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Successful joint experiments with Deutsche Telecom (DT) on long-haul transmission of 100 G and beyond are demonstrated over standard single-mode fiber (SSMF) and inline erbium-doped fiber amplifier-only amplification. The transmission link consists of eight nodes and 950-km installed SSMF in DT's optical infrastructure with the addition of lab SSMF for extended optical reach. The first field transmission of 8 × 216.8-Gb/s Nyquist-WDM signals is reported over 1750-km distance with 21.6-dB average loss per span. Each channel modulated by a 54.2-Gbaud PDM-CSRZ-QPSK signal is on 50-GHz grid, achieving a net spectral efficiency (SE) of 4 bit/s/Hz. We also demonstrate mixed data-rate transmission coexisting with 1 T, 400 G, and 100 G channels. The 400 G uses four independent subcarriers modulated by 28-Gbaud PDM-QPSK signals, yielding the net SE of 4 bit/s/Hz while 13 optically generated subcarriers from single optical source are employed in 1 T channel with 25-Gbaud PDM-QPSK modulation. The 100 G signal uses real-time coherent PDM-QPSK transponder with 15% overhead of soft-decision forward-error correction. The digital postfilter and 1-bit maximum likelihood sequence estimation are introduced at the receiver DSP to suppress noise, linear crosstalk, and filtering effects. Our results show the future 400 G and 1 T channels utilizing the Nyquist wavelength division multiplexing technique can transmit long-haul distance with higher SE using the same QPSK format.