Error free transmission over multimode fibre at data rates up to 32 Gbit/s at 258C and 25 Gbit/s at 858C using an oxide confined 850 nm VCSEL biased at a current density of 11 -14 kA/cm 2 is demonstrated. The VCSEL is optimised for high-speed by reducing capacitance and self-heating and by using strained InGaAs quantum wells for high differential gain.Introduction: Vertical cavity surface emitting lasers (VCSELs) operating at speeds 25 Gbit/s under direct current modulation will be needed in future high capacity, short reach data communication links (e.g. 32 Gbit/s Fibre Channel and 100 Gigabit Ethernet). The wavelength should preferably be 850 nm, which is the current standard for data communication links, where high speed multimode fibre is available (OM3 and higher speed versions). The VCSEL should also be biased at a current density low enough for reliable operation, while at the same time having a bandwidth sufficient for modulation at high-speed.To date, modulation at speeds as high as 35 and 40 Gbit/s have been demonstrated with VCSELs emitting at 980 and 1100 nm, respectively [1,2]. VCSELs at these wavelengths reach modulation bandwidths above 20 GHz by employing strained InGaAs quantum wells (QWs) for high differential gain and binary alloys in the distributed Bragg reflectors (DBRs) for improved heat conduction. At 850 nm, a modulation speed of 30 Gbit/s was recently demonstrated using an oxide confined VCSEL design with reduced capacitance and reduced aperture diameter [3]. However, in all these cases the VCSEL is biased at a relatively high current density of 20 -60 kA/cm 2 , which may limit the device lifetime.Here we report on successful transmission experiments, demonstrating error free transmission, over OM3 fibre at data rates up to 32 Gbit/s at 258C and 25 Gbit/s at 858C using a high-speed, oxide confined 850 nm VCSEL [4] biased at a current density of 11 kA/cm 2 at 258C and 14 kA/cm 2 at 858C.

We show experimentally that polarization mode hopping in quantum dot vertical cavity surface emitting lasers (VCSELs) takes place between nonorthogonal elliptically polarized modes. In contrast to quantum well VCSELs the average dwell time decreases with injection current. This decrease is by 8 orders of magnitude: from seconds to nanoseconds and is achieved without any modifications of the VCSEL internal anisotropies. The observed scaling happens in a range of currents as wide as 8 times the threshold value.

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980 nm vertical-cavity surface-emitting lasers based on submonolayer growth of quantum dots show clearly open eyes and operate error free with bit error rates better than 10 −12 at 25 and 85 • C for 20 Gb/s without current adjustment. The peak differential efficiency only reduces from 0.71 to 0.61 W/A between 25 and 85 • C; the maximum output power at 25 • C is above 10 mW.