reflectivity of VCSEL with semiconductor DBR

- November 21, 2023 at 5:42 pm
  
  Xinyu Liu
  Subscriber
  
  no idea why the reflectivity of VCSEL is always higher than 1, as shown in the following picture. Is it a parameter problem or a software problem?
- November 23, 2023 at 8:37 am
  
  Niki Papachristou
  Ansys Employee
  
  Hi Xinyu,
  Thank you for reaching out to us! Can you please provide more information on your simulation? A common reason to have ripples and tansmission higher than 1 is the fact that your simulation might not have been completed properly. This can be observed with the auto shut off level: Questions Regarding Autoshutoff level
  I hope that was helpful, let me know if I can be of further assistance.
  
  Please note that this is the optics forum and not the photonics where lumerical related question are posted. For you next lumerical question please post at: Ansys photonics forum
  
  Kind Regards,
  Niki
- November 24, 2023 at 2:08 pm
  
  Xinyu Liu
  Subscriber
  
  Hi,
  The parameter is set as follows. Is there any information you need?
- November 24, 2023 at 2:22 pm
  
  Niki Papachristou
  Ansys Employee
  
  Hi Xinyu,
  Thank you for sending me screenshots on your parameters. Can you please confirm that the status of the auto shut off level on the FDTD result view is 2? As in this example:
  
  Kind Regds,
  Niki
- November 24, 2023 at 2:38 pm
  
  Xinyu Liu
  Subscriber
  
  the status is 1
- November 24, 2023 at 2:41 pm
  
  Niki Papachristou
  Ansys Employee
  
  Hi Xinyu,
  This means that you simulation has not ended properly, I would suggest to increase the simulation time:
  Kind Regards,
  Niki
- November 24, 2023 at 4:19 pm
  
  Xinyu Liu
  Subscriber
  
  Hi
  Before, the simulation time for FDTD was 3000 fs and actually I thought it was already enough. Then I tried 30000 fs and the reflection is still over 1. Do you think I need to increase it more?
- November 24, 2023 at 4:30 pm
  
  Xinyu Liu
  Subscriber
  
  BTW, the status now is 2. Therefore, I think the simulation time is enough.
- November 27, 2023 at 9:08 am
  
  Niki Papachristou
  Ansys Employee
  
  Hi Xinyu,
  Thank you for your reply. Another common reason is the boundary conditions. What type of boundaries condition do you have?
  Kind Regards,
  Niki
- November 27, 2023 at 2:18 pm
  
  Xinyu Liu
  Subscriber
  
  Hi Niki,
  For FDTD, x&y uses Periodic and z uses PML(step angle).
- November 27, 2023 at 2:36 pm
  
  Niki Papachristou
  Ansys Employee
  
  Hi Xinyu,
  It might be worth trying PML and adding some layers. However, this is hard to say without knowing your simulation. Can you send some screenshot of the structure?
  Kind Regards,
  Niki
- November 27, 2023 at 2:42 pm
  
  Xinyu Liu
  Subscriber
  
  Hi Niki,
  The structure is somehow like this picture.
  Best,
  Xinyu
- November 27, 2023 at 2:59 pm
  
  Niki Papachristou
  Ansys Employee
  
  Hi Xinyu,
  I was hoping for a screenshot from your simulation. Nevertheless, try the suggestion on PML layers. Also you can find more helpful instructions here:
  Transmission Results Greater Than One
  Kind Regards,
  Niki
- November 27, 2023 at 3:10 pm
  
  Xinyu Liu
  Subscriber
  
  Do you mean this screenshot? Because all my layers use objective defined dielectric, the colour is all the same.

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