Mode index does not change on changing the doping concentration



I am currently working with lumerical device.After I run the charge simulator and export the charge data using the charge monitor , I run FEEM solver while making an nk import for the charge distribution and check out the mode an its effective index.The problem is that the effective index of the mode does not change even if I change the doping concentration or If I import an optical generation source which is completely not logical.Note that I do this without applying a voltage because I would like to find the effect of change of the effective index when changing the doping concentration only.


Hi @hoda-essam

Can you please provide simulation files for a review?

Also, can you try to run the simulations for different charge distribution and then visualize the effective index results?



lumerical.ldev (9.7 MB)
Kindly find attached the simulation file.If I remove the doping or the solar generation I get the same effective index for the mode.


Hi @hoda-essam

It looks like the applied voltage in your nk-import is set to zero. This maybe one reason why you are not seeing change in the effective index. The other thing is that change in effective index is in the order 1e-4–1e-5 and you need to lock the mesh to make sure that your results are not affected by mesh mismatch between different applied voltages. Please visit the link below for MZI application example:


Hi ,
Thank for your reply. But I am actually setting the voltage =0 on purpose to find the change in effective index due to doping and solar generation not due to applied voltage .So how can I do that ?


Hi @hoda-essam

The imported nk object should have the perturbed index data while in your case it seems to be just the charge data. Please use the script file provided in the MZI application example to create the perturbed index data (see the Index Perturbation of this direct: Other than this make sure that mesh is refined and you are using the lock mesh option.

Hope this solves the problem.


Hi @bkhanaliloo ,

Thank you for your reply I now understand where the problem is .I just have a problem that I am working with wavelength 5 Microns where as the silicon model used by the script in The mach_zender example only has data for wavelengths 1.3 and 1.55 Microns. I tried to write an equivalent script for the drude expansion model and I would be grateful if you have a look and let me know if it is correct that way or not.Also I would like to know does the NP Density Grid Attribute in mode and FDTD solvers work for Silicon model only or can I use it to calculate the perturbed index at 5 Microns.
Kindly find attached the script.


index_perterbation.lsf (2.3 KB)