Chapter: Optical Communication and Networking : Fiber Optic Receiver and Measurements
Quantum Limit
QUANTUM LIMIT
·
An ideal photodetector which has unity
quantum efficiency and which produces no dark current, that is no electron
holde pairs are generated in the absence of an optical pulse.
QUANTUM LIMIT
·
This condition, it is possible to find
the minimum received optical power required for a specific nit error rate
performance in a digital syatem. This minimum received power level is known as
the quantum limit.
·
Assume an optical pulse of energy E
falls on the photodeetector in a time interval t. This can only
be interpreted by the receiver as a 0 pulse if no electron hole pairs are
generated with the pulse with the pulse present.
·
The probability that n=0 electrons are
emitted in a time interval t is
·
Thus for a given probability Pr(o),
we can find the minimum energy E required at a specific wavelength l.
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