Tilt RWG reflection


I am interested to study the reflection of tilt RWG laser diode. Which lumerical module could help me in this. At the moment, i am trying FDTD.

I am on a beginner level and any suggestion will be highly appreciated.

Thanks in advance.

Hi Nouman,

I think FDTD Solutions is a right choice for studying the modal reflectivity of ridge waveguide with tilted facet. I have created a simple example for you to get started with.

To analyze how the input mode is coupled into various modes on reflection from the angled facet, you need to use a mode expansion monitor. For detailed information about how the mode expansion monitor works, have a look at the following page:

I think you need to add a mesh override over the facet region to avoid unwanted scattering from the facet as a result of coarse meshing.


Hello @skim,

I am using mode expansion monitor to calculate the modal reflection of tilt facets in ridge waveguide structure. I would like to know that what are the 5 different values in each output parameter (e.g T-backward) of mode expansion monitor?

My other question is that I would like to measure the modal reflection of only fundamental TE mode. So I selected the fundamental TE in both the mode source and mode expansion monitor. Now how can I find that the one out of five modal reflection ( that is T_backward…? ) values is for only fundamental TE mode?

Hi @nouman.zia

A detailed explanation about what the various results in the mode expansion monitor mean can be found in the following page (see ‘what do the results mean section’):


If you select only the fundamental TE mode in the mode expansion monitor, then the T_backward should give you the reflection into the fundamental TE modal field. If you have selected multiple modes in the mode expansion monitor, then you will have multiple T_backward values, each corresponding to the reflection into the selected modal field.

Hi @skim,

I have already selected the expansion of fundamental TE mode. My mode source is also fundamental TE.

But for each expanded parameter (e.g. T_forward, T_backward, etc) I have 5 values, even I have selected fundamental mode.

Can I know why I am getting 5 different values for each parameter in this case?

If you have only one mode chosen and are seeing 5 values for each of the T_forward, T_backward, etc., then the 5 values might be related to the frequency points you have specified. Please check the number of frequency points in your mode expansion monitor.

If this still does not answer your question, please share your simulation file so that we can have a better idea about what the issue is.

Hi @skim,
Thanks for reply! I still keep on getting 5 values after selecting one frequency point.

I have attached my script file that you can run and see simulation.tilt_facet_BD_script.lsf (6.9 KB)



It looks like you also need to set the number of frequency points being measured by the field monitor. This could be done from the script by setting the global monitor settings using the following script command:

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