Photonics

Photonics

What is reason of the ripple in the transmission spectrum of the edge coupler

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    • liyaqian
      Subscriber

      An edge coupler is simulated by EME. The main structure is an inverse SiN taper and 8um-thick SiON cladding. The boundary conditions are PML, except that the Y miax is Anti-symmetric. I do not know why the ripple of the transmission spectrum of the edge coupler is so serious. And what is the reason for the dip at 1430nm? Could you give me some advice? Thank you very much. Look forward to your reply.

    • Guilin Sun
      Ansys Employee

      The dB scale amplifies the ripple. Seldomly EME result shows ripples. I guess you used the "wavelength sweep" utility, which simplifies the sweep with only wavelength change but not the neff and mode profile. To verify, you can also simulate the shortest and longest wavelengths and compare with the sweep result. Usually the initial simulation uses the center wavelength.

      Please check the linear scale first.

      You may need to compare the settings with the online example and check the differences and reasons. With very limited information it is hard to know the exact causes.

    • liyaqian
      Subscriber

      Yes, I did use "wavelength sweep". As for your advice, I set EME solver with different wavelength and then do wavelength sweep. Here are the results of different center wavelength.

      Which result is resonable? I think that every independent center wavelength is resonable, rather than the sweep result of a series of wavelength. Besides, the dB scale is changed with the percent scale and the ripple is still serious, for an edge coupler.
      k (in n,k) of SiN is 0, so we do not consider dispersion. The boundary conditions and the input source are the same with the example. Hope for your reply,

    • Guilin Sun
      Ansys Employee

      The built-in wavelength sweep is simplified method as mentioned previously. It can be good when the mode dispersion is small, or the bandwidth is small. In your case it seems the bandwidth is large, and I would guess the neff dispersion is large, which causes this problem.

      You may try to use script to do the wavelength sweep which should give you better result. The price you pay is significantly long simulaiton time. If you use 100 frequency points, it will be 100 times slower.

       

      In addition, you may compare the mode profiles at shorter wavelength and the longer wavelength, as well as neff since you have the data.

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