Changing the modulation and increasing the bandwidth does introduce some engineering challenges. When the modulation is changed from NRZ to PAM4, the available signal magnitude (also known as eye height, for the opening that looks like an eye, observable in the NRZ and PAM4 diagrams in Figure 1) is decreased by 33%. Lowering the signal magnitude means the signal-to-noise ratio is immediately affected, making PAM4 signals more
Figure 1: OSFP data rate vs. 99.9% frequency content. Modulation is shown near relevant data rates.
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