Photonics

Photonics

FDTD Simulation bandwidth settings

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    • cohen26
      Subscriber

      Hi,


      I am trying to perform an FDTD simulation and get the response for a single wavelength. If I set my min/max wavelength to the same value, I notice that the global source still injects a pulse with finite bandwidth. As this is a time domain method, this makes sense to me. However, do these settings result in any simulation artifacts? I want to make sure the results are accurate for the single wavelength I am interested in.


      Thanks!

    • Guilin Sun
      Ansys Employee
      Yes, you are right that even though you specify a single wavelength, the time domain method still injects a pulse which is broadband. The single wavelength setting at the source is just to inform the DFT monitors to record only one specified frequency.
      To know if there is any artifacts or the simulation time is long enough, it is better to record broadband result for DFT monitors, which you can simply choose to override the global settings of the monitor and not "use source limit", then specify the wavelength range:

      This can be helpful in case the wavelength you choose is at strong resonance. With broadband result, you can check if the result, eg, transmission curve is smooth or not, in particular around the wavelength you are interested in. This bandwidth can be relatively small, and the monitor can record fewer frequency points.

    • cohen26
      Subscriber
      I see, thank you. For single wavelength, does the material fit get used within the bandwidth of the pulse? what if you don't have a material fit?
    • Guilin Sun
      Ansys Employee
      yes, whatever the material fit will be used in simulation, so the result at other wavelengths may not be as accurate as a better fit. If you set wavelength a single value, with fitting the software will use the default fitting. Because you are only interested in that specific wavelength, you do not case the accuracy of results at other wavelengths, but only to check if the result is smooth over the bandwidth, to avoid that case where that wavelength is at the resonance and needs much longer simulation time to get accurate result. For more information, please refer this https://forum.ansys.com/discussion/25276/simulation-time-and-frequency-domain-monitors Please note this is just a precaution. you may not need to do this.
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