my substrate is LiNbo3 and waveguide is fabricated by ti diffusion method. i dont know how to simulate the diffusion of titanium. in fact i cant find a certain refractive index to simulate the diffusion
It is important to know in which wavelength you are working on. If you are working on a telecommunications optical modulator, you must get the refractive index in the telecommunications range. As far as I know, LiNbo3 has no imaginary part and it varies greatly in different wavelength ranges. If you work in the wavelength range of 400 nm to 1200 nm, use the following link.
Article Refractive Indices of Lithium Niobate as a Function of Tempe...