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A digital optical fiber communication system operating at a wavelength of 1 μm requires a maximum bit error rate of 10-9. What is the theoretical quantum limit at the receiver in terms of the quantum efficiency of the detector and the energy of an incident photon?

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Quantum LImit :
The amount of energy ( Emin ) required to maintain giver bit error rate .
Zm : Average number of photons detected in one time period 
Zm= 
Bit Error   :   P(e) = 
10-9 = 
Zm = 20.7 = 
P0 =  = Emin / 
Emin = P0  = 
Hence correct option is "A" 
 
 
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