Theoretical study on high-speed modulation of Fabry-Pérot and distributed-feedback quantum-dot lasers: K-factor-limited bandwidth and 10Gbit∕s eye diagrams

This paper presents a theoretical study of the high-speed modulation response of Fabry-Pérot (FP) and distributed-feedback (DFB) quantum-dot lasers based on the rate equation models, making reference to available experimental data. We show that the K-factor-limited maximum modulation bandwidth increases with the maximum optical gain and that there is an optimum cavity loss to maximize the bandwidth at a given maximum gain, enabling us to design the bandwidth of FP lasers as well as DFB lasers with and without a phase shift. We present modulation wave forms of FP quantum-dot lasers to indicate that the maximum modal gain of 30–40cm−1 is sufficient for 10Gbit∕s eye opening, which explains the recent success of 10Gbit∕s modulation of the quantum-dot laser with ten dot layers in the active region having the maximum modal gain of 35cm−1. We show a design for low-driving-current 10Gbit∕s operation by shortening the cavity length with the optimum cavity loss maintained by the high-reflectivity coating.