It is well know fact that photodiode beats optical bands to generate RF signal with frequency equal to difference of frequencies of the optical bands. When I am detecting optical with optical spectrum given below used photo diode, I am not able to cmprehend some results in Rf spectrum.
The bands shown in optical spectrum are harmonics of 5Ghz signal.
20Ghz Rf signal is obtained from beating (+2,-2)
40 Ghz from beating (-2,-6) and (+2,+6)
Why is 5Ghz signal that would have been result of beating (-2,-1) and (+2,+1) absent.
Similarly Why is 15Ghz signal that would have been result of beating (-2,+1) and (-1,+2) absent.
Further why power of 40Ghz signal greater than that of 10Ghz signal in Rf spectrum
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