Ansys Employee

Hello, in time domain simulations, the optical signals have a carrier frequency called the channel frequency. When you have two sources, the channel frequency will be the average of the source frequencies. So when you change the CWL frequency, the carrier frequency changes. The TWLM model might change with a different channel frequency, which is why the TWLM behaviour is changing. 

You can keep the channel frequency fixed by changing the "sample mode frequency band" property of the Root Element to "single" then manually selecting the channel frequency with the "sample mode center frequency" property: