguide and a Metal Electrode

The optical losses in the intersection region of a gold electrode and a thin-film lithium niobate optical waveguide are investigated. It is possible to reduce the absorption of optical radiation in the waveguide by selecting the buffer layer thickness. Using the finite element method and the Mueller and Newton–Raphson numerical methods, the dependence of the optical losses in the waveguide on the buffer layer thickness is determined. It is shown that when the buffer layer thickness changes from zero to one micrometer, the optical losses in the intersection region of the waveguide and the electrode decrease from 6·102 to 10–3 dB/cm for the fundamental TM mode and from 102 to 10–3 dB/cm for the fundamental TE mode. The correctness of the calculation is confirmed by the consistency of the data obtained by three different methods. The results can be used in designing functional elements of photonic integrated circuits (phase, amplitude modulators, etc.) with minimal optical losses due to absorption of gold electrodes.