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With the increasing bandwidth demand of optical interconnects, directly modulated VCSELs with ultimate speed ratings are needed [1]. For serial 100 Gbps solutions, today´s VCSELs have to increase their high-speed performance. Here we report about our next generation devices. The devices discussed here are an optimized version of our very successful high-speed, temperature-stable 980 nm VCSELs [2], and serve as reference-structure for high-contrast-grating high-speed VCSELs, which are in fabrication. Sharing the very short half-lambda cavity and a binary bottom-mirror with 32 pairs, levels are further optimized in order to minimize internal loss. Like previously, parasitics are controlled by two oxide apertures and highly conducting current-spreading layers. InGaAs MQW active layers with strain compensated GaAsP barriers were utilized for high differential gain. The 22 -pair Al12Ga88As/Al90Ga10As top-mirror was replaced by an 18-pair GaAs/Al90Ga10As mirror for lower photon lifetime, better confinement and better heat extraction. The epistructure was grown by IQE Europe. A similar structure with a high-contrast-grating (HCG) mirror is in process. A detailed small-signal analysis is performed. The VCSELs showed modulation bandwidth around and exceeding 30 GHz. The measured data was fitted to single-mode and multi-mode rate-equation based models assuming selforganized carrier reservoirs formed by spatial hole burning. The common set of figures of merit is extended consistently to explain dynamic properties caused by carrier fluctuations. Mode control, which can ideally be performed by high-contrast-gratings, seems essential for next generation highspeed VCSEL devices.
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