sweep using BFAST


how to run broadband angle sweep using BFAST ?


Dear @jasleenk

There are couple of posts that you can take a look at them:



When I change source setting to BFAST and run the file,it says BFAST settings are not stable because there is no value of ‘dt’ that can give the stable criteria. bfast angle sweep.log (2.3 KB)
BFAST angle sweep.fsp (17.7 KB)


Dear @jasleenk

This is because BFAST source is injecting light at an angle above the critical angle. In this case you will get a warning box saying: “Warning, your current BFAST settings are not stable because there is no value of dt that can meet the stability criteria. Please contact Lumerical Technical Support for more information”

This is explained in this post:

Injection above the critical angles for total internal reflection (TIR) is not allowed. There is no possible stable time step dt in this case. For example, injecting light at 50 degrees in glass that is incident on a glass/air interface is not stable. However, if you are injecting light in a lower index medium onto a higher index medium, then it is allowed. For example, if you are injecting light from glass onto a higher index substrate, such as silicon, then you can use BFAST – however, the value of “bfast alpha” should be set equal to the smallest refractive index used anywhere in your simulation.