How to do a VarFDTD simulation in frequency domain

mode
fdtd

#1

Hi, Lumerical team,

I am doing an optical nonlinear effect simulation, I only found examples in time domain, power changes with time. Is there any way to do the simulation in frequency domain with different input powers? So that I can simulate the spectrums or effective index of a waveguide in different input power cases.

I would appreciate any help from you!

Best regards,
W.Wang


#2

Hi @wwang73

Here is the link to nonlinear material:
https://kb.lumerical.com/en/index.html?materials_advanced_material_models.html

What type of nonlinear material are you interested in? The simulation results can be returned in frequency domain. Please elaborate more on the application that you want to simulate.


#3

Hello, bkhanaliloo,

I am simulating a LiNbO3 rib waveguide with varFDTD, and the file is attached. I already used the Chi2/Chi3 material model in the simulation, the effective index results did not change when I changed the source amplitude. How can I get the effective index of this waveguide when the optical power is different?

Attached is the simulation file:
LN_Nonlinear wg.lms (357.9 KB)

Regards,
W.Wang


#4

Hi @wwang73

How did you check the effective index of the mode? Please note that index monitors will return the material index and effective mode index assuming source amplitude is 1. The perturbation in the index of nonlinear material can be calculated as is explained in the link below:
https://www.rp-photonics.com/nonlinear_index.html

You can still study the perturbation in the material index by, for example, calculating Fresnel equations at different powers:
https://en.wikipedia.org/wiki/Fresnel_equations

I hope this was helpful.


#5

Hello, bkhanaliloo,

I know I can calculate the refractive index perturbation of a material. However, since the E-field of the mode inside the waveguide is different at different position, I cannot use the index perturbation in the simulation. How can I simulate the effective index change?

Regards,
W.Wang


#6

Hi @wwang73

This is not very trivial.

I can think of one possible solution: you can obtain the field intensity at every time domain step and then update the material index for the next step using the nk import:
https://kb.lumerical.com/en/index.html?ref_sim_obj_importing_spatial_nk.html
https://kb.lumerical.com/en/index.html?device_ref_sim_obj_import_nk_material.html

A similar approach is used in the link below:
https://kb.lumerical.com/en/index.html?nanophotonic_applications_polymer_curing.html

Then with the updated material index, you can run FDE to calculate effective index results. You can also do these simulations in FDTD. nk-import object should allow you to capture the change in material index as function of intensity and position.

I hope this was helpful.