Photonics

Photonics

About time monitor and group delay measurement

    • berkay.neseli
      Subscriber

      Hello,

      I am working on a device which can give high group delay and group index. To measure the delay, I am using a time monitor and the script given in this link https://optics.ansys.com/hc/en-us/articles/360042800113-Group-delay-analysis. I am using 2D topology optimization for now and then I will move to 3D but I have some questions.

      When the optimization finishes, transmission monitor (fom) is close to the structure. If I put the time monitor at the same place with fom monitor and then move it further away, the results are different. Which is the correct setup, closer to the structure or further from it? Does the script in the link works for inverse designed structures as well? Finally, I get some sharp dips resulting in negative group index and delay values but then they are followed by a sharp increase to the positive region. Is that expected or has a physical explanation?

      Thank you.

    • Guilin Sun
      Ansys Employee

      As long as you can get the result you want, this method should work.

      As you know, this method uses the fundamental definition to get the group velocity. and the time monitor should be located where there is only one mode, since the group velocity is associated with a single mode. Otherwise it may lose its physical meaning. You can use mode expansion monitor, or port to decopose the modes at that location and see if there are other modes there.

      Since it is from the fundamental definition, you will need to know if anything violates the assumption for the definition. You may need to simulate longer, use the proper last section of the time signal. 

       

       

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