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Bent Waveguide using FDE vs FDTD

    • Then Elango

      Hi Guys, this might be a long shot, but if anyone has info regarding the following will be helpful. I am new to this area of research. 

      1. What could be the possible dimensions of a waveguide. In my case, the material of my waveguide would be 1.62 (polymer), so I add this to the materials box and use it. The wavelength of the light is 1.55 um. On an average for SOI platforms- for  waveguides, 400nm x 220 nm are used as dimensions. Can I use the same? I tried to find the dimensions using FDE, as I need to simulate for fundamental TE00 mode, how can I do this? Because I was under an impression that we analyse the modes in FDE for a dimension in TE00 and simulate the dimension in FDTD. Is my understanding wrong?
      2. How to estimate the loss of a waveguide in FDTD? In FDE analysis, we can see when we calculate the modes: but where do we locate when we use FDTD. ?
      3. What does loss (dB/cm) imply? For more radius, we intend to get low loss, but the numerical value is higher for higher radius. Shouldn't higher radius have lower loss value?
      4. While using FDTD simulation, how to simulate a waveguide (or design a waveguide ) with varying radius  of curvature?   In the structures we have  a bent waveguide(90and 180 deg) but they are circular waveguide with constant radius of curvature. How to design a waveguide where there is a varying radius of curvature accurately? Should we alter the waveguide parameters by script as shown below? because i would want a waveguide with where the radius of curvature is different along the waveguide bend. 


      Any info on these would be much helpful!! Thanks guys!! :)


    • Guilin Sun
      Ansys Employee

      Usually the simulation volume should be larger than the device, except to use PML/peridoic BCs to truncate the device in purpose, such as infinitely large.

      You can find TE00 based on the TE polarization value, and also should be aware that TE/TM has two differfent definitions.

      A1: FDE is to analyze the mode properties, and FDTD has mode source/Port that uses FDE. So FDTD can be used to simulate waveguide devices

      A2: In FDTD, you can get the loss from a mode source or port. or

      you can set to use "user select" in "mode selection" and click "select mode", then the FDE interface will open


      A3: please visit

      A4: you have to create the bending waveguide first. Please refer the object library for "integrated optics". If you create your own, you may need to learn how to use the structure group, and script.


      We prefer to one-post one-reply. So please refer some online resources:

      and other online examples.


      and write one post for one question.


      • Then Elango

        apologize for the inconvenience , I will post one question only. Thank you

    • Then Elango

      Thank you very much for the help

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