Beating of optical signals by photodiode

[aasif bashir dar]

Kindly see question from one of my reviewer.
For reference; RFmodulation frequency is used to generate by external modulation optical bands is 5GHz.The optical signal shown in optical spectrum is amplified with optical amplifier of 30 dB gain before detection by diode.
1 and 2 are 1st order optical side bands
6 and 4 are 2nd order optical side bands
And 5 and 3 are 6th order bands.
….
20Ghz Rf signal is generated from beating (6,4)
40 Ghz from beating (5,6) and (4,3)
Why is 5Ghz signal that would have been result of beating (6,1) and (2,4) absent.
Similarly Why is 15Ghz signal that would have been result of beating (6,2) and (1,4) absent.
Further why power of 40Ghz signal greater than that of 10Ghz signal in Rf spectrum.

Attachments:

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   20200524_205019.jpg
   

[Ahmad Atieh]

Dear Aasif,
All beating frequencies are there. However, there level depends on the original tone amplitude. I’ve marked some of these beating.
You may try to improve the resolution by increase the sample per bit and increase signals amplitude to show better the beatings.

Regards,
Ahmad

Attachments:

1. 

   Inked20200524_205019-002_LI.jpg
   

[aasif bashir dar]

Respected sir,
Thans for you kind reply.
I guess what you indicated by arrows in the uploaded image are noise spikes. To prove my point, I have provide here signal only rf spectrum, noise only rf spectrum and combined spectrum.

The rf frequency bands in rf spectrum can not be justified by the optical spectrum of signal that is beated.
Kindly make me under beating of what frequency bands resulted in 10Ghz signal.
Why 5 Ghz frequency signal is absent. Why 15 Ghz frequency is absent in Rf spectrum.

With regards

Attachments:

1. 

   Optical-spectrum-to-be-beated-by-photodiode.pdf
   

[aasif bashir dar]

Respected sir,
Thans for you kind reply.
I guess what you indicated by arrows in the uploaded image are noise spikes. To prove my point, I have provided here signal only rf spectrum, noise only rf spectrum and combined spectrum.

The rf frequency bands in rf spectrum can not be justified by the optical spectrum of signal that is beated.
Kindly make me understand beating of what frequency bands resulted in 10Ghz signal.
Why 5 Ghz frequency signal is absent. Why 15 Ghz frequency is absent in Rf spectrum.

With regards

Attachments:

1. 

   Optical-spectrum-to-be-beated-by-photodiode-1.pdf
   

[Ahmad Atieh]

Hello,
Please send me your project as a zip file to ahmad.atieh@optiwave.com to check it out and provide feedback. Meanwhile, attached is a list of all possible beatings.
Regards,
Ahmad

Attachments:

1. 

   list-of-harmonics.pdf
   

[Author]

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