
distance (linear system), the same BER can be achieved with 3 dB worse OSNR.
Therefore, twice the number of optical amplifiers can be tolerated, and hence twice
the number of spans can be bridged. As a result, in a system where transmission
suffers less from fiber nonlinearity, the reach can be extended considerably. Many
techniques can be used to reduce the impact of fiber nonlinearity, including advanced
modulation formats, new fiber designs and advanced dispersion mapping.
A comparison of two systems having identical back-to-back required OSNRs but
different tolerances to fiber nonlinearity is represented in Figure 2.24. System B has a
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