How to create LNoI waveguide?

There does not appear to be an attachment to this post. Can you try to attach the project file? (The one with extension .bpd)

Lithium niobate is an insulator. It can become a waveguide if Ti is diffused into the surface. What do you mean by lithium niobate on insulator(LNoI)?

In OptiBPM, one can define waveguides created by diffusion of specific metals into specific crystals. These features follow the technical process for each diffused waveguide technology. Examples can be found in OptiBPM_Tech_Background_and_Tutorials.pdf,Lesson 7: applying predefined diffusion processes. For example the substrate can be lithium niobate, the required process parameters are already defined in OptiBPM. One cannot have a substrate of dielectric material, since the diffusion process is not defined. I recommend following lesson 7 and modifying it to suit your application as far as possible.