Q factor

    • dhiraj_177

      I have designed a ring resonator using photonic crystal. In one design one ring is pesent & in second design two ring is present. output of first ring becomes source for second ring. Now when i calculate Q factor in single ring it is 882 but in double ring it comes 175 means it is reduced but theoretically it should be increased which is verified by transmission curve also.

      So my question is how software is calculated Q factor in case of double ring.

    • Guilin Sun
      Ansys Employee

      I do not know where you place the time monitors? have you set proper simulation time to have the second ring coupled with resonance?

      Please check the settings. When the couping from ring 1 to ring 2 is large, it can reduce its own resonance. You will need to optimize the coupling gap.

      Please note that we have two methods to calculate Q:

      1: frequency domain method. The simulation is run long enough to get accurate transmission, where you can calculate Q=f/delta_f from the resonance

      2: time domain method. It has fft method and findresonance method. Both do not need long simulation time, since they can use a short section of the time signal to get the result.

      Please refer https://optics.ansys.com/hc/en-us/articles/360041611774-Quality-factor-calculations-for-a-resonant-cavity

      Please check the analysis group you are using to get more information. You may need iterative simulations to get more accurate result:

      from the first simulation you get the resonant frequency. Then you add a profile monitor of the resonant wavelength to find the peaks of intensity. Then move the dipoles and time monitors to the peak locations.

      Or you can use several analysis groups and place them in different locations. You can choose the largest Q as the result. If you use fft method, please make sure the curve  log(E) vs time is a stright line.




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