When we’re dealing with Optical Network Elements (ONEs) that include optical amplifiers, it’s important to note a key change in signal quality. Specifically, the Optical Signal-to-Noise Ratio (OSNR) at the points where the signal exits the system or at drop ports, is typically not as high as the OSNR where the signal enters or is added to the system. This decrease in signal quality is a critical factor to consider, and there’s a specific equation that allows us to quantify this reduction in OSNR. By using following equations, network engineers can effectively calculate and predict the change in OSNR, ensuring that the network’s performance meets the necessary standards.
Where:
osnrout : linear OSNR at the output port of the ONE
osnrin : linear OSNR at the input port of the ONE
osnrone : linear OSNR that would appear at the output port of the ONE for a noise free input signal
If the OSNR is defined in logarithmic terms (dB) and the equation(Eq.1) for the OSNR due to the ONE being considered is substituted this equation becomes:
Where:
OSNRout : log OSNR (dB) at the output port of the ONE
OSNRin : log OSNR (dB) at the input port of the ONE
Pin : channel power (dBm) at the input port of the ONE
NF : noise figure (dB) of the relevant path through the ONE
h : Planck’s constant (in mJ•s to be consistent with in Pin (dBm))
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