Performance Study of 100-Gb/s Super-Nyquist QPSK and Nyquist 8QAM over 25-GHz Spacing

To enable a 100 Gb/s over 25-GHz long-haul transmission solution, Nyquist 8-ary quadrature-amplitude modulation (QAM) and super-Nyquist quadrature phase-shifted keying (QPSK) are promising candidates. Nyquist 8QAM is experimentally demonstrated to have slightly better nonlinear tolerance than super-Nyquist QPSK at the same bit rate. The super-Nyquist QPSK signal suffers higher performance fluctuation depending on bandwidth squeezing.