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Evanscent coupling

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(joined April 2022)
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Hello,

I have been trying to simulate an evanescent wave coupler in optiBPM following the instruction from your manuel (Lesson 6).
When I tried to implement the X-coupler to my own fiber dimmensions I can’t observe any coupling in the results of my simulations.
Can you help me to figure out what is happening ?

Best regards,
Timothé Desbordes

Responses (5):

    • #70681
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      Hello,

      I have been trying to simulate an evanescent wave coupler in optiBPM following the instruction from your manuel (Lesson 6).
      When I tried to implement the X-coupler to my own fiber dimmensions I can’t observe any coupling in the results of my simulations.
      Can you help me to figure out what is happening ?

      Best regards,
      Timothé Desbordes

    • #70700
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      Scott Newman
      Moderator

      Hello Timothé,

      Can you please attach your design in question?

      Scott

    • #70703
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      Hello Scott,

      Thank you for your reply and help, here attached are the designs.

      I first tried with the “EvanescentWaveCoupling_phoenixFiber – Copy” design then tried to understand what was going on with the “EvCoupler” one which follows a similar design but without cladding.

      Best regards,
      Timothé DESBORDES

    • #70713
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      Scott Newman
      Moderator

      Hi Timothé,

      Looking at the mode of your fiber it is highly confined and your evanescent does not extend out past the silica core you have defined which means there is no overlap between it and the adjacent fiber. This can be confirmed by looking at the Optical Field Propagation within OptiBPM with the structure overlay turned on.

      Are you certain there is supposed to be evanescent field outside the fiber for this mode?

      Scott

      Attachments:
    • #70743
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      Hi Scott!

      I have been tinkering on the simulation starting from the “Lesson6_3dB_coupler” one more time, I took the file from your tutorials and using the same materials (Dielectrics and Channels) as the tutorial again I couldn’t observe any coupling were I must have seen some.
      I the attached file I removed the cladding at the coupling region but I couldn’t observe any change.
      What can I do to resolve this problem ?

      Best,
      Timothé

    • #70746
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      Scott Newman
      Moderator

      Less6_3dB_coupler.bpd as you have attached it has 2 issues:

      1. The example spaces the linear waveguides making the coupler at X = +/-3 um. You have set yours to +/- 4 um. If you make that correction you will see the coupling.
      2. In a couple of places at around the 470um and 530 points your have a waveguide coming from just before it (468) and right at it (470). They should both have the same value. The same is true at around the 530 um point.

      As for EvCouplingTwo.bpd the results look to me like they are going non-physical as you go around the bend. Based on your design this could be a couple of things that would require investigation:

      • You have the core and cladding separate due to the way we layout the 2D. You are using only the core as the propagation constant in your Global simulation settings. I would determine the mode of the whole waveguide and use that manually.
      • It is possible that the bend is too steep with the refractive index contrast. This would need investigation.
      • Possible convergence issue which would need to be investigated though this one is less likely versus the other two based on the field distribution.

      Scott

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