Impact of Photon Lifetime on High-Speed VCSEL Performance

We investigate the impact of reduced photon lifetime on the static and dynamic performance of high-speed, oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The photon lifetime is reduced by a shallow-surface etch that lowers the reflectivity of the top mirror. From an analysis of the dependence of slope efficiency on mirror loss (etch depth) and temperature, we deduce values for the internal quantum efficiency and the internal optical loss and their dependencies on temperature. From an analysis of the dependence of the small-signal-modulation response on photon lifetime (etch depth) and temperature, we deduce values for differential gain and gain compression, and their dependencies on photon lifetime and temperature. We find a tradeoff between high resonance frequency and low damping for speed enhancement, leading to an optimum photon lifetime close to 3 ps for this particular VCSEL design that enables a modulation bandwidth of 23 GHz and error-free transmission at 40 Gb/s.