Photonics – Chinese

Photonics – Chinese


    • Xiangrong

      Dear Ansys Team,

      I hope you are doing well.

      I am currently working on simulating a diamond-based photonic crystal cavity (PCC), H1 cavity, and am a beginner in using Lumerical software. We would like to achieve a higher Purcell factor to increase the single photon emission efficiency at the wavelength at 637nm, which is the zero-phonon line (ZPL) of NV- center. For the simulation settings, mesh accuracy is 2, boundary conditions are PML, and simulation time is 2000fs.


      My questions would be as below,

      1, Is it necessary to do the convergence test before running the simulation? I found some resources about this on the knowledge base, there are some sources of error, e.g., mesh size, mesh accuracy, PML layers, etc. If necessary, what parameters need to be considered in this case? And if I change the parameter of the PCC structure, such as radius, and lattice constant, do I need to do the convergence test once again? To what extent we could say the system is converged?

      2, I introduced an analysis group to calculate the resonance frequencies of the cavity and Q factor, which is randomly distributed but sometimes does not work. I could not find a reason for this. Besides, I added a time monitor in the system to visualize the spectrum and resonance. The spectrum is visible. For the resonances, it said failed to calculate results. Does it mean this structure is non-resonant? Would the analysis group and time monitor position affect the result?

      3, When is necessary to include the override mesh setting?

      4, If keep all the parameters the same, and just change the simulation dimension from 2 to 3, the Purcell factor result is not desirable and changes a lot.

      5, Sweep parameters. For example, in this task, we would like to increase the Purcell factor. It relates to parameters, which need to be optimized: radius, lattice constant, number of holes, and thickness. How to make use of sweep to find the optimum value for all parameters? 


      If there is some needed information missing in my description, please kindly let me know.

      Many thanks for your help in advance, and I look forward to hearing from you.


      Regards, Xiangrong


    • Guilin Sun
      Ansys Employee


      A1: it is not neccessary to do convergence for every design. Only do this for the promissing design.

      A2: you have to open the analysis group. open the analysis script, and run it. The error will be displayed so you will know what is the cause. Most likely one or more time monitors has no data, out side of the simulation region. This can be true when you use symmetry BCs.

      A3: override mesh is mostly used for resolving geometry details. I would suggest to have about 4~6 for moderate accuracy, 2~3 for low accuracy.

      Since the photonics crystal is supposed to be periodic, so you will need to make sure the lattice is discretely periodic, which can lead to better result. eg, you will see each hole is meshed the same.

      A4: if the simulation dimension changes the result, it means the original dimension is too small. You will need to make sure the PML is about half-wavelength away from the structure.

      It may also mean the Q analysis group or dipole cloude is not properly set. Actually such simulation will need iteration simulation: find the initial resonance wavelength, then add a monitor to monitor the field distribution for that wavelength. then move the dipole and time monitor to be in high intensity spots. This can give you a better result. You will need to repeat this.

      Make sure the silicon is embeded in a dielectric material, other than air, for practical reason.

      A5: sweep is to find the range of a parameter. I suggest to not sweep many points. Instead, iterating the parameter ranges to find the range of global optimization. then you can use optimization to get best result.

      Please note that the forum is for one-post one solution. So please post your most difficult quesiton once a time in one post. Once it is solved, post another question.



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