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Normalized transmission does not reach to 1 at resonant wavelength

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(joined February 2021)
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Dear Sir/Madam

I wish to record the response of the designed device for various input wavelengths. For this purpose the normalized transmission v/s wavelength is required at the output port.

Basically designed device is resonant cavity structure which has to show normalized transmission of value nearly equal to 1 at resonant wavelength. This designed is taken from already published paper “Elimination of cross talk in waveguide intersections”.

A pulse centered at 1.5 um wavelength is launched through the input port. Normalized transmission v/s wavelength has been obtained through the observational line in analyzer file. Maximum normalized transmission is only 0.4 only at resonant wavelength. It has to be 1 nearly 1 at resonant wavelength.

Please comment where we are legging in this modeling.

For reference I am also attaching design file.

Thanking You

Regards

man mohan gupta

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Responses (5):

    • #69966
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      Man Mohan Gupta
      Participant

      Dear Sir/Madam

      I wish to record the response of the designed device for various input wavelengths. For this purpose the normalized transmission v/s wavelength is required at the output port.

      Basically designed device is resonant cavity structure which has to show normalized transmission of value nearly equal to 1 at resonant wavelength. This designed is taken from already published paper “Elimination of cross talk in waveguide intersections”.

      A pulse centered at 1.5 um wavelength is launched through the input port. Normalized transmission v/s wavelength has been obtained through the observational line in analyzer file. Maximum normalized transmission is only 0.4 only at resonant wavelength. It has to be 1 nearly 1 at resonant wavelength.

      Please comment where we are legging in this modeling.

      For reference I am also attaching design file.

      Thanking You

      Regards

      man mohan gupta

      Attachments:
    • #70023
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      Scott Newman
      Moderator

      Looking at the design all seems relatively well configured. I do notice you have the simulation set to run until you tell it to stop. Without the information regarding how many time steps you ran it is difficult to comment. The reason for this is that with a resonant structure it is critical to get the power out of the resonator and if you do not run the simulation long enough you will not get the expected result.

      Do you have a screen shot of the time domain captured by the observation point?

      Scott

    • #70059
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      Man Mohan Gupta
      Participant

      Dear Scott,

      As per your suggestion, I have run the simulation for sufficiently long time. Maximum output transmission obtained for the design is 0.52 only. It is ideally to be 1 at resonant wavelength.

      I am attaching the time response and normalized transmission spectrum of the design.

      Thanking You

      Regard

      Man Mohan Gupta

      Attachments:
    • #70078
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      Scott Newman
      Moderator

      The problem you are dealing with is you are not normalizing / setting up the simulation correctly. Note that your Gaussian has a half-width of about 1.3 but the waveguide section of your structure is only about 0.5? Which means any field component that does not couple into the waveguide is reflected at the PhC interface. You are not getting a power of 1 because not all the power is getting coupled into that waveguide.

      Scott

    • #70082
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      Man Mohan Gupta
      Participant

      Dear Scott

      Thanks

      Can you let us know that what value to be chosen for the width of the gaussian pulse in order to get the normalized transmission 1? What is the criteria to select the width of the gaussian pulse?

      Thanks and regards

      Man Mohan Gupta

    • #70099
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      Scott Newman
      Moderator

      There is no single answer to this and it depends on what you are attempting to demonstrate.

      1. The efficiency of coupling a Gaussian beam coupling into the entire structure?
      2. The efficiency of the structure once the signal is in the photonic crystal structure.

      If it is the Gaussian coupling you place the source outside of the structure and the transmission you are measuring is what you get. However, you should realize that a Gaussian beam will not couple into this structure with anywhere near 100% efficiency so you should not be expecting a Transmission of 1.

      If it is just to demonstrate that the structure efficiently propagates the signal you could leave your setup as is and then use 2 observation lines. One is your transmission line left as is while the other should be the same and located towards the beginning of the structure. What you could then do is export the power spectra from the two and manually normalize the output spectrum by the input spectrum. I have done a quick test of this and you get normalized powers around 1 after some post processing.

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