Slab mode position in grating or slot ring resonator.


I am performing 2.5D simulation of slot ring resonator and grating ring resonator. I am kind of struck regarding the position of slab mode. In the normal ring resonator example as long as the slab mode position is in silicon layer the response remains same. But for the structure like slot ring or grating ring where should i put the slab mode (slot or slab in the slot ring sturcture or high index or low index region in the grating ring resonator ). OR is there another way to perform the 2.5 FDTD simulaton of those type of structures?

i would really appreciate any help/suggestion.
thank you.

Eigenmode 위치 선정 질문

Hi @ktwayana

I don’t have a clear answer for your question at the moment and we might end up using 3D FDTD simulations to get more precise results. Can you please share your simulation files? Then we can take a look and see what settings are optimal/make sense.


thanks for your response. Actually, i did the 3D FDTD simulation but i need to simulate it for a couple of time (varying index and gap between ring and bus). The simulation file is grating_ring1.fsp (2.6 MB)
and its response is . could you please suggest me the optimal setting for this structure.


Dear @ktwayana

Thank you very much for sharing the file. It was very helpful to understand the geometry and have some intuition of what we expect to see.

varFDTD works very well for cases where the material thickness (waveguide and ring) and their refractive index along the material remains constant. For your case, we can build the geometry in Mode->varFDTD and choose the slab mode position on the non-etched area as the spacing between the grating seems to be 4 times smaller than the gratings.

Can you please prepare the simulation file on Mode Solutions and report me the results? A sweep over refractive index might be required later on, but this should be a good starting point.

I will wait for your response :slight_smile:


Dear @bkhanaliloo,
thank you very much.
The Mode->varFDTD simulation file of my structure is ring_grating.lms (1.9 MB)
x . The Tx and Rx response is and when slab mode is at non etched position and etched position respectively (these responses are completely different than what i got from 3D FDTD metbod).
could you please guide me about ‘sweep over refractive index’ so that i can get response similar to 3D-FDTD method.
Thank you.

Slot waveguide and its equivalent strip waveguide

Dear @ktwayana

Its an unfortunate that we can’t solve it using varFDTD and clearly it is because we don’t have symmetry along the z-axis of the device (which means the structure can’t be considered as planar structure).

Originally I was thinking if the FSR in varFDTD is smaller than 3D simulations, we can run a sweep over refractive index. But I guess that idea won’t work here.

It looks like we can get exact results only via FDTD. If I find a solution later on, I will let you know.



Dear @bkhanaliloo

Thank you very much. I greatly appreciate your valuable time and effort.