Home Forums SYSTEM clear constellation

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    • #14986
      boldoo
      Participant

      how to draw pure constellation in I-Q modulator. Mine is always so many spots.

    • #15022
      Damian Marek
      Participant

      Make sure your oscillator (CW Laser ) has a small linewidth. For a perfect system set it to 0, realistically I think nowadays a linewidth of 0.1 MHz is not unreasonable.

      Good luck!

    • #15058
      boldoo
      Participant

      Hi Damian,

      you mean we should keep 0.1MHz at CW laser?

      my schema has CW laser with 0.1MHz. I will add fiber and receiver to my schema.

      • #15077
        Damian Marek
        Participant

        Phase noise is what causes that wander of the constellation diagram, so using a laser with a smaller line width will eliminate that problem. Try a linewidth of 0 and you will get “perfect” results, although physically it might not be accurate.

    • #15177
      Alessandro Festa
      Participant

      Is you constellation after the signal passes in an optical system?

    • #15180
      boldoo
      Participant

      No, just after modulation. I didn’t add amplifier and fiber.

      But actually after added fiber(50km), my constellation became to just crowded thing in central. how to fix it?

    • #15184
      boldoo
      Participant

      I’m trying to apply 16QAM.

      after transmitter, connected to amplifier and Gaussian filter then 50km fiber, then amplifier and filter.

      After second filter, I checked 16QAM coherent Receiver and Constellation Visulaizer.

      but result is like attached.

      • #15210
        Damian Marek
        Participant

        It should be possible to transmit the signal over 50 km of fiber with low distortion of the constellation. Maybe you have a filter or component that is set to the wrong values. Can you attach your project file?

    • #15339
      boldoo
      Participant

      Hi Damian,

      please check attached project. i created 16APSK signal after modulator. But After fiber and amplifier, constellation is very bad. is there any way to keep constellation as possible? what components was wrong ?

      Attachments:
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