Single mode and multimode ridgewaveguide laser




I am simulating a ridgewaveguide laser layer structure to analyse its TE modes. In my simulation I am facing some of these problems

  1. I have calculted modes and the mode with largest effective index (3.366492) is ‘1’ which is fundamental TE mode? But when I select fundamental mode then I get a mode with second largest neff, that is 3.36643. Can I please know the my fundamental mode TE is not the one with highest neff?

  2. Mode should be confined under the ridge in ‘active’ layer but what I see from ‘YZ profile monitor’ is a mode that is not confined under the RWG, but its at the position of pink arrow of mode source. How can I know is this mode confined in a right layer?

  3. If I select fundamenal TE mode source, I get ‘-0.281168’ T_backward (from mode expansion monitor), but if I launch more modes then T_backward in fundamental mode changes. Isn’t T_backward in fundamental mode should remain same if I launch other modes?

  4. Finally, is there any way I can confirm that my RWG is fundamental TE mode?

  5. Is there any way I can confirm that my ridgewaveguide is a fundamental TE mode.


Here is my simulation GaAs_RWG.lms (702.2 KB)


Hi @nouman.zia

  1. The first mode is TM mode. When the TE polarization factor is zero, it means that the mode is TM polarized.

2,3,4,5. The green cross in your simulation is placed outside the varFDTD region. Please place it on top of waveguide to make sure that simulation is set properly and check the injected mode from the effective index tab. Blue crosses can be outside the varFDTD region, but green cross should be located on top of waveguide.

4,5: If the fundamental mode is injected I expect it will be propagated over the waveguide. You can use profile monitors to check and make sure that proper mode is propagated. I believe the confusion is caused because the green cross was located outside varFDTD and you were injecting proper mode.

Please rerun the modified simulations and keep me updated if you had further questions.

Please limit your post to one question so that we can address it properly before moving on the next question.


Thank you @bkhanaliloo!
Problem still exists in injecting the right mode. I have attached a modiifed simulation with green cross on the top of RWGGaAs_RWG.lms (512.1 KB)


Hi @nouman.zia

The plot shows the effective index as a function of z in the waveguide:

As you can see, the p_active object has the highest material index. Is this intended? I was expecting the ridge waveguide to have the highest effective index.

As a result there are many different supported modes. Here are some of the interesting modes:

The mode has to be properly selected. Once you confirm the mode, we can study its propagation in the waveguide.