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We propose a joint look-up-table (LUT)-based nonlinear predistortion and digital resolution enhancement scheme to achieve high-speed and low-cost optical interconnects using low-resolution digital-to-analog converters (DACs). The LUT-based predistortion is employed to mitigate the pattern-dependent effect (PDE) of a semiconductor optical amplifier (SOA), while the digital resolution enhancer (DRE) is utilized to shape the quantization noise, lowering the requirement for the resolution of DAC. We experimentally demonstrate O-band intensity modulation and direct detection (IM/DD) transmission of 124-GBd 4/6-level pulse-amplitude modulation (PAM)-4/6 and 112-GBd PAM-8 signals over a 2-km standard single-mode fiber (SSMF) with 3/3.5/4-bit DACs. In the case of 40-km SSMF transmission with an SOA-based preamplifier, 124-GBd on-off-keying (OOK)/PAM-3/PAM-4 signals are successfully transmitted with 1.5/2/3-bit DACs. To the best of our knowledge, we have achieved the highest net data rates of 235.3-Gb/s PAM-4, 289.7-Gb/s PAM-6, and 294.7 Gb/s PAM-8 signals over 2-km SSMF, as well as 117.6-Gb/s OOK, 173.8-Gb/s PAM-3, and −231.8 Gb/s PAM-4 signals over 40-km SSMF, employing low-resolution DACs. The experimental results reveal that the joint LUT-based predistortion and DRE effectively mitigate the PDE and improve the signal-to-quantization noise ratio by shaping the noise. The proposed scheme can provide a powerful solution for low-cost IM/DD optical interconnects beyond 200 Gb/s.
Wu et al. (Wed,) studied this question.