Abstract
We propose a cost-effective digital coherent scheme with low-complexity digital signal processing (DSP) for short-reach optical interconnection. Differential 8-ary quadrature amplitude modulation (D8QAM) with 1-decision-aided adaptive differential decoding bypasses carrier recovery and enables cycle-slip-free operation. We experimentally demonstrate that the receiver sensitivity of 400-Gb/s D8QAM is insensitive to the laser type, and is the same as 400-Gb/s 16QAM in the case of 2-km transmission with a distributed feedback (DFB) laser. The proposed adaptive equalizer (AEQ) using real-valued finite impulse response (FIR) filters and shorter tap lengths for the real-imaginary filters allows hardware-efficient implementation with high robustness to the receiver-side timing skew. In the case of 400-Gb/s D8QAM 10-km transmission, our AEQ achieves comparable performance as conventional 4×4 real-valued multi-input multi-output (MIMO) and the existing simplified AEQs with complexity reduction of 50% and 14% respectively.
Highlights
New applications such as 5G, cloud computing, augmented/virtual reality and storage have significantly driven traffic demands
We experimentally demonstrate that the proposed adaptive equalizer (AEQ) achieves comparable performance as conventional 4×4 real-valued multi-input multi-output (MIMO) with 40% and 50% lower complexity, for 68-GBaud Differential 8-ary quadrature amplitude modulation (D8QAM) 2-km and 10-km transmission respectively
We firstly investigate the extreme performance of 400-Gb/s 16QAM and D8QAM using 100-kHz linewidth external cavity laser (ECL) and 23-tap conventional 4×4 MIMO
Summary
New applications such as 5G, cloud computing, augmented/virtual reality and storage have significantly driven traffic demands. To realize beyond 400-Gb/s short-reach transmission, traditional intensity-modulation direct detection solution requires more parallel paths, larger electrical bandwidth, or advanced DSP, which inevitably increases the cost or power consumption. The deployment is still challenging due to the use of narrow-linewidth lasers in both ends and high DSP-associated power consumption. To solve these problems, self-homodyne detection using a transmitted pilot tone as the local oscillator (LO) has been proposed [3,4,5]. The pilot tone transmitted by additional fiber [3] or polarization [4] sacrifices fiber capacity and requires high output power lasers to extend system reach
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