Abstract
We numerically demonstrate 80-km standard single-mode fiber transmission without optical amplification, dispersion compensation or carrier recovery using 200-Gb/s tandem single sideband modulated doubly differential QPSK. Simulation results show that doubly differential encoding enables practically constant system performance for frequency offsets within ± 2.3 GHz and allows a linewidth tolerance of 2.5 × 10-3 at 1-dB receiver sensitivity penalty. Employing 2.9-MHz linewidth lasers, the receiver sensitivity penalty at 7% HD-FEC threshold for 80-km transmission is less than 0.2 dB. By adding a 12-symbol decision feedback in the 2nd differential operation of doubly differential decoding, the receiver sensitivity is improved by 3.7 dB.
Highlights
Direct detection systems using direct modulation and advanced modulation formats [1,2] have been widely investigated for 100-Gb/s data center interconnection (DCI), where cost and power consumption are critical
Employing the simulation setup described in the last section, we investigated the performance of a 200-Gb/s tandem single sideband (TSSB) DDQPSK back-to-back system at zero frequency offset (FO), using ideal hybrids or commercially available 90 degree hybrids [19] with the specified maximum amplitude difference of 1 dB and phase imperfection of 5° between two output ports, both separately and simultaneously
The performance is degraded by 2.2 dB for a 1dB AD under all phase conditions, indicating that the system performance is more sensitive to the amplitude imbalance than to the phase imperfection. For hybrids with both 1-dB AD and 5° phase imperfection, the receiver sensitivity is 2.7 dB away from that using ideal hybrids. These results show that the amplitude balance of the 90 degree hybrid is critical to the system performance. 4.2 Frequency offset and linewidth tolerance We studied the performance of the 200-Gb/s DDQPSK back-to-back system using 100-kHz lasers for different FOs
Summary
Direct detection systems using direct modulation and advanced modulation formats [1,2] have been widely investigated for 100-Gb/s data center interconnection (DCI), where cost and power consumption are critical. Alternative solutions, which minimize DSP whilst offering high receiver sensitivity and enabling optical amplifier-free operation, would be attractive. The system is designed to operate without optical amplification, dispersion compensation or carrier recovery, and we recently reported [11] that this can be enabled by resorting to three key technologies. We introduce a fourth technology, multi-symbol decision feedback, to effectively improve the receiver sensitivity in DDQPSK system and evaluate the potential power consumption savings enabled by DD encoding. Employing 2.9-MHz linewidth lasers with FOs up to ± 2.3 GHz results in a receiver sensitivity below −25.4 dBm at 7% FEC threshold after 80-km transmission with less than 0.2-dB transmission penalty. By including 13-tap multi-symbol decision feedback [14] with unity tap weights in the 2nd differential stage, the receiver sensitivity is improved by 3.7 dB
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