The Q factor in SWG ring resonator (FDTD) is out of the range of wavelength

Dear Sir /Madam

I have put Q analyzer in my structure and I have set the wavelength in source and monitor (1.5 to 1.6nm)
but the Q factor result is between 1.8 to 1.9 nm, I want to know what is the reason and how can I solve this problem I have tried both these solution but I couldn’t solve it.
Thank you for your kind help

The Q analysis group uses time domain monitors and uses the fftw (low Q analysis) or fft (high Q analysis) script command to perform the Fourier transform of the time domain data to get the frequency-domain data with peaks at the resonant frequencies. Since the source uses a broadband pulse in the time-domain by default, it will include a wider range than the specified range of 1500-1600 nm. One way you could limit the range is by using a more narrowband source, and this can be done by un-checking the “optimize for short pulse” option discussed on this page:

Another method which would be more complicated is to go into the analysis script of the Q analysis group and change it to use the czt script command where you can specify the frequency range of the transform instead of using fft or fftw script commands:

Hi @elnaz,

Can you eventually upload your simulation file so we can have a look? To make sure the file isn’t too big, please save it in layout mode. After you ran the simulation, you can get back to layout mode by clicking on the “Layout” button: