How to restrict side bands in Direct Modulation of RF (Analogue) signal

[Ibn Aziz]

Hi every one !
Hope u all are fine.

I am working on Direct Modulation of RF signal with CW laser. The frequency of RF signal is 12.5 GHz and Bit rate is 128 Mega bits/sec.

When i directly modulate RF signal with CW Laser (a component in Optical transmitter library) ” then i got number of side bands as shown in below figure.1 (i have used “sample per bit = 64” here in this case).

Now problem is that i need only three side bands on right side of center frequency and three bands on left side of center
frequency but i don’t know how to reduce side-bands to only three on both sides of center frequency.

I have also tried the above case with sample per bit = 32 and the number of side bands i got is shown in fig.2.
I have also done the same scenario by varying the amplitude of RF signal but that does not effect much on side bands.
I have also attached the components i have used in my case as shown in figure.3.

Kindly guide me if anyone know the solution or how to resolve the above problem. I will be very thankful to you for your this act of kindness.

Best Regards

Attachments:

1. 

   figure.1-with-sample-per-bit64.jpg
   

2. 

   Figure.2.-with-sample-per-bit-32.jpg
   

3. 

   figure.3.-scenario.jpg
   

[Ibn Aziz]

if any one know any other technique which involves Direct Modulation of RF signal with CW laser and results into 3 side bands on both side of center frequency, plz share.

Best Regards.

[Abdallah Ismail]

Why didn’t you try to use a band-pass filter to get the band you like in your comb generator?

[Ibn Aziz]

Thanks Abdallah for ur kind response.
Yes, Abdallah i can get by using band pas filter but i am not using it because i want to make cost efficient system which includes as less components as possible. Therefore i am trying to acquire desire side bands by using optical processing techniques (on the components as shown in fig.3 attached above) rather then using any optical components preferably.

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