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frequency separation in dual tone optical signal

(joined August 2015)
Participant

Hi all,
I want to transmit a dual tone or dual wavelength optical signal (i.e. the multiplexed one) through a standard single mode fiber, but when I transmit the signal it gets distorted because of various reasons such as dispersion, phase noise etc. so it would be very much helpful if anyone share his experience working in this field. Thannking you,

Regards,
Dhiman kakati

Responses (18):

    • #30874

      Hi all,
      I want to transmit a dual tone or dual wavelength optical signal (i.e. the multiplexed one) through a standard single mode fiber, but when I transmit the signal it gets distorted because of various reasons such as dispersion, phase noise etc. so it would be very much helpful if anyone share his experience working in this field. Thannking you,

      Regards,
      Dhiman kakati

    • #30881

      is it dependent on bitrate of the system if so what minimum frequency separation will be beneficial for 20 Gbps bit rate.

    • #30886
      Profile Photo
      Naazira Badar
      Participant

      Hi Dhiman

      Are you using a WDM MUX?

      Regards

      • #30969

        Hi Nazira, thank you for the response. though I mentioned about the wavelength multiplexing presently I am not using WDM multiplexure here in my case. I just created the dual tone signal in the electrical domain using two sine wave having different frequency for radio over fiber technology as in the attached snapshot and then applied to the Mach zehnder modulator to have the dual wavelength in the optical domain. please have a look into it.

        Regards

        +2
    • #30903

      Hi Dhiman

      Yes your system performance does depend on the bit rate.If you want your system to support a high capacity of 20 Gb/s you might need to use amplifiers in your design.
      If you are using a WDM MUX and DEMUX in your design.I suggest you to check the power level of your signal at the MUX and DEMUX outputs.You can use a spectrum analyser for the same.Depending on the drop you see at the output of the MUX you can set the required gain of your amplifiers accordingly.

      Regards

      +7
      • #30971

        Hi Fayiqa,

        Please refer to the above reply #30903 where I have attached the snapshot of the system of my design.

        I will definitely look into these parameters such as power level at the MUX and demux outputs as you have suggested and use amplifier to compensate for the signal attenuation. Thanks for the valuable hint.

        Regards,
        Dhiman

    • #31030
      Profile Photo
      alistu
      Participant

      Hi Dhiman,

      Can you please upload your OptiSystem design implementation if it is actually possible, this way, it could be easier to analyze the system and manipulate it if necessary to see if some changes had better be made to it and also to see how it can depend on the bit rate and so on. Thank you.

      Regards

    • #31063

      Hi Alistu,
      I am attaching herewith the design file, please have a look, I need to have a clear spectrum in optical domain so for this you are allowed to do any kind of modification. you can see the electrical frequency is quite clear in this context, i.e. dual wavelength.

      Regards,
      Dhiman

      Attachments:
      • #31085
        Profile Photo
        alistu
        Participant

        Hi Dhiman,

        Since the signal has not passed through the fiber yet, dispersion or other channel impairments do not affect the optical spectrum. I reduced the laser linewidth to 0.1 MHz (which is quite consistent with the commercially available low power lasers), and I believe the spectrum got obviously better. Please see if that is acceptable.

        Regards

    • #31099

      Hi Alistu,
      Thanks for the reply, you can see at the modulator output there are 5 noticeable peak in terms of wavelength. so clearly i need two peaks in optical spectrum also. I have attached herewith the snapshot of the same.

      Regards,
      Dhiman

      Attachments:
      • #31121
        Profile Photo
        alistu
        Participant

        Both in the screen shot you have attached and using RF spectrum analyzer in the implementation, more than two peaks are clearly visible. And since the signal is up-converted to the pass band, it is not strange to see more peaks. Besides, I put nonlinear effects of laser to zero and the optical spectrum just got more clear, keeping the same peaks. I suggest you evaluate the performance regarding BER to make it easier.

        Regards

        • #31128

          Hi Alistu,I am not getting the output as you have explained, please attach herewith the modified design file, that would be very much helpful. Yhanking you.

          Regards

        • #31131
          Profile Photo
          alistu
          Participant

          I am merely referring to RF spectrum analyzer (the one that has been used after the combiner). Or even the electrical signal you have attached in your former comment clearly shows what seems to be only two peaks consist of more small peaks that are close to each other. The only change I made to your design was to change the linewidth the way I mentioned.

        • #31544

          Hi Alistu,
          You are correct that there are two peaks in each frequency of the RF spectrum analyzer which is noticeable, is there any way to make one peak in each frequency of the Electrical domain.
          and I made the linewidth which I did not change before (forgot to do so). Thanking you.

          Regards,
          Dhiman

        • #31552
          Profile Photo
          alistu
          Participant

          You’re welcome. The signal is modulated with a frequency of 450 MHz by the quadrature modulator. So when it is up-converted again, two peaks form around the 10 GHz and also around 20 GHz new carrier frequency, each having a 450 MHz distance from the center carrier frequency. This is according to theory and nothing seems to be wrong about it.

          Regards

        • #31588

          Thanks alistu for making me clear, I tried making higher frquency such as 10 GHz then the separation increases now I can sure that this is because of the quadrature modulator

          Regards,
          Dhiman

        • #31610
          Profile Photo
          alistu
          Participant

          You’re welcome. And I generally believe it would be better to consider parameters like BER rather than the spectrum as a criteria to decide about system performance, since sometimes the theoretical aspect might be less obvious. Nonetheless, optical spectrum analyzer provides valuable insight into the system performance.

          Regards

    • #31616

      Hi Alistu,
      definitely i will go for designing the receiver section, and to look for BER, Q-factor and other performance parameters, Thanks for the reply..

      Regards,
      Dhiman

      • #31621
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        alistu
        Participant

        You’re welcome. I was unaware that the receiver was not implemented, though.

        Regards

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