Ansys Insight: Why my simulation result is different from published paper or experiment?

    • Guilin Sun
      Ansys Employee
      This is a commonly asked question from my experience. In the early years, some users wanted to compare simulation results with those obtained from other simulation tools, and in recent years many users want to compare the published results using Lumerical tools by his own simulation. Comparison gives you more confidence, yet it has some challenges.

      Usually the published papers chose the best simulated results, with many simulations of different settings. For new users, and even for those experienced users who used other tools before using Lumerical tools, due to some unique features and designs of the software, they will need some time to be familiar with the software and settings, before obtaining reliable simulation results.

      Here is a brief list of points you should check:
      1. the geometrical parameters
      2. the mesh orders to properly create the actual geometry. Pay close attention when some geometries have overlaps.
      3. the mesh accuracy and/or override mesh can (well) resolve the geometry? in most cases your mesh is not exactly the same as the published results. Some structures are more sensitive to mesh size than others. However, for your initial test, you do not need to duplicate the exact result, see comment later.
      4. Simulation region or volume: too close the PML to the structure can cause some problems, if it does not diverge.
      5. Material models: is it the simple analytical Drude, Lorentz model, or measured data? does the measured data agree well with our database (we use measured data from popular references). Is the simulation material property the same as the real material used in device under test?
      6. material fitting: measured data have errors, check if the fitting is proper: rms error, artificial peaks?
      7. make sure source type and polarization are correct
      8. source pulse length (and offset) are proper
      9. source’s location is proper
      10. Boundary conditions match with source type (and structure symmetry)
      11. PML type and number of layers (and thickness) as well as locations are proper. In general PML should be located in uniform mesh region
      12. mesh refinement: in general we recommend the Conformal Variant 0. more information is here
      13. Simulation time is long enough and autoshutoff min is small enough to make sure the em energy decays sufficiently. This is in particular important for transmission peak values.
      14. does the grating-like structure have higher-orders of diffraction? the transmission monitor gives the total transmission.

      In my opinion, if you can roughly get similar result with the publication, then the basic settings are almost correct. To get well-agreed result, more work of retuning the settings needs to be done. Further more, converging test may be needed, which is complicated:

      In addition, no all the papers gave all the necessary data, including device parameters, material models, and simulation settings, which lead to more challenge for duplication. and sometimes, the data given in the paper is not exactly the data they used in the simulation, due to a number of reasons.

      Some papers used other algorithms, and their data is good for their algorithms, but maybe not good for Lumerical tools.

      In other cases, the papers gave vague description about their devices. You will need to use your common sense to figure it out the correct parameters.
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