Ring resonator and TM mode propagation


#1

Hi I Have an query related to the ring resonator, I am using Ring resonator example from knowledge base in that source uses the fundamental mode of 100% TE polarization fraction (Means TE Mode). If I am trying to use 0% ( means TM mode ) (Using user select mode option) its not propagating. What is the reason for that, How Can I solve that.

thanks in advance


Value of H is always very low in input source of ring resonator
Quality factor analysis
#2

Hello Nanda,

TE polarization fraction does not indicate if the mode is TE or TM. It indicates the polarization of the field in the plane transverse to the direction of propagation. In the ring resonator example 100% TE polarization fraction indicates that the transverse field is polarized in the y direction.

If the mode is TE or TM is indicated by the TE/TM fraction as shown here:

100% TM fraction indicates TM mode. If I try to propagate this TM mode the results seem reasonable:


Trial modes and TE/TM fraction
Low field intensity when using user select mode in varFDTD
#3

thanks mbenes.
I am trying to send the 100% TE fraction means opposite to the above u mentioned, For that I chooses the mode from source select option, and I am trying to propagate but its not propagating. how can I solve that problem. kindly let me.


#4

Thank you @Nanda for the clarification. You are right that this mode does not propagate and it is due to the varFDTD solver settings. Specifically, you need to change the “Polarization” settings on the “Effective index” tab where you select H mode™ or E mode(TE), which is indeed related to the “TE polarization fraction” as you suggested in your original post. For modes with 100% TE polarization fraction use E mode(TE) choice and for modes with 0% TE polarization fraction use H mode™ in the varFDTD settings. This settings is aligned with the TE/TM polarization definition as you mentioned it in your original post, so in this case disregard my previous comment about TE/TM fraction(explained below).

When you select the modes in the source settings, modes with various polarization will be displayed in the list regardless of the varFDTD settings, but you need to select the modes with correct polarization otherwise the results will not be reliable.

Since the TE/TM polarization definition can vary in different application areas, here is a mathematical definition of the “TE polarization fraction” and “TE/TM fraction” from Knowledge Base in order to avoid any confusion:

The “TE polarization fraction Ex” for propagation along the z direction is defined by the following equation:

where |Ex|^2+|Ey|^2 corresponds to |E_parallel|^2 (since we are considering the polarization of the modes, we only consider the fields parallel to the mode cross section). For propagation along the x/y direction (ie. “TE polarization fraction Ey/Ex”), this is similarly defined:
and

“TE/TM fraction” is defined by the following equations:
and
where and refers to the field component in the direction of propagation (ie. perpendicular to the mode cross section).


#5

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please help me! use the ring examples:
1.setting the VarFDTD neff mode as pic1
2.setting the source1 modes as pic2
run
get pic3.! why the T loss too much ?[quote=“Nanda, post:1, topic:1033, full:true”]
Hi I Have an query related to the ring resonator, I am using Ring resonator example from knowledge base in that source uses the fundamental mode of 100% TE polarization fraction (Means TE Mode). If I am trying to use 0% ( means TM mode ) (Using user select mode option) its not propagating. What is the reason for that, How Can I solve that.

thanks in advance
[/quote]


#6

hi LIucan the loss u showed is what kind of example or the design file you are using…
Once if I see the total file then I can check where the problem is.
anyhow my guess is in first case u taken z axis vs field and second case y axis vs field, U changed any launching condition of source?.
the second one yaxis vs field is correct because we have to place source in y direction (and also the loss is small that is 1e-7).


#7

@liucan

The varFDTD solver simulates either TE modes or TM modes of a device and it assumes that there is no coupling between TE and TM modes.

The application example was set up to run the simulation for TE modes. If you would like to inject a TM source instead, you need to first edit the varFDTD solver and select a slab mode with 0 TE polarization fraction instead of the slab mode that is currently selected which has a TE polarization fraction of 100. The effective indices of the varFDTD simulation are calculated based on the selected slab mode. Then, edit the source to re-calculate modes for the updated effective index values of the structure, and select the desired source mode with 0 TE fraction.

If the slab mode selected in the varFDTD solver is TE then it won’t inject TM modes properly, and vice versa if a TM slab mode is selected in the varFDTD solver, then it won’t inject TE modes properly.

Hopefully this helps.


#8

thanks very much!


#9

thank you very much!