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Quantum noise

Question asked by anrevilla on Feb 12, 2011
Latest reply on Feb 20, 2011 by anrevilla
I have been taught that the minimum amount of noise you can find in a phase insensitive optical system is the quantum noise (hvB), which correspond to -58 dBm in 0,1 nm for the third window (1550 nm).

However, an OSA frequently shows noise levels below -58 dBm in 0,1 nm. For example, in the monitoring point of an  optical amplifier (EDFA).

What is the explanation of this? Are these measurements wrongly made?  

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