Optimum Damping Level for High-Speed Large Signal VCSEL modulation

The commercial optical interconnects used in datacenters and high performance computers have recently been pushed to data rates of 25-28 Gbps. Near future standards will require even higher data rates and further work to increase the speed is therefore necessary. Typically the 850 nm vertical-cavity surface-emitting laser (VCSEL) is employed as light source in such optical interconnects, due to its low-cost fabrication and excellent high-speed properties at low drive currents.Previously, we have shown that a reduction of the damping of the VCSEL small signal modulation response can increase the modulation bandwidth (BW) and that there exists an optimum damping for maximum BW. This allowed us to demonstrate a record-high small signal modulation BW of 28 GHz and error-free [bit error rate (BER