How to use the waveguide apodization option of the TWLM Interconnect Element?

DickDick Member Posts: 1

Dear Ansys/Lumerical team,

The TWLM Element, in INTERCONNECT from Lumerical, has an option to add apodization to the grating for a DFB laser (Waveguide/Apodization Properties). Along with a couple of predefined apodization functions, it also offers the option of implementing a custom apodization function.

My question are:

-How do I interpret the predefined functions (along with the apodization parameter); meaning, how do these functions actually change the grating and can I visualize this new grating profile? (If I find a favorable configuration, I will need to translate this to a mask design.)

-If I were to go for a custom apodization function, I would need to define this custom function in a *.dat file which has to be imported into the element, right? Do you have an example on the format of such a file? (Say for example for a symmetric linear profile: grating strength maximum at both facets and linearly declining towards the center of the cavity.)

Kind regards,

Dick van den Goor (student)


  • GWANGGWANG Posts: 99Ansys Employee
    edited March 17

    Hi Dick,

    Regarding your questions:

    1. The apodized Bragg grating have gradually changing along the grating structure, hence instead of having periodic square kind of refractive index changing, with apodization, the refractive index changing has an envelop based on the apodization type. For example, the Gaussian apodized grating has the index changing envelop with a Gaussian shape. Then in the equation for the apodization parameter, the apodizaiton profile T(z) defines the envelop of the apodization, with z being axis of the grating length.
    2. Yes you can define the apodization profile in the file. The model comes with a ffew of the most common types of apodizations like Gaussin and sinc type. If you want to define your own type which is not in the list provided, you can define the profile T(z) in the file and upload it. In the file you will need to define the transmission versus the grating length z.
  • DickDick Posts: 2Member

    Hello Gwang,


    Thank you for your response! If I may expand a little bit:

    -Is z, from T(z), normalized or is it the length in meters? And if it is not normalized, could I invoke the function getnamed(“TWLM_1”, “length”) in my profile *.dat file to normalize it myself?

    -Similarly, is the transmission normalized? Thus would T(z)=1 be the function form of the uniform profile?

    -If I would write the custom apodization profile as:

    ,where I assume that the cavity length and transmission are normalized, thus z ranges from 0 to 1. Will the effective top view of my grating than be something like:

    Which for our 1D simulation tool would be the same as:

    Or, because you said: “…hence instead of having periodic square kind of refractive index changing, with apodization, the refractive index changing has an envelop based on the apodization type”, will it effectively be something like:

    -Would you recommend me to write the *.dat file in the Lumerical script editor? (I remember that my custom gain files for the TWLM element sometimes would not be accepted. I guess this is due to an illegal space or tab in the document which makes it fail Lumerical's upload check.)

    -To be sure, do you maybe have an example *.dat file?

    -Lastly, you say that Gaussian and Sinc type profiles are common for apodization. Could you be so kind to direct me to work which uses these as their apodizatino profile? I haven’t done any extensive search yet, so if you know any papers, this would greatly help me!

  • GWANGGWANG Posts: 99Ansys Employee

    Hi Dick,

    You are absolutely right that the length is the normalized length. It requires the normalized length versus apodization parameter values data, in two columns. It can read in the .dat file. And I believe the index would be the first one as you attached.

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