Beyond 1.6 Tb/s Net Rate PAM Signal Transmission for Rack-Rack Optical Interconnects With Mode and Wavelength Division Multiplexing

In this article, a beyond 1.6 Tb/s net rate pulse amplitude modulation (PAM) communication system is experimentally demonstrated for 20 m rack-rack optical interconnects with low cost intensity modulation direct detection (IM-DD) architecture, which is enabled by mode division multiplexing (MDM) and wavelength division multiplexing (WDM). The MDM with three linearly polarized modes is realized by a multiplane light conversion (MPLC) mode multiplexer with the maximum modal crosstalk less than - 20 dB. The experimental results show that 2.01 Tb/s (1.84 Tb/s net rate) PAM-6 signal carried on three modes and four wavelengths is successfully transmitted over 20 m standard OM2 multimode fiber (MMF) with the BERs of received signals from all channels below hard decision forward error correction (HD-FEC) threshold of 3.8 × 10-3. Look-up table (LUT) pre-distortion and Volterra nonlinear equalizer (VNLE) are employed for nonlinear impairment mitigation to improve the system performance. Compared to linear feedforward equalizer (FFE), 0.3 dB and 1 dB receiver sensitivity improvements are obtained by LUT and VNLE, respectively. To the best of our knowledge, our proposed scheme achieves the highest bit rate of 167.5 Gb/s per wavelength in MDM system with IM-DD structure. The experimental results show that our proposed PAM MDM communication scheme is a promising candidate for future 1.6 Tb/s short reach rack-rack optical interconnects.