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setting up simulation parameters in FDTD

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(joined April 2014)
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Hi there,
I am working on this simple layout. it does work but simple Si 3.45 index is giving some oscillations at lower wavelengths and I have tried almost everything to fix this. but didn’t get it. can anyone please help me.

Responses (19):

    • #11744
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      perveen akhter
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      Hi there,
      I am working on this simple layout. it does work but simple Si 3.45 index is giving some oscillations at lower wavelengths and I have tried almost everything to fix this. but didn’t get it. can anyone please help me.

    • #11824
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      Aurelien Duval
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      Hi Perveen,

      I’ve tried to run your example. However I don’t really anything wrong with it. Could you be more specific, for example a plot of the oscillations?

      Thanks

      Aurelien

    • #11825
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      perveen akhter
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      Thanks Aurelien for your reply.
      the problem is that it doesn’t give a constant reflection,but with variations between 0.3 and 0.34 probably due to interference. so I was trying to get a more smoother reflection ,coz I plan to add metal nanoparticles on this subs and the plasmoinc effect is not as clear as it should be coz of this reflection interference. I am trying hard to find best APML no. of layers to minimize this.
      I hope you got my question.
      waiting for reply.
      Perveen.

    • #11826
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      Aurelien Duval
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      Hi, with the project file you attached, I get 10^-18 W on the reflection observation area! It’s the computer’s way of saying 0.
      Could you be more specific, for example giving a plot of the oscillations?

      Which version of OptiFDTD are you using?

      Thank you

      Aurelien

    • #11827
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      perveen akhter
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      please find the attached reflection plot. I want to get a smooth/constant reflecion.
      we have version 9.
      thanks,
      Perveen.

      Attachments:
    • #11830
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      Aurelien Duval
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      Ok, I understand better, thank you.

      You should increase the number of PML layers to absorb more incoming light. For example with 64 layers, almost all oscillations are gone.

    • #11831
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      perveen akhter
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      did you change anything else too. coz I am still getting the same results. also I am using APML boundary conditions, not PML?
      and no. of APML layer coefficients is 30.
      any suggestions?
      thanks.

    • #11867
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      Aurelien Duval
      Participant

      I cannot easily tell you if the inner workings or the simulation engine changed for that particular point between version 9 and 12.
      Like I said, the more layers, the less reflections you will get, but the slowest the simulation will run.

    • #12054
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      perveen akhter
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      Hi there,
      it seems that for a layout which is working fine, changing xy wafer dimestions changes the results a lot, keeping same mesh size and even increasing the timesteps doesn’t produce the same restuls as original layout. how to compensate the wafer size effects?
      thanks.

    • #15140
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      perveen akhter
      Participant

      Hi there,
      it seems that for a layout which is working fine, changing xy wafer dimestions changes the results a lot, keeping same mesh size and even increasing the timesteps doesn’t produce the same restuls as original layout. how to compensate the wafer size effects?
      thanks.

    • #15142
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      Damian Marek
      Participant

      Do you have a more recent project file? I could take a look.

    • #15145
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      perveen akhter
      Participant

      please find the attached layout and the results. I started with gold np sample# 52 and change the size n getting a lot of noisy peaks.
      thanks,
      Perveen.

      • #15152
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        Damian Marek
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        Ah, the first thing I notice is that you are using periodic boundary conditions for the x and y dimensions. When you modify the x and y; lengths you are effectively changing your periodic lattice, or the distance between nano-particles.

        • #15153
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          perveen akhter
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          so bigger wafer size, means larger distance betweeen particles, so no interaction, so I should get better results. but doesn’t work that way.

        • #15161
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          Damian Marek
          Participant

          Are you trying to simulate a periodic structure? If not I would suggest simply using absorbing boundary conditions on all boundaries and use a Gaussian spatial input instead of the rectangular.

        • #15196
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          perveen akhter
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          thanks, if you can send me a layout. or modify my layou n send to me. I am using version 9. thanks a lot.

        • #17095
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          perveen akhter
          Participant

          Hi Damien,
          I need your help with this layout simple thin film on si substrate with input at 45 deg. for some reasons I am getting negative absorption.
          attached is the layout and plot.
          thanks,
          Perveen.

        • #17120
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          Damian Marek
          Participant

          Hi Perveen,

          The silicon carbide material is defined with a positive imaginary part of the index of refraction. In engineering convention (and OptiFDTD convention) this means an amplifying medium, not a lossy one. You may want to change that to a negative imaginary part. This amplifying effect is what I assume is giving you a negative absorption.

          Regards

        • #17124
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          perveen akhter
          Participant

          still getting negative absorption. could this be coming from any interference coz of input angle being 45 deg????
          thanks,
          Perveen.

    • #15151
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      perveen akhter
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      first slide is for radius50 nm, second for 10 nm

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