Home Forums SYSTEM CO-OFDM Architecture

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    • #14745
      alistu
      Participant

      In CO-OFDM transmitter, a 90degree phase shift is used (as indicated in the file attached which shows a block diagram of the system). Why has not this phase shift block been used in Optisystem sample file “Coherent Detection Optical OFDM system.osd”?

    • #14746
      alistu
      Participant

      And here is the block diagram of the CO-OFDM system simulated by Optisystem which does not contain the phase shifter.

      • #14815
        Damian Marek
        Participant

        Couldn’t see your attached pic of the block diagram. Can you try reattaching as a jpg or png?

        I may be able to guess at the answer though. Those X couplers used in the OptiSystem design actually cause a 90 degree phase shift when the input is coupled to the opposite output. The bottom branch of the transmitter will have a 90 degree phase shift compared to the upper branch.

    • #14767
      Ravil
      Participant

      Hi alistu, a phase shift is required block in OFDM to create orth. components. It is included in “Coherent detection” block. In my opinion, it should be placed after MZM.

    • #14768
      Ravil
      Participant

      Did you try to ‘run’ that scheme, by the way?

    • #14965
      alistu
      Participant

      Here is the block diagram of the system which was not attached.

    • #14968
      alistu
      Participant

      Yes, I have run it and it works.
      There has been used a phase shifter in the coherent detection block, which is according to the theory. But none in the transmitter…

      • #14997
        Damian Marek
        Participant

        Ok there is actually a 90 degree phase shift in the OptiSystem project layout, but it is incorporated into the X coupler. In the simulation (and also in physical X couplers) the signal that is coupled to the adjacent waveguide experiences a 90 degree phase shift. If you look at the transmitter and receiver you will see X couplers that incorporate this phase shift.

    • #15107
      alistu
      Participant

      That’s the point I hadn’t noticed. Thanks.

    • #15115
      Ravil
      Participant

      Thank you for the explanation Damain! Do you know the purpose of including Electrical Gain in one of the MZM arms at the transmitter?

      • #15135
        Damian Marek
        Participant

        The electrical gain is there to facilitate an efficient dual driven modulator. Each branch does not have to modulate the entire Vpi, only half of it.

        In a phase shift keying scheme then both branches would have the same amplitude.

    • #15116
      Ravil
      Participant

      Did anybody test this scheme for its max transmission capacity? (Just wandering…)

      • #15136
        Damian Marek
        Participant

        By max transmission capacity, do you mean max bit rate to maintain a certain BER?

    • #16814
      alistu
      Participant

      If by “capacity” you mean Bitrate-Distance product, I have tested it and to my surprise I could only achieve 10Gbps for 360km, which is much less than that of any other paper I’ve studied about CO-OFDM since 2007 (for example, in Alatawi’s 2013 master’s thesis at University of Denver, a system with 50Gbps for 6000km was achieved using Optisystem v.12 without exploiting any types of equalizers and so on). So I would also like to know if anyone has tested the system in this regard. Thanks in advance.

    • #17734
      alistu
      Participant

      How is receiver sensitivity considered in Optisystem coherent optical OFDM example discussed above? I believe there should be such a parameter in PIN photodetectors, but there isn’t. And sensitivity is not something that can be neglected. Can anyone help please?

      • #17743
        Damian Marek
        Participant

        The receiver sensitivity is not explicitly shown or set within the PIN Photodiode, as it depends on the users definition (which Q factor is chosen as the threshold). However, the noise and bandwidth which can be set within the Photodiode changes the sensitivity of the photodiode and a nice little example of this is found at this link:

        http://psut.edu.jo/sites/yazan/classes/Spring2010/MicrowaveLab/FExp4.pdf

        Let me know if this helps!

    • #17753
      alistu
      Participant

      Thanks a lot! I got what I needed to know.

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