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Discontinuity at the boundary of the substrate and waveguide of AlN-on-sapphire

- September 20, 2024 at 9:20 pm
  
  Minming He
  Subscriber
  
  Hi,
  when I was simulating the AlN strip waveguide on sapphire substrate, I noticed that there is a discontinuity at the bottom of the waveguide. I input only one refractive index of 369nm for the material. I would like to know what might cause the discontinuity. Thank you!
- September 23, 2024 at 6:06 pm
  
  Guilin Sun
  Ansys Employee
  
  It is correct, since now you are plotting the total field. If you only plot the tangential field components it will be continuous. In the normal direction it is the displacement field that is continuous.
- September 23, 2024 at 8:31 pm
  
  Minming He
  Subscriber
  
  Thank you for you reply. I still have one question: according to this disagram, can I say that the power is leaking into the substrate?
- September 23, 2024 at 9:45 pm
  
  Minming He
  Subscriber
  
  Hi,
  I tried to simulate it again. This time, the Ez of TM mode still shows discontinuity:
- September 25, 2024 at 4:13 pm
  
  Guilin Sun
  Ansys Employee
  
  Ez is not continuous since it is normal to the boundary;
  When there is field inside the substrate, it does not necessarily mean leakage, of course depending on your definition of leakage. Usually when the substrate is lossy we can say leakage. You can calculate the loss inside the sub strate.

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