DDO-OFDM WDM

[Duy Le Nguyen]

Hi everyone.

Sorry to bother you. But can i ask you some questions.
I’am newbie and by following the OFDM modulation sample in sample folder, I’m trying design a DDO-OFDM WDM.
In that file. We have Quadrature Modulator frequency is 7.5 GHz and the CW laser frequency is 193.1 THz, so the reference wavelength of optical fiber is 193.1075 THz.
But if it’s a WDM system with CW laser is 193.1,193.2…, so
1. What value we can set to reference wavelength of optical fiber ?
2. How can we calculate the Bandwidth of MUX and gain of the first Optical amplifier ( the one before Loop, usally is 13dB gain and 4dB figure noise).
3. The constellation isn’t correct, what can i do to enhance my system?

I’m very appreciated for your help. I attached simulation file below.
Thanks and regards.

[Dr. Dhiman Kakati]

Hi Duy Le Nguyen,
Unable to open your attached design file. Showing some error, “failed to load from storage”.

Regards,
Dhiman

[Duy Le Nguyen]

Hi Dhiman Kakati.

Thanks for your reply.
I tried to rebuild my DDO-OFDM WDM system. And now I have the constellation like this:

It doesn’t seems true. What can i do to enhance it?
I re-attached new simulation file below.

Best regards.
Duy.

[Dr. Dhiman Kakati]

Hi Duy le Nguyen, This timen also I am unable to open the design attached in the above reply. From the constellation I can say that your system is almost done. need to adjust little. I am using OptiSystem V13 and could better help in this if I could open the file attached. I think you need to adjust the parameters in the MZM. and a little bit rotation of constellation points are noticed. Recheck of all the phase components.

Regards,
Dhiman

[Duy Le Nguyen]

Hi Dhiman Kakali.

I’m using Optisystem V14. It maybe the reason you couldn’t open my file.
I’m very appreciated for your help. I tried to adjust the parameters in MZM.
My parameters in MZM:
Extinction ratio : 60dB; Insert loss :1dB.
And Bias voltage 1 and 2 are 0, 2
But it’s still circle constellation.

Regards

[Dr. Dhiman Kakati]

Hi Duy le Nguyen,
Did you try to check the output by decreasing the bit rate of the system.

Regards,
Dhiman

[Duy Le Nguyen]

Hi everybody.

I’m done with my 4-QAM DDO-OFDM WDM system now. But I want to develop it to 16-QAM.
What parameters should I change?.
I known the bit per symbol of QAM generator and reference bit rate of OFDM demodulator OS12 must be changed.

How about the cut off frequence of filters and bandwidth of MUX (DEMUX)? What equation i can use?

If you have time please answer me.

Thanks and regards

[Dr. Dhiman Kakati]

and in the quadrature modulator try to set frequency same as symbol rate, in most of the cases I found better results by doing so.

Regards,
Dhiman

[Duy Le Nguyen]

Hi Dhiman.

Thanks for your enthusiasm . Do you mean symbol rate is global parameter symbol rate or OFDM symbol rate or M-QAM symbol rate?
and How about the cut off frequency of filter and bandwidth of MUX (DeMUX). Did you try to change those parameters?

Regards
Duy.

[Dr. Dhiman Kakati]

Hi Duy Le,
the bandwith of the mUX and Demux strongly depend on the modulation scheme and other parameters, use one Optical spectrum visualizer and then try to find the approx bandwidth required from there. I am not aware of mathematics. Hope from Other members.

[Duy Le Nguyen]

Hi Dihiman.

I’m very appreciated for you help. And how about the symbol rate you mentioned in previous comment.

and in the quadrature modulator try to set frequency same as symbol rate, in most of the cases I found better results by doing so.

Regards,
Dhiman

Is it OFDM symbols?

Regards.

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