CST - How to Simulate Lithium Niobate?

I am trying to design a simple Mach Zander sensor which relies on the first order linear Electro optical effect (Pockels Effect). To do this I need to define a new material Lithium Niobate: however this is proving significantly difficult! 
The materials refractive index varies with the applied E field (see attached). How would I add this material and simulate this?

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