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.