Negative Reflection Problem

TAGGED: fdtd, Lumerical-FDTD, photonics, reflection

- April 13, 2022 at 7:19 am
  
  mm_candela
  Subscriber
- April 13, 2022 at 5:39 pm
  
  gsun
  Ansys Employee
  
  This is a frequently asked question, as Lumerical calculates the "transmission" by definition, and defines the positive value when the energy flow is along the positive axis direction, and the negative value when light travels along the negative axis direction for some purposes. The calculation is here: transmission - Script command the sign of "transmission" is the same as the Poynting vector, as the monitor "surface normal" is always positive.
  As you know the power transmission is always positive. So in Visualizer please choose "-Re" instead of the default Re, and in scripting please add a negative sign in front of the "transmission" when the energy flow is towards negative axis direction. I do not suggest to use absolute operation as it may hide some potential is sues.
- April 13, 2022 at 5:40 pm
  
  gsun
  Ansys Employee
  
  BTW: Lumerical has a dedicated forum here: Photonics ÔÇö Ansys Learning Forum Please post your questions there later. Thank you!
- April 14, 2022 at 7:44 pm
  
  mm_candela
  Subscriber
  
  Thanks for your answer, but I don't understand. When I do -re and "-" in transmission script I get this shape. Here transmission appears instead of reflectance. But what I want is zero reflection at approximately 5.8 microns. So I absorb perfectly at that wavelength. How can I get this?
- April 16, 2022 at 9:17 pm
  
  gsun
  Ansys Employee
  
  The software its self uses "transmission" in general, it can be reflectance or transmittance. You can determine if it is R or T.
  To achieve zero reflection at approximately 5.8 microns, you will need to optimize your device, which is another topic. Please refer
  sweep : Parameter sweep utility - Lumerical Support
  optimization: Optimization utility - Lumerical Support
  Please write a new post at the Photonics Forum
  Photonics ÔÇö Ansys Learning Forum
  if you have questions.

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