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 present results from our new generation of high performance 850 nm oxide confined vertical cavity surface-emitting lasers (VCSELs). With devices optimized for high-speed operation under direct modulation, we achieve record high 3dB modulation bandwidths of 28 GHz for ~4 µm oxide aperture diameter VCSELs, and 27 GHz for devices with a ~7 µm oxide aperture diameter. Combined with a high-speed photoreceiver, the ~7 µm VCSEL enables error-free transmission at data rates up to 47 Gbit/s at room temperature, and up to 40 Gbit/s at 85°C.

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The impedance characteristics and the effects of photon lifetime reduction on the performance of high-speed 850 nm VCSELs are investigated. Through S 11 measurements and equivalent circuit modeling we show that the parasitic mesa capacitance can be significantly reduced by using multiple oxide layers. By performing a shallow surface etch (25 -55 nm) on the fabricated VCSELs, we are able to reduce the photon lifetime by up to 80% and thereby significantly improve both static and dynamic properties of the VCSELs. By optimizing the photon lifetime we are able to enhance the 3dB modulation bandwidth of 7 µm oxide aperture VCSELs from 15 GHz to 23 GHz and finally demonstrate errorfree transmission at up to 40 Gbit/s.

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