Photonics

Photonics

Resonance wavelength of ring resonator is shifted with changing wavelength start of light source.

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    • HodaRezaei12
      Subscriber

      Hi, I designed a ring resonator in VarFDTD. The problem in my simulation is that when I change the wavelength start of the input light (Mode source) the resonance wavelength shift as well.  I want the resonance wavelength to be fixed even changing the light source range. I uploaded here a ring resonator with a 5 um radius (My project is designed with a 9 um radius that has this problem too), PML is large enough, and the simulation was run with the following setting: Mesh accuracy 6, Conformal Variant 1, PML type is set to Stabilized 32 layer, Wavelength domain in Mode source, 4000 monitor frequency point. I was wondering if help me to find what reason makes the resonance wavelength shift.

      All the settings in the uploaded project are changed since I could not upload it here.

    • Guilin Sun
      Ansys Employee
      Minor change of resonate frequency is normal when you change the wavelength start due to FDTD's dicretization. More specific, the resonate frequency may change on the mesh size. In general, for most dispersive or non dispersive materials, it is the "wavelength start" that determines the actual meshing size. More general, the simulation accuracy depends on the mesh size. This is why we suggest users to use coarse mesh to get rough result quickly, and then using finder mesh to improve the accuracy later, provided other settings such as PML thickness also change accordingly to have the best performance. This is the convergence test. Please refer this link https://support.lumerical.com/hc/en-us/articles/360034915833-Convergence-testing-process-for-FDTD-simulations


    • HodaRezaei12
      Subscriber
      Hi, thanks so much for the reply. I adjusted the optimum mesh which made a minor change of resonate frequency. I studied the mentioned link as well, I wanted to sweep the PML layers, PML distance, and mesh accuracy in VARFDTD. Whereas I don't know which parameter should be selected to sweep the same figure as the page mentioned. I appreciate you for the help.
    • Guilin Sun
      Ansys Employee
      Please note that all the parameters you mentioned may affect the result, so even if you sweep them it does not guarantee the accuracy for another device simulation. In addition, those parameters will need to be nested-sweeps . However there are parameter combinations which are wasted" for example, you use higher mesh accuracy but fewer PML layers and smaller PML distances. They are knowingly not effective for PML performance. Considering varFDTD is a variational method and its accuracy should be verified by 3D FDTD, I would suggest that you do the following:
      1: choose PML at least half wavelength
      2: roughly measure the PML thickness about half wavelength. You can estimate the thickness by definition of mesh accuracy: mesh accuracy 2 means 1/10 of the smallest wavelength INSIDE the material;
      3: sweep mesh accuracy only (2,3,4 should be enough)
      Please try those modification for varFDTD, and then use 3D FDTD to verify if the result is acceptable from varFDTD.
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