We experimentally demonstrated the application in ultrahigh spectral density long-haul optical systems of tight prefiltering to generate “quasi-Nyquist wavelength division multiplexing” signals together with the use of pure-silica core fiber and hybrid Raman/erbium-doped fiber amplification. The transmission of polarization-multiplexed quadrature-amplitude modulation with 8 symbols (PM-8QAM) at 138 Gb/s and channel spacing equal to 1.22\,×\,(symbol rate) was demonstrated, reaching over 4000 km at net spectral efficiency (SE) of 4.1 b/s/Hz. In our experiment, we achieved to date highest per-carrier symbol rate (23 Gbaud), SE (4.1 b/s/Hz), and (SE)\,×\,(distance) product (16655 b/s/Hz·km) for non-orthogonal frequency-division multiplexing transmission using PM-8QAM modulation.
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Cigliutti et al. (2011) studied this question.
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