Vertical Coupling

mode

#1

Hi,

I would like to couple light vertically to a grating, using a waveguide. I am taking the example from the phas shifted bragg grating.

https://kb.lumerical.com/en/pic_passive_bragg_phase_shifted.html

My question is can I modify the ports in the above example to as I shown in the attached figure. I want to input light from the waveguide above the grating. Is it correct physics?
Because I read about coupling of evanscent waves in the following example and it followed a very complex treatment.

https://kb.lumerical.com/en/pic_passive_waveguide_couplers_evanescent.html
Please let me know.


#2

Sorry forgot to upload my simulation set-up


#3

It should be possible to simulate this structure, but one thing to be careful of in the setup is to make sure you have selected the correct port modes.

I noticed that the waveguide extends through the x min and x max boundaries of the solver region, but the structures don’t have to extend through the boundaries in order for them to be included in the port mode calculations. Since the structure you are coupling to below the waveguide extends the ports, the cross section of the structure which is used to find the port modes will include both the waveguide as well as the structure below. If you instead wanted to simulate a structure where the waveguide is longer than the structure that is being coupled to so that the port injects the waveguide mode and not a coupled mode of the waveguide and structure below, then you should include one extra cell where only the input waveguide is present and the coupling structure is not present.

Please let me know if my explanation is unclear.