Photonics

Photonics

NanoTaper Simulation FDTD, varFDTD

    • vdhurgude3
      Subscriber

      Hi,

      Can someone create a post or an article for photonic nanotaper simulation?

    • Guilin Sun
      Ansys Employee

      You can write a post for ay questions, or if you have peers with same interest, you may create a Forum Feed and invite them for discussion.

      For tapers, we have examples online:

      Linear waveguide taper 

      Polarization converter using a tapered waveguide

      Curved waveguide taper (varFDTD and FDTD) 

      HAMR - tapered waveguide

      Please indicate which solver you are using and what the problem you have.

    • vdhurgude3
      Subscriber

      Hi,

       

      I have a doubt about taper simulation. I am doing 3D FDTD simulation, should I use mode source or Gaussian Beam source. With mode source I get high efficiency as compared to Gaussian Beam source. What is the correct source?

    • Guilin Sun
      Ansys Employee

      Taper is a waveguade. It is nature to use mode source, or port which has all necessary monitors. Please note that you need PML to truncate the taper, or other input/output waveguide to avoid limited length taper which is a cavity and has reflections.

      You can also use EME, which is easily optimize the taper length.

      • vdhurgude3
        Subscriber

        Hi,

        Thanks for your reply. Actually, the taper i designed is nanotaper. One end has extremely small width and another end has a waveguide width. My goal is to do edge coupling from fiber to the smaller end of the taper. I used gaussian source  to create mode profile coming out of the the fiber tip. With gaussian source my efficiency is extremely low. With mode source transmission efficiency is around 80%. So please guide correctly with existing examples for taper design

    • Guilin Sun
      Ansys Employee

      Then you should use the fiber mode. I guess it might be due to polarization mis-match with Gaussian. In addition, Gaussian beam is an approximation of the fiber mode. If the fiber is too large to be included in the simulation, you can first simulate the fiber mode and record data (most likely in air or a uniform material) and then import it as source for edge coupling. However, it eliminates the possible reflection from the fiber end surface, which should be small.

      https://optics.ansys.com/hc/en-us/articles/360034383034-Using-monitor-data-to-define-the-spatial-field-profile-of-a-source-in-FDTD

    • vdhurgude3
      Subscriber

      Hi Guilin,

      Thanks for your reply. Before doing FDTD simulation, I did fiber to waveguide edge coupling. From fiber to taper end edge coupling, I get efficiency of 90% between TM mode of fiber and first TM mode of the taper end.

       

      So for FDTD simulation, should I take mode source into account with first TM mode simulation at the start of the taper rather taking Gaussian source? Will it be a correct approach?

    • Guilin Sun
      Ansys Employee

      Is there any gap between the fiber and the edge coupler?

      a mode can only be supported inside a waveguide or fiber.

      If the field needs a certain propagation distance before coupling, you can use the import source from the first simulation. If they are end-to-end coupling without gap, it is better to have the fiber in the simulation.

      I do not know the configuration of your device so just give you some general suggestions.

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