Please refer to this example: https://optics.ansys.com/hc/en-us/articles/360042338014-Thermally-tuned-waveguide-FEEM-
once you import the temperature data (attribute) with given voltage, you can sweep the voltage or voltage point. Then you can get neff as a function of voltage. However it is not with temperature, as the temperature is a spatial distribution and it is not a single value at each voltage.
Please check the example and see if you can duplicate the result, and then modify it to fit your need.
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