Zhensheng Jia

Transmission of 8 × 480-Gb/s super-Nyquist-filtering 9-QAM-like signal at 100 GHz-grid over 5000-km SMF-28 and twenty-five 100 GHz-grid ROADMs

We experimentally demonstrate a highly filtering-tolerant multi-modulus equalization (MMEQ) process for very aggressively spectrum-shaped 9-ary quadrature-amplitude-modulation (9-QAM)-like polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signal to achieve 400-Gb/s wavelength-division-multiplexing (WDM) channels on the 100-GHz grid for ultra-long-haul reach and high tolerance of the filter narrowing effect caused by reconfigurable optical add-drop multiplexers (ROADMs). We successfully transmitted 8 channels 480-Gb/s super-Nyquist (channel occupancy much less than signal baud rate) WDM signals at 100-GHz grid over 25 × 200 km conventional single-mode fiber-28 (SMF-28) with post Raman amplification and 25 ROADMs at a net spectral efficiency (SE) of 4b/s/Hz, after excluding the 20% soft-decision forward-error-correction (FEC) overhead. The system performance is significantly enhanced by the MMEQ based on 9-QAM-like constellations compared to the conventional 4 point QPSK constellation. A record transmission distance over conventional SMF-28 with a large number of ROADMs is firstly reported on the 400-Gb/s channels at 100-GHz grid.

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We have transmitted a 7×224 Gb/s/ch Nyquist wavelength-division-multiplexed signal over a 1600-km conventional single-mode fiber (SMF-28) with 80 km per span and an erbium-doped fiber amplifier-only amplification. Each channel on the 50-GHz grid is modulated using polarization-division-multiplexed quadrature-phase-shift-keying at 56 Gbaud giving a record spectral efficiency of 4 b/s/Hz. Both the post filter and the Viterbi maximum likelihood sequence detection are introduced into digital signal processing, to suppress the undesired noise, linear crosstalk enhancement, and filtering effects. The bit error ratio of all channels after transmission over a 1600-km SMF-28 is smaller than the forward error correction limit of 3.8×10-3.

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The highly filtering-tolerant performance of the 9-QAM liked super-Nyquist signal is experimentally demonstrated. Using this scheme, we successfully transmit 10 channels 440-Gb/s signal over 3000-km fiber and 10 cascaded ROADMs with 100-GHz grid based on single-carrier ETDM 110-GBaud QPSK.