Thank you for sending the sample project file. Now I can clearly see the problem. These waveguides have been formed with a Mg stripe evaporated to lithium niobate. Magnesium diffusion causes the refractive index of LiNbO to become less, not greater. Therefore these stripes have refractive index less than the substrate. Therefore there is no mode. You ask for modal input. The mode solver fails to find it because it doesn’t exist. There will be an error message indicating a problem with mode solving. try using Titanium diffustion, instead of Magnesium!