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Multimode 850 nm vertical cavity surface-emitting lasers (VCSELs) suitable for high bit rate operation are studied. VCSELs with oxide aperture diameters of 5-7 μm show a high −3 dB modulation bandwidth (∼20 GHz) and D-factor (∼ 8 GHz mA −1/2 ). To allow low capacitance a multiple layer oxide-confined aperture design was applied. Eye diagrams are clearly open up to 35 Gbit s −1 at the temperature of 25 • C. Using 35 μm diameter PIN photodiodes and 6 μm oxide aperture diameter VCSELs error-free 25 Gbit s −1 (defined as a bit error ration of 1 × 10 −12 ) optical fiber communication links were tested over 100 m of standard OM3 multimode optical fibers at 25 • C and 85 • C. The received optical power for error-free operation was below −4 dBm at both temperatures. A VCSEL reliability study at 95 • C was performed at the high current densities (∼18 kA cm −2 ) needed for error-free 25 Gbit s −1 operation at elevated temperatures. After 6000 h a slight increase (less than 5%) of the output optical power at a constant current was observed and most likely due to an ohmic contact burn in effect within the first 2000 h of the study. The results clearly indicate that 25 Gbit s −1 850 nm oxide-confined VCSELs with a complex AlGaO multilayer aperture design and with step-graded Al-compositions have the potential for reliable operation.

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