MMI coupler_S parameter


#1

Hi,
I am trying to improve the example model with 2 output ports to calculate S parameter for single port.
But the S parameters look so weird, S21 is 0.51. S31 is 0.77. The transmission power from 2 ports is higher than input.


The original model is from
https://kb.lumerical.com/en/pic_passive_waveguide_couplers_mmi.html
MMI_simple.lms (413.2 KB)

Could you please help me to modify my model?
Thank you very much!
Qi


#2

Another issue is that the through powers are different. It doesn’t make sense.
Thanks,
Qi


#3

Hi @qi.han.1

S parameters show the ratio of electric fields:
https://kb.lumerical.com/en/index.html?metamaterials_s_parameters.html

If you want to obtain transmission, you need to set the scalar operation to, say, abs(S21)^2.

Regarding your second inquiry, this is because the mode profile on the output waveguides are not the same:


Please make sure that you are choosing the proper mode in each waveguide.


#5

Hi, bkhanaliloo
I figure it out, the default port activated the “use full simulation span” , I need to unclick it.
Thank you very much for your help!
Qi