Photonics

Photonics

Lumerical FDTD – Is it feasible to use mode expansion monitor for plasmonic waveguides?

    • iplikcioglu
      Subscriber

      Hello,

      I'm trying to extract the complex reflection coefficient due to a discontinuity on a plasmonic waveguide (insulator-metal-insulator structure). I was wondering whether the mode expansion monitor would still work in this case to extract the complex transmission coefficients (both forward/backward) of the fundamental long-range mode.

      Additionally, Lumerical Support document states that there are two different expansion script functions (expand and expand2) with the latter being for the general mode profiles (absorbing or non-absorbing). Which one does the mode expansion monitor use? (e.g. does it adapt based on the loss profile?) Also how can I use these functions with the mode data of a single monitor? Thanks in advance.

    • Guilin Sun
      Ansys Employee
      Hi, I believe the mode expansion monitor uses "expand", which uses conjugate operation. The difference of the two functions is to use conjugate or not. When E and H are in phase, conjugate operation will lead to mode power N and N* the same, which is mostly used. Their results will have a difference of phase. When the modes are lossy, you can use either of them. Depending on your purpose, there might be further processing, such as reconstruct the fields in the DFT monitor with a few modes, or get the S parameters.
    • iplikcioglu
      Subscriber
      Thanks for your response. I also have one more question: Is it possible to use the calculated mode fields (from the source) in expand or expand2 functions? From the source d-card, I'm getting the error "the necessary data to perform an overlap calculation was missing." I presume this is because the modal fields are stored in polar notation in the source. Is it possible to bypass this? Thanks a lot.
    • Guilin Sun
      Ansys Employee
      This is a different question. I strongly suggest to create a new post later, so we will maintain the convention of "one posted question and one answer", which will be helpful for other users.
      To do an overlap calculation, you will need to save the monitor data on a d-card. I think this issue is not related to the SPP mode. If the two dcards have different orientations, eg, one is in XY pane and the other is in YZ plane, it will give this error.
      In addition, monitor has set a number of frequency points, whereas the source is diffent , so you will not be able to do the overlap.

      If you really want to calculate their overlap, please create your own script.

      I tested both FDE and FDTD, using the copydcard, both work.
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