Abstract

In this article, we experimentally demonstrate the amplifier-less transmission of beyond 100-Gbit/s signal with advanced modulation formats including discrete multi-tone (DMT) and pulse amplitude modulation (PAM) in an intensity modulation direct detection (IM-DD) system for 40-km datacenter interconnects edge (DCI-Edge) utilizing a low cost commercial 10G-class O-band directly modulated laser (DML). During the transmission of DMT signal, Chow Cioffi Bingham algorithm-based bit-loading (CCB-BL) and discrete-Fourier-transform spread (DFT-spread) techniques are both discussed in the bandwidth-limited communication system. For the PAM single carrier communication system, look-up table (LUT) pre-distortion and time-domain pre-equalization schemes are jointly employed at the transmitter side to mitigate nonlinear distortions and insufficient bandwidth induced impairments, respectively. The results show that 105-Gbit/s DFT-spread DMT, 115-Gbit/s CCB-BL DMT, and 120-Gbit/s PAM-8 signals are successfully transmitted over 40-km single mode fiber (SMF) with the bit-error-rate (BER) below hard decision forward error correction (HD-FEC) threshold of 3.8 × 10^–3. 120-Gbit/s DFT-spread DMT and CCB-BL DMT signals allocated within 20-GHz bandwidth can be successfully transmitted over 20-km SMF, and the receiver sensitivity of DFT-spread DMT outperforms CCB-BL DMT by 1.5-dB at the BER of 3.8 × 10^–3. Due to the flexibility of bit-loading technique, when the allocated bandwidth of 120-Gbit/s CCB-BL DMT signal extends from 20-GHz to 25-GHz, the required received optical power (ROP) of CCB-BL DMT can be lower than DFT-spread DMT by 1-dB at the BER of 3.8 × 10^–3 over 20-km SMF transmission. In 120-Gbit/s PAM-8 system, LUT pre-distortion technique improves the system receiver sensitivity by more than 1-dB over 40-km SMF transmission. This is the first time to discuss and implement different advanced modulation formats to achieve 100-Gbit/s/λ transmission in a 40-km amplifier-less IM-DD system with a low-cost O-band 10G class DML. Both CCB-BL DMT and LUT pre-distortion assisted PAM-8 can achieve a BER lower than HD-FEC threshold of 3.8 × 10^–3 when the net rate per optical carrier is higher than 100-Gbit/s, which are promising solutions for 40-km four-lane 400-GbE DCI-Edge applications.

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