One-Sample-per-Symbol Non-Linear Equalization of Directly Modulated Lasers

Recently, we proposed a novel linearization method for directly-modulated lasers (DMLs), called the ABCD approximation method. This method achieves a substantial reduction in laser non-linearity, while maintaining low implementation complexity. In this paper, we introduce a novel one sample-per-symbol (SpS) implementation of the ABCD approximation method, further reducing its implementation complexity, hence improving real-world potential. As a proof-of-concept, the method is experimentally demonstrated using a 7 GHz 850 nm VCSEL specified for 10 Gb/s NRZ modulation. Specifically, we implement two variants of the method based on three-tap T-spaced finite impulse response [FIR(3,T)] filters for 16 Gb/s NRZ modulation. Signal quality for each variant (16 GSa/s) is compared with conventional NRZ modulation and its corresponding three-SpS implementation (48 GSa/s). The results show a significant improvement in eye height for both variants over the conventional NRZ modulation. Additionally, the Stretched A variant yields reduced eye skew and improved eye symmetry. Moreover, the one-SpS implementation results in a small reduction in eye height of 0.98 dB and 0.57 dB for the two variants, respectively, compared to the three-SpS implementation. This demonstrates the effective mitigation of VCSEL non-linearity despite the one-SpS implementation. These findings highlight the potential of deploying low-bandwidth devices, and simplified, cost-effective driving circuits in next-generation optical transmitters.