Cost-effective digital coherent short-reach transmission system with D8QAM and low-complexity DSP

We propose a cost-effective digital coherent scheme with low-complexity signal processing (DSP) for short-reach optical interconnection. Differential 8-ary quadrature amplitude modulation (D8QAM) 1-decision-aided adaptive differential decoding bypasses carrier recovery and enables cycle-slip-free operation. experimentally demonstrate that the receiver sensitivity of 400-Gb/s D8QAM is insensitive to laser type, same as 16QAM in case 2-km transmission distributed feedback (DFB) laser. The proposed equalizer (AEQ) using real-valued finite impulse response (FIR) filters shorter tap lengths real-imaginary allows hardware-efficient implementation high robustness receiver-side timing skew. In 10-km transmission, our AEQ achieves comparable performance conventional 4×4 multi-input multi-output (MIMO) existing simplified AEQs complexity reduction 50% 14% respectively.