Learning Forum

[mm_candela]

[Guilin Sun]

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.

[Guilin Sun]

BTW: Lumerical has a dedicated forum here: Photonics ÔÇö Ansys Learning Forum Please post your questions there later. Thank you!

[mm_candela]

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?

[Guilin Sun]

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.